MAX17504 4.5V–60V, 3.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter with Internal Compensation

MAX17504 4.5V–60V, 3.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter with  Internal Compensation
EVALUATION KIT AVAILABLE
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
General Description
The
MAX17504
high-efficiency,
high-voltage,
synchronously rectified step-down converter with dual
integrated MOSFETs operates over a 4.5V to 60V
input. It delivers up to 3.5A and 0.9V to 90% VIN output
voltage. Built-in compensation across the output voltage
range eliminates the need for external components. The
feedback (FB) regulation accuracy over -40°C to +125°C
is ±1.1%. The device is available in a compact (5mm x
5mm) TQFN lead (Pb)-free package with an exposed pad.
Simulation models are available.
The device features a peak-current-mode control
architecture with a MODE feature that can be used to
operate the device in pulse-width modulation (PWM),
pulse-frequency modulation (PFM), or discontinuous
mode (DCM) control schemes. PWM operation provides
constant frequency operation at all loads, and is useful
in applications sensitive to switching frequency. PFM
operation disables negative inductor current and
additionally skips pulses at light loads for high efficiency.
DCM features constant frequency operation down to
lighter loads than PFM mode, by not skipping pulses,
but only disabling negative inductor current at light loads.
DCM operation offers efficiency performance that lies
between PWM and PFM modes. The low-resistance,
on-chip MOSFETs ensure high efficiency at full load and
simplify the layout.
Benefits and Features
● Eliminates External Components and Reduces Total Cost
• No Schottky-Synchronous Operation for High
Efficiency and Reduced Cost
• Internal compensation for Stable Operation at Any
Output Voltage
• All Ceramic Capacitor Solution: Ultra-Compact
Layout with as Few as Eight External Components
●
Reduce Number of DC-DC Regulators to Stock
• Wide 4.5V to 60V Input Voltage Range
• 0.9V to 90% VIN Output Voltage
• Delivers Up to 3.5A Over Temperature
• 200kHz to 2.2MHz Adjustable Frequency with
External Synchronization
• Available in a 20-Pin, 5mm x 5mm TQFN Package
●
Reduce Power Dissipation
• Peak Efficiency > 90%
• PFM and DCM Modes for High Light-Load Efficiency
• Shutdown Current = 2.8FA (typ)
● Operate Reliably
• Hiccup-Mode Current Limit and Autoretry Startup
• Built-In Output Voltage Monitoring—(Open-Drain
RESET Pin)
• Resistor Programmable EN/UVLO Threshold
• Adjustable Soft-Start and Pre-Biased Power-Up
• -40NC to +125NC Operation
A programmable soft-start feature allows users to reduce
input inrush current. The device also incorporates an
output enable/undervoltage lockout pin (EN/UVLO) that
allows the user to turn on the part at the desired inputvoltage level. An open-drain RESET pin provides a
delayed power-good signal to the sys­tem upon achieving
successful regulation of the output voltage.
Applications
●
●
●
●
●
●
Industrial Power Supplies
Distributed Supply Regulation
Base Station Power Supplies
Wall Transformer Regulation
High-Voltage Single-Board Systems
General-Purpose Point-of-Load
19-6844; Rev 1; 2/14
Ordering Information appears at end of data sheet.
For related parts and recommended products to use with this part, refer
to www.maximintegrated.com/MAX17504.related.
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Absolute Maximum Ratings
VIN to PGND..........................................................-0.3V to +65V
EN/UVLO to SGND................................................-0.3V to +65V
LX to PGND................................................-0.3V to (VIN + 0.3V)
BST to PGND.........................................................-0.3V to +70V
BST to LX..............................................................-0.3V to +6.5V
BST to VCC............................................................-0.3V to +65V
FB, CF, RESET, SS, MODE, SYNC,
RT to SGND......................................................-0.3V to +6.5V
VCC to SGND........................................................-0.3V to +6.5V
SGND to PGND.....................................................-0.3V to +0.3V
LX Total RMS Current.........................................................±5.6A
Output Short-Circuit Duration.....................................Continuous
Continuous Power Dissipation (TA = +70°C) (multilayer board)
TQFN (derate 33.3mW/°C above TA = +70°C).......2666.7mW
Operating Temperature Range.......................... -40NC to +125°C
Junction Temperature.......................................................+150°C
Storage Temperature Range............................. -65NC to +160°C
Lead Temperature (soldering, 10s).................................. +300°C
Soldering Temperature (reflow)........................................+260°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Package Thermal Characteristics (Note 1)
TQFN
Junction-to-Ambient Thermal Resistance (θJA)...........30°C/W
Junction-to-Case Thermal Resistance (θJC)..................2°C/W
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer
board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.
Electrical Characteristics
(VIN = VEN/UVLO = 24V, RRT = 40.2kI (500kHz), CVCC = 2.2µF, VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET = open,
VBST to VLX = 5V, VFB = 1V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are
referenced to SGND, unless otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
60
V
INPUT SUPPLY (VIN)
Input Voltage Range
Input Shutdown Current
VIN
IIN-SH
VEN/UVLO = 0V (shutdown mode)
2.8
VFB = 1V, MODE = RT= open
118
VFB = 1V, MODE = open
162
IQ_DCM
DCM mode, VLX = 0.1V
1.16
IQ_PWM
Normal switching mode, fSW = 500kHz,
VFB = 0.8V
9.5
IQ_PFM
Input Quiescent Current
4.5
4.5
µA
1.8
mA
ENABLE/UVLO (EN/UVLO)
EN/UVLO Threshold
EN/UVLO Input Leakage Current
VENR
VEN/UVLO rising
1.19
1.215
1.24
VENF
VEN/UVLO falling
1.068
1.09
1.111
-50
0
+50
nA
4.75
5
5.25
V
VCC = 4.3V, VIN = 6V
26.5
54
100
mA
VIN = 4.5V, IVCC = 20mA
4.2
IEN
VEN/UVLO = 0V, TA = +25ºC
V
LDO
VCC Output Voltage Range
VCC Current Limit
VCC Dropout
www.maximintegrated.com
VCC
IVCC-MAX
VCC-DO
6V < VIN < 60V, IVCC = 1mA
1mA ≤ IVCC ≤ 25mA
V
Maxim Integrated │ 2
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Electrical Characteristics (continued)
(VIN = VEN/UVLO = 24V, RRT = 40.2kI (500kHz), CVCC = 2.2µF, VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET = open,
VBST to VLX = 5V, VFB = 1V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are
referenced to SGND, unless otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
VCC_UVR
VCC rising
4.05
4.2
4.3
VCC_UVF
VCC falling
3.65
3.8
3.9
High-Side nMOS On-Resistance
RDS-ONH
ILX = 0.3A
165
325
mΩ
Low-Side nMOS On-Resistance
RDS-ONL
ILX = 0.3A
80
150
mΩ
LX Leakage Current
ILX_LKG
VLX = VIN - 1V, VLX = VPGND + 1V,
TA = +25ºC
-2
+2
µA
VSS = 0.5V
4.7
5
5.3
µA
MODE = SGND or MODE = VCC
0.89
0.9
0.91
MODE = open
0.89
0.915
0.936
0 < VFB < 1V, TA = +25ºC
-50
VCC UVLO
V
POWER MOSFET AND BST DRIVER
SOFT-START (SS)
Charging Current
ISS
FEEDBACK (FB)
FB Regulation Voltage
VFB_REG
FB Input Bias Current
IFB
+50
V
nA
MODE
MODE Threshold
VM-DCM
MODE = VCC (DCM mode)
VM-PFM
MODE = open (PFM mode)
VM-PWM
MODE = GND (PWM mode)
VCC 1.6
V
VCC/2
1.4
CURRENT LIMIT
Peak Current-Limit Threshold
Runaway Current-Limit Threshold
IPEAK-LIMIT
IRUNAWAY-LIMIT
Valley Current-Limit Threshold
ISINK-LIMIT
PFM Current-Limit Threshold
IPFM
MODE = open or MODE = VCC
4.4
5.1
4.9
-0.16
MODE = GND
5.85
A
5.7
6.7
A
0
+0.16
-1.8
MODE = open
0.6
0.75
0.9
RRT = 102kΩ
180
200
220
A
A
RT AND SYNC
Switching Frequency
fSW
SYNC Frequency Capture Range
SYNC Pulse Width
SYNC Threshold
www.maximintegrated.com
RRT = 40.2kΩ
475
500
525
RRT = 8.06kΩ
1950
2200
2450
RRT = OPEN
460
500
540
fSW set bt RRT
1.1 x
fSW
1.4 x
fSW
50
VIH
VIL
kHz
kHz
ns
2.1
0.8
V
Maxim Integrated │ 3
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Electrical Characteristics (continued)
(VIN = VEN/UVLO = 24V, RRT = 40.2kI (500kHz), CVCC = 2.2µF, VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET = open,
VBST to VLX = 5V, VFB = 1V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are
referenced to SGND, unless otherwise noted.) (Note 2)
PARAMETER
VFB Undervoltage Trip Level to
Cause Hiccup
SYMBOL
CONDITIONS
VFB-HICF
HICCUP Timeout
MIN
TYP
MAX
UNITS
0.56
0.58
0.6
V
(Note 3)
Minimum On-Time
tON-MIN
Minimum Off-Time
tOFF-MIN
32768
140
LX Dead Time
Cycles
135
ns
160
ns
5
RESET
RESET Output Level Low
IRESET = 1mA
RESET Output Leakage Current
TA = TJ = +25ºC, VRESET = 5.5V
-0.1
ns
0.4
V
+0.1
µA
VOUT Threshold for RESET
Assertion
VFB-OKF
VFB falling
90.5
92
94
%
VOUT Threshold for RESET
Deassertion
VFB-OKR
VFB rising
93.8
95
97.2
%
RESET Deassertion Delay After FB
Reaches 95% Regulation
1024
Cycles
165
ºC
10
ºC
THERMAL SHUTDOWN
Thermal Shutdown Threshold
Temperature rising
Thermal Shutdown Hysteresis
Note 2: All limits are 100% tested at +25°C. Limits over temperature are guaranteed by design.
Note 3: See the Overcurrent Protection/HICCUP Mode section for more details.
www.maximintegrated.com
Maxim Integrated │ 4
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Typical Operating Characteristics
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = 2 x 2.2µF, CVCC = 2.2µF, CBST = 0.1µF, CSS = 12,000pF, RT = MODE = open, TA = TJ
= -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise noted.)
5V OUTPUT, PWM MODE,
FIGURE 3 CIRCUIT,
EFFICIENCY vs. LOAD CURRENT toc01
100
100
90
VIN = 24V
70
VIN = 36V
VIN = 48V
VIN = 12V
60
50
80
VIN = 24V VIN = 36V
70
VIN = 12V
60
EFFICIENCY (%)
80
VIN = 48V
0
40
500 1000 1500 2000 2500 3000 3500
LOAD CURRENT (mA)
70
VIN = 48V
VIN = 24V VIN = 36V
100
1000
3500
VIN = 48V
VIN = 36V
VIN = 24V
70
60
VIN = 12V
50
VIN = 12V
40
40
MODE = OPEN
1
10
100
1000
30
3500
MODE = VCC
1
3.3V OUTPUT, DCM MODE,
FIGURE 4 CIRCUIT,
EFFICIENCY vs. LOAD CURRENT
100
OUTPUT VOLTAGE (V)
VIN = 12V
60
50
40
10
100
LOAD CURRENT (mA)
www.maximintegrated.com
1000
5.05
toc07
VIN = 36V
5.04
5.03
5.02
5.01
VIN = 12V VIN = 48V
5.00
4.99
MODE = VCC
1
3500
5.06
VIN = 24V
70
1000
5.07
VIN = 36V
80
100
5V OUTPUT, PWM MODE,
FIGURE 3 CIRCUIT,
LOAD AND LINE REGULATION
5.08
VIN = 48V
90
10
LOAD CURRENT (mA)
LOAD CURRENT (mA)
EFFICIENCY (%)
10
5V OUTPUT, DCM MODE,
FIGURE 3 CIRCUIT,
EFFICIENCY vs. LOAD CURRENT
100
80
30
MODE = OPEN
1
LOAD CURRENT (mA)
80
30
VIN = 12V
LOAD CURRENT (mA)
90
50
VIN = 48V
VIN = 24V VIN = 36V
60
30
500 1000 1500 2000 2500 3000 3500
EFFICIENCY (%)
EFFICIENCY (%)
0
90
60
70
40
MODE = SGND
3.3V OUTPUT, PFM MODE,
FIGURE 4 CIRCUIT,
EFFICIENCY vs. LOAD CURRENT toc04
100
80
50
50
MODE = SGND
5V OUTPUT, PFM MODE,
FIGURE 3 CIRCUIT,
EFFICIENCY vs. LOAD CURRENTtoc03
100
90
EFFICIENCY (%)
EFFICIENCY (%)
90
40
3.3V OUTPUT, PWM MODE,
FIGURE 4 CIRCUIT,
EFFICIENCY vs. LOAD CURRENT toc02
3500
4.98
VIN = 24V
MODE = SGND
0
500 1000 1500 2000 2500 3000 3500
LOAD CURRENT (mA)
Maxim Integrated │ 5
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Typical Operating Characteristics (continued)
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = 2 x 2.2µF, CVCC = 2.2µF, CBST = 0.1µF, CSS = 12,000pF, RT = MODE = open, TA = TJ
= -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise noted.)
5V OUTPUT, PFM MODE,
FIGURE 3 CIRCUIT,
LOAD AND LINE REGULATION toc09
3.3V OUTPUT, PWM MODE,
FIGURE 4 CIRCUIT,
LOAD AND LINE REGULATION
3.36
toc08
5.5
3.35
3.31
3.30
VIN = 36V
VIN = 12V
3.28
VIN = 24V
3.27
5.1
5.0
4.9
4.8
4.5
LOAD CURRENT (mA)
SWITCHING FREQUENCY (kHz)
VIN = 36V
4.6
500 1000 1500 2000 2500 3000 3500
VIN = 48V
MODE = OPEN
0
3.4
3.3
3.2
VIN = 24V
3.1
3.0
500 1000 1500 2000 2500 3000 3500
toc10
VIN = 12V
VIN = 48V
VIN = 36V
MODE = OPEN
0
500 1000 1500 2000 2500 3000 3500
LOAD CURRENT (mA)
SWITCHING FREQUENCY
vs. RT RESISTANCE
2400
VIN = 12V
4.7
MODE = SGND
0
OUTPUT VOLTAGE (V)
3.32
3.29
5.2
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
VIN = 48V
3.5
VIN = 24V
5.3
3.33
3.26
3.6
5.4
3.34
3.3V OUTPUT, PFM MODE,
FIGURE 4 CIRCUIT,
LOAD AND LINE REGULATION
LOAD CURRENT (mA)
SOFT-START/SHUTDOWN FROM EN/UVLO,
5V OUTPUT, 3.5A LOAD CURRENT,
FIGURE 3 CIRCUIT
toc12
toc11
2200
2000
VEN/UVLO
1800
2V/div
1600
1400
1200
1000
800
600
400
200
0
0
20
40
60
80
VOUT
2V/div
IOUT
2A/div
VRESET
5V/div
100
1ms/div
RRT (kΩ)
SOFT-START/SHUTDOWN FROM EN/UVLO,
3.3V OUTPUT, 3.5A LOAD CURRENT,
FIGURE 4 CIRCUIT
toc13
SOFT-START/SHUTDOWN FROM EN/UVLO,
5V OUTPUT, PFM MODE, 5mA LOAD CURRENT,
FIGURE 3 CIRCUIT
toc14
MODE = OPEN
VEN/UVLO
2V/div
VOUT
2V/div
IOUT
2A/div
VRESET
5V/div
VEN/UVLO
2V/div
VOUT
1V/div
VRESET
1ms/div
www.maximintegrated.com
2ms/div
5V/div
Maxim Integrated │ 6
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Typical Operating Characteristics (continued)
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = 2 x 2.2µF, CVCC = 2.2µF, CBST = 0.1µF, CSS = 12,000pF, RT = MODE = open, TA = TJ
= -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise noted.)
SOFT-START WITH 2.5V PREBIAS,
5V OUTPUT, PWM MODE,
FIGURE 3 CIRCUIT
SOFT-START/SHUTDOWN FROM EN/UVLO,
3.3V OUTPUT, PFM MODE, 5mA LOAD CURRENT,
FIGURE 4 CIRCUIT
toc15
VEN/UVLO
2V/div
SOFT-START WITH 2.5V PREBIAS,
3.3V OUTPUT, PFM MODE,
FIGURE 4 CIRCUIT
toc17
toc16
VEN/UVLO
VEN/UVLO
2V/div
2V/div
1V/div
2V/div
VOUT
VRESET
1V/div
VOUT
5V/div
VRESET
VOUT
VRESET
5V/div
5V/div
MODE = SGND
MODE = OPEN
2ms/div
MODE = OPEN
1ms/div
STEADY-STATE SWITCHING WAVEFORMS,
5V OUTPUT, 3.5A LOAD CURRENT,
FIGURE 3 CIRCUIT
toc18
1ms/div
STEADY-STATE SWITCHING WAVEFORMS,
5V OUTPUT, PWM MODE, NO LOAD,
FIGURE 3 CIRCUIT
toc19
MODE = SGND
VOUT
(AC)
20mV/div
VOUT
(AC)
VLX
10V/div
VLX
10V/div
ILX
500mA/div
ILX
2A/div
1μs/div
STEADY-STATE SWITCHING WAVEFORMS,
5V OUTPUT, PFM MODE, 25mA LOAD,
FIGURE 3 CIRCUIT
toc20
20mV/div
1μs/div
STEADY-STATE SWITCHING WAVEFORMS,
5V OUTPUT, DCM MODE, 25mA LOAD,
FIGURE 3 CIRCUIT
toc21
MODE = VCC
VOUT
(AC)
100mV/
div
VOUT
(AC)
VLX
10V/div
VLX
10V/div
500mA/div
ILX
200mA/div
ILX
20mV/div
MODE = OPEN
10μs/div
www.maximintegrated.com
1μs/div
Maxim Integrated │ 7
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Typical Operating Characteristics (continued)
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = 2 x 2.2µF, CVCC = 2.2µF, CBST = 0.1µF, CSS = 12,000pF, RT = MODE = open, TA = TJ
= -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise noted.)
5V OUTPUT, PWM MODE, FIGURE 3 CIRCUIT
(LOAD CURRENT STEPPED
FROM 1.75A TO 3.5A)
toc22
VOUT
(AC)
100mV/div
IOUT
2A/div
3.3V OUTPUT, PWM MODE, FIGURE 4 CIRCUIT
(LOAD CURRENT STEPPED
FROM 1.75A TO 3.5A)
toc23
VOUT
(AC)
100mV/div
IOUT
2A/div
40μs/div
100μs/div
5V OUTPUT, PWM MODE, FIGURE 3 CIRCUIT
(LOAD CURRENT STEPPED
FROM NO LOAD TO 1.75A)
toc24
VOUT
(AC)
IOUT
100mV/div
MODE = SGND
1A/div
3.3V OUTPUT, PWM MODE, FIGURE 4 CIRCUIT
(LOAD CURRENT STEPPED
FROM NO LOAD TO 1.75A) toc25
VOUT
(AC)
IOUT
100mV/div
1A/div
MODE = SGND
40μs/div
100μs/div
5V OUTPUT, PFM MODE, FIGURE 3 CIRCUIT
(LOAD CURRENT STEPPED
FROM 5mA TO 1.75A)
toc26
3.3V OUTPUT, PFM MODE, FIGURE 4 CIRCUIT
(LOAD CURRENT STEPPED
FROM 5mA TO 1.75A)
toc27
VOUT
(AC)
IOUT
100mV/div
1A/div
MODE = OPEN
2ms/div
www.maximintegrated.com
VOUT
(AC)
IOUT
100mV/div
1A/div
MODE = OPEN
2ms/div
Maxim Integrated │ 8
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Typical Operating Characteristics (continued)
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = 2 x 2.2µF, CVCC = 2.2µF, CBST = 0.1µF, CSS = 12,000pF, RT = MODE = open, TA = TJ
= -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise noted.)
5V OUTPUT, DCM MODE, FIGURE 3 CIRCUIT
(LOAD CURRENT STEPPED
FROM 50mA TO 1.75A)
toc28
VOUT
(AC)
3.3V OUTPUT, DCM MODE, FIGURE 4 CIRCUIT
(LOAD CURRENT STEPPED
FROM 50mA TO 1.75A)
toc29
100mV/div
VOUT
(AC)
1A/div
IOUT
100mV/div
1A/div
IOUT
MODE = VCC
MODE = VCC
200μs/div
200μs/div
OVERLOAD PROTECTION
5V OUTPUT, FIGURE 3 CIRCUIT
APPLICATION OF EXTERNAL CLOCK AT 700kHz
5V OUTPUT, FIGURE 3 CIRCUIT toc31
toc30
VOUT
2V/div
VLX
1A/div
IOUT
10V/div
VSYNC
2V/div
MODE = SGND
20ms/div
2μs/div
5V OUTPUT, 3.5A LOAD CURRENT
BODE PLOT, FIGURE 3 CIRCUIT toc32
toc33
140
60
140
50
120
50
120
40
100
40
80
30
PHASE
40
GAIN
0
-10
-20
-30
20
CROSSOVER
FREQUENCY = 48.4KHz,
PHASE MARGIN = 62.3°
-40
1K
10K
FREQUENCY (Hz)
www.maximintegrated.com
100K
PHASE
20
100
80
60
GAIN
10
40
0
20
0
-10
-20
-20
-40
-30
-60
-40
1K
PHASE (°)
10
60
PHASE (°)
20
GAIN (dB)
60
30
GAIN (dB)
3.3V OUTPUT, 3.5A LOAD CURRENT,
BODE PLOT, FIGURE 4 CIRCUIT
0
CROSSOVER
FREQUENCY = 52.7KHz,
PHASE MARGIN = 62.4°
-20
-40
-60
10K
100K
FREQUENCY (Hz)
Maxim Integrated │ 9
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
PGND
SGND
VCC
MODE
TOP VIEW
PGND
Pin Configuration
15
14
13
12
11
PGND 16
10
RT
LX 17
9
FB
8
CF
7
SS
6
SYNC
MAX17504
LX 18
LX 19
3
4
5
RESET
2
EN/UVLO
VIN
1
VIN
+
VIN
BST 20
TQFN
5mm × 5mm
* EXPOSED PAD (CONNECT TO SIGNAL GROUND).
Pin Description
PIN
NAME
FUNCTION
1, 2, 3
VIN
Power-Supply Input. 4.5V to 60V input supply range. Connect the VIN pins together. Decouple to PGND
with two 2.2µF capacitors; place the capacitors close to the VIN and PGND pins. Refer to the MAX17504
Evaluation Kit datasheet for a layout example.
4
EN/UVLO
Enable/Undervoltage Lockout. Drive EN/UVLO high to enable the output voltage. Connect to the center
of the resistor-divider between VIN and SGND to set the input voltage at which the MAX17504 turns on.
Pull up to VIN for always on operation.
5
RESET
6
SYNC
7
SS
Soft-Start Input. Connect a capacitor from SS to SGND to set the soft-start time.
8
CF
At switching frequencies lower than 500kHz, connect a capacitor from CF to FB. Leave CF open if the
switching frequency is equal to or more than 500kHz. See the Loop Compensation section for more
details.
9
FB
Feedback Input. Connect FB to the center tap of an external resistor-divider from the output to SGND to
set the output voltage. See the Adjusting Output Voltage section for more details.
10
RT
Connect a resistor from RT to SGND to set the regulator’s switching frequency. Leave RT open for the
default 500kHz frequency. See the Setting the Switching Frequency (RT) section for more details.
MODE
MODE configures the MAX17504 to operate in PWM, PFM or DCM modes of operation. Leave MODE
unconnected for PFM operation (pulse skipping at light loads). Connect MODE to SGND for constantfrequency PWM operation at all loads. Connect MODE to VCC for DCM operation. See the Mode
Selection (MODE) section for more details.
11
www.maximintegrated.com
Open-Drain RESET Output. The RESET output is driven low if FB drops below 92% of its set value.
RESET goes high 1024 clock cycles after FB rises above 95% of its set value.
The device can be synchronized to an external clock using this pin. See the External Frequency
Synchronization section for more details.
Maxim Integrated │ 10
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Pin Description (continued)
PIN
NAME
FUNCTION
12
VCC
13
SGND
Analog Ground
14, 15, 16
PGND
Power Ground. Connect the PGND pins externally to the power ground plane. Connect the SGND and
PGND pins together at the ground return path of the VCC bypass capacitor. Refer to the MAX17504
Evaluation Kit datasheet for a layout example.
17, 18, 19
LX
20
BST
—
EP
5V LDO Output. Bypass VCC with a 2.2µF ceramic capacitance to SGND.
Switching Node. Connect LX pins to the switching side of the inductor.
Boost Flying Capacitor. Connect a 0.1µF ceramic capacitor between BST and LX.
Exposed pad. Connect to the SGND pin. Connect to a large copper plane below the IC to improve heat
dissipation capability. Add thermal vias below the exposed pad. Refer to the MAX17504 Evaluation Kit
datasheet for a layout example.
Block Diagram
VCC
5V
BST
MAX17504
LDO
VIN
SGND
CURRENT-SENSE
LOGIC
EN/UVLO
LX
PWM/
PFM/
HICCUP
LOGIC
HICCUP
1.215V
RT
PGND
OSCILLATOR
SYNC
CF
FB
VCC
SS
SWITCHOVER
LOGIC
VBG = 0.9V
SLOPE
COMPENSATION
5µA
FB
HICCUP
www.maximintegrated.com
MODE
SELECTION
LOGIC
ERROR AMPLIFIER/
LOOP COMPENSATION
EN/UVLO
MODE
RESET
RESET
LOGIC
Maxim Integrated │ 11
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Detailed Description
The MAX17504 high-efficiency, high-voltage, synchronously
rectified step-down converter with dual integrated
MOSFETs operates over a 4.5V to 60V input. It delivers
up to 3.5A and 0.9V to 90% VIN output voltage. Built-in
compensation across the output voltage range eliminates
the need for external components. The feedback (FB)
regulation accuracy over -40°C to +125°C is ±1.1%.
The device features a peak-current-mode control
architecture. An internal transconductance error
amplifier produces an integrated error voltage at an
internal node that sets the duty cycle using a PWM
comparator, a high-side current-sense amplifier, and a
slope-compensation generator. At each rising edge of
the clock, the high-side MOSFET turns on and remains
on until either the appropriate or maximum duty cycle
is reached, or the peak current limit is detected. During
the high-side MOSFET’s on-time, the inductor current
ramps up. During the second half of the switching
cycle, the high-side MOSFET turns off and the low-side
MOSFET turns on. The inductor releases the stored
energy as its current ramps down and provides current
to the output.
PFM Mode Operation
PFM mode of operation disables negative inductor current
and additionally skips pulses at light loads for high
efficiency. In PFM mode, the inductor current is forced to
a fixed peak of 750mA every clock cycle until the output
rises to 102.3% of the nominal voltage. Once the output
reaches 102.3% of the nominal voltage, both the high-side
and low-side FETs are turned off and the device enters
hibernate operation until the load discharges the output to
101.1% of the nominal voltage. Most of the internal blocks
are turned off in hibernate operation to save quiescent
current. After the output falls below 101.1% of the nominal
voltage, the device comes out of hibernate operation,
turns on all internal blocks, and again commences the
process of delivering pulses of energy to the output until it
reaches 102.3% of the nominal output voltage.
The advantage of the PFM mode is higher efficiency at
light loads because of lower quiescent current drawn from
supply. The disadvantage is that the output-voltage ripple
is higher compared to PWM or DCM modes of operation
and switching frequency is not constant at light loads.
DCM Mode Operation
The device features a MODE pin that can be used
to operate the device in PWM, PFM, or DCM control
schemes. The device integrates adjustable-input
undervoltage lockout, adjustable soft-start, open RESET,
and external frequency synchronization features.
DCM mode of operation features constant frequency
operation down to lighter loads than PFM mode, by not
skipping pulses but only disabling negative inductor
current at light loads. DCM operation offers efficiency
performance that lies between PWM and PFM modes.
Mode Selection (MODE)
Linear Regulator (VCC)
The logic state of the MODE pin is latched when VCC
and EN/UVLO voltages exceed the respective UVLO
rising thresholds and all internal voltages are ready to
allow LX switching. If the MODE pin is open at power-up,
the device operates in PFM mode at light loads. If the
MODE pin is grounded at power-up, the device operates
in constant-frequency PWM mode at all loads. Finally,
if the MODE pin is connected to VCC at power-up, the
device operates in constant-frequency DCM mode at light
loads. State changes on the MODE pin are ignored during
normal operation.
PWM Mode Operation
In PWM mode, the inductor current is allowed to go negative. PWM operation provides constant frequency operation at all loads, and is useful in applications sensitive to
switching frequency. However, the PWM mode of operation gives lower efficiency at light loads compared to PFM
and DCM modes of operation.
www.maximintegrated.com
An internal linear regulator (VCC) provides a 5V nominal
supply to power the internal blocks and the low-side
MOSFET driver. The output of the linear regulator (VCC)
should be bypassed with a 2.2µF ceramic capacitor to
SGND. The MAX17504 employs an undervoltage lockout
circuit that disables the internal linear regulator when VCC
falls below 3.8V (typ).
Setting the Switching Frequency (RT)
The switching frequency of the MAX17504 can be
programmed from 200kHz to 2.2MHz by using a resistor
connected from RT to SGND. The switching frequency
(fSW) is related to the resistor connected at the RT pin
(RRT) by the following equation:
R RT ≅
21× 10 3
f SW
−
1.7
where RRT is in kΩ and fSW is in kHz. Leaving the RT pin
open causes the device to operate at the default switching
frequency of 500kHz. See Table 1 for RT resistor values
for a few common switching frequencies.
Maxim Integrated │ 12
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Table 1. Switching Frequency vs. RT
Resistor
SWITCHING FREQUENCY (kHz)
RT RESISTOR (kΩ)
500
OPEN
200
102
400
49.9
1000
19.1
2200
8.06
Operating Input Voltage Range
The minimum and maximum operating input voltages for
a given output voltage should be calculated as follows:
VIN(MIN) =
VOUT + (I OUT(MAX) × (R DCR + 0.15))
1- (f SW(MAX) × t OFF(MAX) )
+ (I OUT(MAX) × 0.175)
VIN(MAX) =
VOUT
f SW(MAX) × t ON(MIN)
where VOUT is the steady-state output voltage, IOUT(MAX)
is the maximum load current, RDCR is the DC resistance
of the inductor, fSW(MAX) is the maximum switching
frequency, tOFF(MAX) is the worst-case minimum switch
off-time (160ns), and tON(MIN) is the worst-case minimum
switch on-time (135ns).
External Frequency Synchronization (SYNC)
The internal oscillator of the MAX17504 can be synchronized
to an external clock signal on the SYNC pin. The external
synchronization clock frequency must be between 1.1
x fSW and 1.4 x fSW, where fSW is the frequency
programmed by the RT resistor. The minimum external
clock pulse-width high should be greater than 50ns. See
the RT and SYNC section in the Electrical Characteristics
table for details.
Overcurrent Protection/HICCUP Mode
The MAX17504 is provided with a robust overcurrent
protection scheme that protects the device under overload
and output short-circuit conditions. A cycle-by-cycle peak
current limit turns off the high-side MOSFET whenever
the high-side switch current exceeds an internal limit
of 5.1A (typ). A runaway current limit on the high-side
www.maximintegrated.com
switch current at 5.7A (typ) protects the device under
high input voltage, short-circuit conditions when there is
insufficient output voltage available to restore the inductor
current that was built up during the ON period of the
step-down converter. One occurrence of the runaway
current limit triggers a hiccup mode. In addition, if due
to a fault condition, feedback voltage drops to 0.58V
(typ) anytime after soft-start is complete, hiccup mode
is triggered. In hiccup mode, the converter is protected
by suspending switching for a hiccup timeout period of
32,768 clock cycles. Once the hiccup timeout period
expires, soft-start is attempted again. Note that when softstart is attempted under an overload condition, if feedback
voltage does not exceed 0.58V, the device switches at
half the programmed switching frequency. Hiccup mode
of operation ensures low power dissipation under output
short-circuit conditions.
RESET Output
The MAX17504 includes a RESET comparator to monitor
the output voltage. The open-drain RESET output requires
an external pullup resistor. RESET goes high (highimpedance) 1024 switching cycles after the regulator
output increases above 95% of the designed nominal
regulated voltage. RESET goes low when the regulator
output voltage drops to below 92% of the nominal
regulated voltage. RESET also goes low during thermal
shutdown.
Prebiased Output
When the MAX17504 starts into a prebiased output, both
the high-side and the low-side switches are turned off so
that the converter does not sink current from the output.
High-side and low-side switches do not start switching
until the PWM comparator commands the first PWM
pulse, at which point switching commences. The output
voltage is then smoothly ramped up to the target value in
alignment with the internal reference.
Thermal-Shutdown Protection
Thermal-shutdown protection limits total power dissipation
in the MAX17504. When the junction temperature of
the device exceeds +165°C, an on-chip thermal sensor
shuts down the device, allowing the device to cool. The
thermal sensor turns the device on again after the junction
temperature cools by 10°C. Soft-start resets during thermal
shutdown. Carefully evaluate the total power dissipation
(see the Power Dissipation section) to avoid unwanted
triggering of the thermal shutdown in normal operation.
Maxim Integrated │ 13
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Applications Information
saturation can occur only above the peak current-limit
value of 5.1A.
Input Capacitor Selection
The input filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on the input caused by the circuit’s switching.
The input capacitor RMS current requirement (IRMS) is
defined by the following equation:
=
IRMS I OUT(MAX) ×
VOUT × (VIN - VOUT )
VIN
where, IOUT(MAX) is the maximum load current. IRMS has
a maximum value when the input voltage equals twice
the output voltage (VIN = 2 x VOUT), so IRMS(MAX) =
IOUT(MAX)/2.
Choose an input capacitor that exhibits less than +10°C
temperature rise at the RMS input current for optimal
long-term reliability. Use low-ESR ceramic capacitors with
high ripple current capability at the input. X7R capacitors
are recommended in industrial applications for their
temperature stability. Calculate the input capacitance
using the following equation:
I OUT(MAX) × D × (1- D)
C IN =
η × f SW × ∆VIN
where D = VOUT/VIN is the duty ratio of the controller,
fSW is the switching frequency, ΔVIN is the allowable input
voltage ripple, and E is the efficiency.
In applications where the source is located distant from
the MAX17504 input, an electrolytic capacitor should
be added in parallel to the ceramic capacitor to provide
necessary damping for potential oscillations caused by
the inductance of the longer input power path and input
ceramic capacitor.
Inductor Selection
Three key inductor parameters must be specified for
operation with the MAX17504: inductance value (L),
inductor saturation current (ISAT), and DC resistance
(RDCR). The switching frequency and output voltage
determine the inductor value as follows:
L=
VOUT
f SW
where VOUT and fSW are nominal values.
Select a low-loss inductor closest to the calculated
value with acceptable dimensions and having the lowest
possible DC resistance. The saturation current rating
(ISAT) of the inductor must be high enough to ensure that
www.maximintegrated.com
Output Capacitor Selection
X7R ceramic output capacitors are preferred due to their
stability over temperature in industrial applications. The
output capacitors are usually sized to support a step load
of 50% of the maximum output current in the application,
so the output voltage deviation is contained to 3% of the
output voltage change. The minimum required output
capacitance can be calculated as follows:
C OUT=
1 I STEP × t RESPONSE
×
2
∆VOUT
t RESPONSE ≅ (
0.33
1
)
+
fC
f sw
where ISTEP is the load current step, tRESPONSE is the
response time of the controller, DVOUT is the allowable
output voltage deviation, fC is the target closed-loop
crossover frequency, and fSW is the switching frequency.
Select fC to be 1/9th of fSW if the switching frequency is
less than or equal to 500kHz. If the switching frequency is
more than 500kHz, select fC to be 55kHz.
Soft-Start Capacitor Selection
The MAX17504 implements adjustable soft-start operation
to reduce inrush current. A capacitor connected from
the SS pin to SGND programs the soft-start time. The
selected output capacitance (CSEL) and the output
voltage (VOUT) determine the minimum required soft-start
capacitor as follows:
CSS ≥ 28 x 10-6 x CSEL x VOUT
The soft-start time (tSS) is related to the capacitor
connected at SS (CSS) by the following equation:
tSS = CSS/(5.55 x 10-6)
For example, to program a 2ms soft-start time, a 12nF
capacitor should be connected from the SS pin to SGND.
VIN
R1
EN/UVLO
R2
SGND
Figure 1. Setting the Input Undervoltage Lockout
Maxim Integrated │ 14
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Setting the Input Undervoltage Lockout Level
The MAX17504 offers an adjustable input undervoltage
lockout level. Set the voltage at which MAX17504 turns
ON, with a resistive voltage-divider connected from VIN to
SGND. Connect the center node of the divider to EN/UVLO.
Choose R1 to be 3.3MI and then calculate R2 as follows:
R2 =
R1× 1.215
(VINU - 1.215)
where VINU is the voltage at which the MAX17504 is
required to turn ON. Ensure that VINU is higher than 0.8
x VOUT.
Loop Compensation
The MAX17504 is internally loop compensated. However,
if the switching frequency is less than 500kHz, connect a
0402 capacitor, C6, between the CF pin and the FB pin.
Use Table 2 to select the value of C6.
Adjusting Output Voltage
Set the output voltage with a resistive voltage-divider
connected from the positive terminal of the output
capacitor (VOUT) to SGND (see Figure 2). Connect the
center node of the divider to the FB pin. Use the following
procedure to choose the resistive voltage-divider values:
Calculate resistor R3 from the output to FB as follows:
R3 =
216 × 10 3
f C × C OUT
where R3 is in kI, crossover frequency fC is in kHz, and
output capacitor COUT is in µF. Choose fC to be 1/9th of
the switching frequency, fSW, if the switching frequency is
less than or equal to 500kHz. If the switching frequency is
more than 500kHz, select fC to be 55kHz.
Calculate resistor R4 from FB to SGND as follows:
R3 × 0.9
R4 =
(VOUT - 0.9)
Power Dissipation
Ensure that the junction temperature of the MAX17504
does not exceed +125°C under the operating conditions
specified for the power supply.
At a particular operating condition, the power losses that
lead to temperature rise of the part are estimated as
follows:
www.maximintegrated.com
Table 2. C6 Capacitor Value at Various
Switching Frequencies
SWITCHING FREQUENCY RANGE (kHz)
C6 (pF)
200 to 300
2.2
300 to 400
1.2
400 to 500
0.75
VOUT
R3
FB
R4
SGND
Figure 2. Setting the Output Voltage
(
1
PLOSS =
(POUT × ( - 1)) - I OUT 2 × R DCR
η
)
P=
OUT VOUT × I OUT
where POUT is the total output power, η is the efficiency
of the converter, and RDCR is the DC resistance of the
inductor. (See the Typical Operating Characteristics for more
information on efficiency at typical operating conditions).
For a multilayer board, the thermal performance metrics
for the package are given below:
θ JA = 30°C W
θ JC =2°C W
The junction temperature of the MAX17504 can be
estimated at any given maximum ambient temperature
(TA_MAX) from the equation below:
TJ_MAX
= T A _MAX + (θ JA × PLOSS )
If the application has a thermal management system
that ensures that the exposed pad of the MAX17504 is
maintained at a given temperature (TEP_MAX) by using
proper heat sinks, then the junction temperature of the
MAX17504 can be estimated at any given maximum
ambient temperature from the equation below:
T=
J_MAX TEP_MAX + (θ JC × PLOSS )
Maxim Integrated │ 15
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
PCB Layout Guidelines
currents must be kept separate. They should be connected
together at a point where switching activity is at a
minimum, typically the return terminal of the VCC bypass
capacitor. This helps keep the analog ground quiet.
The ground plane should be kept continuous/unbroken
as far as possible. No trace carrying high switching
current should be placed directly over any ground plane
discontinuity.
All connections carrying pulsed currents must be very
short and as wide as possible. The inductance of these
connections must be kept to an absolute minimum due to
the high di/dt of the currents. Since inductance of a current
carrying loop is proportional to the area enclosed by the
loop, if the loop area is made very small, inductance is
reduced. Additionally, small current loop areas reduce
radiated EMI.
PCB layout also affects the thermal performance of the
design. A number of thermal vias that connect to a large
ground plane should be provided under the exposed pad
of the part, for efficient heat dissipation.
A ceramic input filter capacitor should be placed close to the
VIN pins of the IC. This eliminates as much trace inductance
effects as possible and give the IC a cleaner voltage supply.
A bypass capacitor for the VCC pin also should be placed
close to the pin to reduce effects of trace impedance.
For a sample layout that ensures first pass success,
refer to the MAX17504 evaluation kit layout available at
www.maximintegrated.com.
When routing the circuitry around the IC, the analog
small-signal ground and the power ground for switching
VIN
(7.5V TO 60V)
EN/UVLO
VIN
VIN
BST
RT
LX
SYNC
MAX17504
MODE
C2
2.2µF
LX
LX
VCC
C8
2.2µF
C5
0.1µF
L1
10µH
VOUT
5V, 3.5A
C4
22µF
C9
22µF
R3
100kΩ
FB
SGND
CF
C1
2.2µF
VIN
R4
22.1kΩ
RESET
PGND
SS
PGND
PGND
C3
12000pF
fSW = 500kHz
L1 = SLF12575T-100M5R4-H
Figure 3. Typical Application Circuit for 5V Output
www.maximintegrated.com
Maxim Integrated │ 16
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
VIN
(5.5V TO 60V)
EN/UVLO
VIN
VIN
BST
RT
LX
SYNC
MAX17504
MODE
C2
2.2µF
LX
C8
2.2µF
C5
0.1µF
VOUT
3.3V, 3.5A
L1
6.8µH
C4
22µF
LX
VCC
C9
22µF
R3
82.5kΩ
FB
SGND
CF
C1
2.2µF
VIN
R4
30.9kΩ
RESET
SS
PGND
PGND
PGND
C3
12000pF
fSW = 500kHz
L1 = MSS1048-682NL
Figure 4. Typical Application Circuit for 3.3V Output
Ordering Information
PART
MAX17504ATP+
Package Information
PIN-PACKAGE
20 TQFN 5mm x 5mm
Note: All devices operate over the temperature range of -40ºC
to +125ºC, unless otherwise noted.
+Denotes a lead(Pb)-free/RoHS-compliant package.
Chip Information
PROCESS: BiCMOS
www.maximintegrated.com
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND PATTERN
NO.
20 TQFN-EP*
T2055+4
21-0140
90-0009
*EP = Exposed pad.
Maxim Integrated │ 17
MAX17504
4.5V–60V, 3.5A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
0
11/13
Initial release
1
2/14
Updated TOCs 32 and 33 and Typical Application Circuit Figures
DESCRIPTION
—
9, 16, 17
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim
reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
© 2014 Maxim Integrated Products, Inc. │ 18
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement