MAX17242, MAX17243
EVALUATION KIT AVAILABLE
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
General Description
The MAX17242/MAX17243 high-efficiency, synchronous
step-down DC-DC converters with integrated MOSFETs
operates over a 3.5V to 36V input voltage range, and
can operate in drop-out condition by running at 99% duty
cycle. The converters deliver up to 2A (MAX17242) and
3A (MAX17243) output current and generate fixed output
voltages of 3.3V/5V, along with the ability to program the
output voltage between 1V to 10V.
The devices use a current-mode-control architecture and
can be operated in the pulse-width modulation (PWM)
or pulse-frequency modulation (PFM) 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 operation. The low-resistance, on-chip
MOSFETs ensure high efficiency at full load and simplify
the layout.
The devices are available in a compact 20-pin (5mm x 5mm)
TQFN package with exposed pad. These parts are rated for
-40°C to +85°C operation.
Applications
●● Distributed Supply Regulation
●● Wall Transformer Regulation
●● General-Purpose Point-of-Load
Ordering Information appears at end of data sheet.
19-7767; Rev 0; 10/15
Benefits and Features
●● Eliminates External Components and Reduces Total Cost
• No Schottky-Synchronous Operation for High
Efficiency and Reduced Cost
• Simple external RC Compensation for Stable
Operation at Any Output Voltage
• All-Ceramic Capacitor Solution: Ultra-Compact
Layout with as Few as Eight External Components
• PGOOD Output and High-Voltage EN Input
Simplify Power Sequencing
●● Reduces Number of DC-DC Converters to Stock
• Pin Compatibility for 2A/3A Options
• Fixed Output Voltage with ±2% Accuracy (5V/3.3V)
or Externally Resistor Adjustable (1V to 10V) with
±1% FB Accuracy
• 220kHz to 2.2MHz Adjustable Frequency with
External Synchronization
●● Reduces Power Dissipation
• 93% Peak Efficiency
• Shutdown Feature Blocks Current Flow from Inputto-Output or Vice-Versa
• Less Than 5μA (typ) in Shutdown
• Low 15μA (typ) Quiescent Current in Standby
Mode
●● Operates Reliably
• 42V Input Voltage Transient Protection
• Fixed 8ms Internal Software Start Reduces Input
Inrush Current
• Cycle-by-Cycle Current Limit, Thermal Shutdown
with Automatic Recovery
• Reduced EMI Emission with Spread-Spectrum Control
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Typical Application Circuit/Block Diagram
2.2µH
2 x 22µF
LX
LX
LX
N.C.
FSYNC
0.1µF
VOUT = 3.3V/5V
AT 3A, 2.2MHz
FOSC
BST
OUT
PGND
12kΩ
MAX17242
MAX17243
FB
PGND
SPS
COMP
20.0kΩ
4.7µF
www.maximintegrated.com
SUPSW
SUPSW
EN
EP
2.2µF
AGND
1,000pF
SUP
PGOOD
BIAS
2.2µF
VBAT
Maxim Integrated │ 2
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Absolute Maximum Ratings
SUP, SUPSW, LX, EN to PGND............................-0.3V to +42V
SUP to SUPSW.....................................................-0.3V to +0.3V
BIAS to AGND..........................................................-0.3V to +6V
SPS, FOSC, COMP to AGND.................-0.3V to (VBIAS + 0.3V)
FSYNC, PGOOD, FB to AGND...............-0.3V to (VBIAS + 0.3V)
OUT to PGND........................................................-0.3V to +12V
BST to LX.................................................................-0.3V to +6V
AGND to PGND.....................................................-0.3V to +0.3V
Output Short-Circuit Duration.....................................Continuous
Continuous Power Dissipation (TA = +70°C)
20-Pin TQFN (derate 33.3mW/°C above +70°C) ...2666.7mW
Operating Temperature Range............................ -40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range............................. -65°C to +150°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
VSUP = VSUPSW = 14V, VEN = 14V, L1 = 2.2µH, CIN = 4.7µF, COUT = 44µF, CBIAS = 2.2µF, CBST = 0.1µF, RFOSC = 12kΩ, TA = TJ =
-40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
36
V
42
V
Supply Voltage
VSUP,
VSUPSW
Transient Event Supply Voltage
VSUP_LD
tLD < 1s
Supply Current (3.3V)
ISUP_
STANDBY
Standby mode, no load, VOUT = 3.3V,
VFSYNC = 0V
15
30
µA
Supply Current (5V)
ISUP_
STANDBY
Standby mode, no load, VOUT = 5V,
VFSYNC = 0V
20
35
µA
5
10
µA
3.5
Shutdown Supply Current
ISHDN
VEN = 0V
BIAS Regulator Voltage
VBIAS
VSUP = VSUPSW = 6V to 42V. IBIAS = 0
to 10mA
4.7
5
5.4
V
VBIAS rising
2.9
3.15
3.4
V
BIAS Undervoltage-Lockout
Hysteresis
400
500
mV
Thermal-Shutdown Threshold
175
°C
Thermal-Shutdown Threshold
Hysteresis
15
°C
BIAS Undervoltage Lockout
VUVBIAS
OUTPUT VOLTAGE
PWM-Mode Output Voltage
(Note 3)
VOUT_5V
VFB = VBIAS, 6V < VSUPSW < 36V,
fixed-frequency mode
4.9
5
5.1
V
PFM-Mode Output Voltage
(Note 4)
VOUT_
PFM_5V
No load, VFB = VBIAS, PFM mode
4.9
5
5.15
V
PWM-Mode Output Voltage
(Note 3)
VOUT_3.3V
VFB = VBIAS, 6V < VSUPSW < 36V,
fixed-frequency mode
3.23
3.3
3.37
V
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Maxim Integrated │ 3
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Electrical Characteristics (continued)
VSUP = VSUPSW = 14V, VEN = 14V, L1 = 2.2µH, CIN = 4.7µF, COUT = 44µF, CBIAS = 2.2µF, CBST = 0.1µF, RFOSC = 12kΩ, TA = TJ =
-40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PARAMETER
PFM-Mode Output Voltage
(Note 4)
SYMBOL
VOUT_
PFM_3.3V
CONDITIONS
No load, VFB = VBIAS, PFM mode
MIN
TYP
MAX
UNITS
3.23
3.3
3.4
V
Load Regulation
VFB = VBIAS, 30mA < ILOAD < 3A
0.5
%
Line Regulation
VFB = VBIAS, 6V < VSUPSW < 36V
0.02
%/V
IBST_ON
High-side MOSFET on,
VBST - VLX = 5V
1.5
mA
IBST_OFF
High-side MOSFET off,
VBST - VLX = 5V
1.5
µA
BST Input Current
LX Current Limit
ILX
MAX17243
3.75
5
6.25
MAX17242
2.5
3.33
4.16
LX Rise Time
VOUT = 5V, 3.3V
Spread Spectrum
Spread spectrum enabled
High-Side Switch OnResistance
FB Regulation Voltage
FB Line Regulation
Transconductance (from FB to
COMP)
FOSC
±3%
60
140
mΩ
High-side MOSFET off, VSUP = 36V,
VLX = 0V, TA = +25°C
1
5
µA
ILX = 0.5A, VBIAS = 5V
35
70
mΩ
Low-side MOSFET off, VSUP = 36V,
VLX = 36V, TA = +25°C
1
5
µA
IFB
TA = +25°C
20
100
nA
VFB
FB connected to an external resistive
divider, 6V < VSUPSW < 36V
1
1.01
V
RON_L
Low-Side Switch Leakage
Current
FB Input Current
ns
ILX = 0.5A, VBIAS = 5V
RON_H
High-Side Switch Leakage
Current
Low-Side Switch OnResistance
4
A
0.99
∆VLINE
6V < VSUPSW < 36V
0.02
%/V
gm
VFB = 1V, VBIAS = 5V
700
µS
Minimum On-Time
tON_MIN
Maximum Duty Cycle
DCMAX
98
RFOSC = 73.2kΩ
Oscillator Frequency
RFOSC = 12kΩ
80
ns
99
%
400
2.0
2.2
kHz
2.4
MHz
SYNC, EN, AND SPS LOGIC THRESHOLDS
External Input Clock Acquisition
time
1
tFSYNC
RFOSC = 12kΩ (Note 5)
External Input Clock Frequency
External Input Clock High
Threshold
VFSYNC_HI VFSYNC rising
External Input Clock Low
Threshold
VFSYNC_LO VFSYNC falling
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2.6
1.4
tSS
0.4
5.6
MHz
V
TA = +25°C
FSYNC Leakage Current
Soft-Start Time
1.8
Cycle
8
V
1
µA
12
ms
Maxim Integrated │ 4
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Electrical Characteristics (continued)
VSUP = VSUPSW = 14V, VEN = 14V, L1 = 2.2µH, CIN = 4.7µF, COUT = 44µF, CBIAS = 2.2µF, CBST = 0.1µF, RFOSC = 12kΩ, TA = TJ =
-40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PARAMETER
SYMBOL
Enable Input High Threshold
VEN_HI
Enable Input Low Threshold
VEN_LO
Enable Threshold-Voltage
Hysteresis
Enable Input Current
MIN
IEN
VSPS_HI
Spread-Spectrum Input Low
Threshold
VSPS_LO
ISPS
TYP
MAX
UNITS
0.6
V
2.4
V
0.2
VEN_HYS
Spread-Spectrum Input High
Threshold
Spread-Spectrum Input Current
CONDITIONS
TA = +25°C
0.1
V
1
2.0
TA = +25°C
µA
V
0.1
0.4
V
1
µA
POWER-GOOD AND OVERVOLTAGE-PROTECTION THRESOLDS
PGOOD Switching Level
VRISING
VFB rising, VPGOOD = high
93
95
97
VFALLING
VFB falling, VPGOOD = low
90
92.5
95
PGOOD Debounce Time
25
PGOOD Output Low Voltage
ISINK = 5mA
PGOOD Leakage Current
VOUT in regulation, TA = +25°C
Overvoltage Protection
Threshold
VOUT rising (Monitor FB pin)
107
VOUT falling (Monitor FB pin)
104
Note
Note
Note
Note
2:
3:
4:
5:
%VFB
µs
0.4
V
1
µA
%
Limits are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design.
Device not in dropout condition.
Guaranteed by design; not production tested.
Contact the factory for SYNC frequency outside the specified range.
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Maxim Integrated │ 5
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Typical Operating Characteristics
(VSUP = VSUPSW = 14V, VEN = 14V, VOUT = 5V, VFSYNC = 0V, RFOSC = 12kΩ, TA = +25°C, unless otherwise noted.)
100
fSW = 2.2MHz
VIN = 14V
80
3.3V
50
40
30
3.3V
5V
5V
PFM MODE
PWM
MODE
20
10
0
0.0001
0.01
0.1
1
70
3.3V
50
PFM MODE
30
LOAD REGULATION
0.001
SWITCHING FREQUENCY (MHz)
VOUT (V)
5.00
4.95
400kHz
4.90
4.85
4.80
0.0
0.5
1.0
1.5
2.0
2.5
2.26
2.24
0.5
1.0
VIN = 14V,
PWM MODE
toc07
2.20
2.18
2.16
2.14
VOUT = 3.3V
2.08
2.04
0.0
0.5
1.0
1.5
2.0
2.5
TEMPERATURE (°C)
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toc06
410
VOUT = 3.3V
405
400
395
390
385
0.0
0.5
1.0
1.5
2.0
2.5
3.0
ILOAD (A)
SWITCHING FREQUENCY
vs. RFOSC
toc08
SUPPLY CURRENT vs.
SUPPLY VOLTAGE
50
2.25
1.75
1.50
1.25
1.00
0.75
toc09
3.3V/2.2MHz PFM MODE
45
2.00
40
35
30
25
20
0.50
0.00
3.0
415
375
3.0
15
0.25
-40 -25 -10 5 20 35 50 65 80 95 110 125
2.5
380
2.50
VOUT = 5V
2.0
VIN = 14V,
PWM MODE
420
SUPPLY CURRENT (µA)
fSW vs. TEMPERATURE
1.5
fSW vs. LOAD CURRENT
425
toc05
ILOAD (A)
2.12
2.00
0.0
ILOAD (A)
VOUT = 3.3V
2.22
2.10
3.0
2.20
2.16
4.80
10
2.12
SWITCHING FREQUENCY (MHz)
SWITCHING FREQUENCY (MHz)
2.24
1
VIN = 14V,
PWM MODE
ILOAD (A)
2.28
0.1
fSW vs. LOAD CURRENT
2.30
5.15
5.05
0.01
LOAD CURRENT (A)
toc04
2.2MHz
400kHz
4.85
0
0.0001
2.28
5.10
5.00
4.95
10
10
2.2MHz
5.05
4.90
LOAD CURRENT (A)
5.20
PWM
MODE
5V
40
5.10
3.3V
toc03
VOUT = 5V, VIN = 14V,
PFM MODE
5.15
5V
60
LOAD REGULATION
5.20
20
COILCRAFT
XAL5030-222MEB
0.001
toc02
fSW = 400kHz,
VIN =14V
90
70
60
EFFICIENCY vs.
LOAD CURRENT
VOUT (V)
EFFICIENCY (%)
80
toc01
SWITCHING FREQUENCY (MHz)
90
EFFICIENCY vs.
LOAD CURRENT
EFFICIENCY (%)
100
12
42
72
RFOSC (kΩ)
102
132
10
6
12
18
24
30
36
SUPPLY VOLTAGE (V)
Maxim Integrated │ 6
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Typical Operating Characteristics (continued)
(VSUP = VSUPSW = 14V, VEN = 14V, VOUT = 5V, VFSYNC = 0V, RFOSC = 12kΩ, TA = +25°C, unless otherwise noted.)
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
10
toc10
50
3.3V/2.2MHz PFM MODE
9
SUPPLY CURRENT (µA)
SHUTDOWN CURRENT (µA)
7
6
5
4
3
40
35
30
25
20
2
15
1
6
12
18
24
30
10
36
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT
vs. TEMPERATURE
10
toc12
toc13
VIN = 14V, ILOAD = 0A, PWM MODE
5.08
8
SHUTDOWN CURRENT (µA)
BIAS VOLTAGE
vs. TEMPERATURE
5.10
3.3V/2.2MHz PFM MODE
9
5.06
7
5.04
VBIAS (V)
6
5
4
5.02
5.00
4.98
3
2
4.96
1
4.94
0
toc11
3.3V/2.2MHz PFM MODE
45
8
0
SUPPLY CURRENT
vs. TEMPERATURE
4.92
-40 -25 -10 5 20 35 50 65 80 95 110 125
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
TEMPERATURE (°C)
VOUT vs. VIN
5.20
5V/2.2MHz, ILOAD = 0A, PWM MODE
5.15
5.05
5.05
VOUT (V)
VOUT (V)
5.10
5.00
4.95
toc15
5V/2.2MHz
PWM MODE
ILOAD = 0A
5.15
5.10
5.00
4.95
4.90
4.90
4.85
4.85
4.80
VOUT vs. VIN
5.20
toc14
6
12
18
24
VIN (V)
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30
36
4.80
6
12
18
24
30
VIN (V)
36
42
Maxim Integrated │ 7
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Typical Operating Characteristics (continued)
(VSUP = VSUPSW = 14V, VEN = 14V, VOUT = 5V, VFSYNC = 0V, RFOSC = 12kΩ, TA = +25°C, unless otherwise noted.)
FULL-LOAD
STARTUP BEHAVIOR
SLOW VIN
RAMP BEHAVIOR
toc16
10V/div
0
VIN
100V/div
5V/div
VOUT
0
1V/div
1A/div
ILOAD
0
5V/div
VPGOOD
0
0
5V/div
0
VOUT
1V/div
10V/div
VLX
0
2A/div
0
5V/div
0
ILOAD
VPGOOD
5V/div
VFSYNC
0
4s
LINE TRANSIENT
toc19
10V/div
VIN
toc18
10V/div
VIN
100nF
2ms
DIPS AND DROPS
SYNC FUNCTION
toc17
200ns
5V/2.2MHz
VIN
TRANSIENT
toc20
toc21
2V/div
0
5V/div
VOUT
0
VLX
10V/div
0
VPGOOD
5V/div
VIN
10V/div
0
VOUT
2V/div
VPGOOD
VOUT
5V/div
0
5V/div
0
0
10ms
100ms
400ms
LOAD TRANSIENT
(PWM MODE)
SHORT CIRCUIT
(PWM MODE)
toc22
toc23
VOUT
500mV/div
(ACCOUPLED)
VOUT
1A/div
2V/div
0
5A/div
ILX
0
5V/div
VPGOOD
IOUT
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0
0
100µs
20ms
Maxim Integrated │ 8
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
BST
PGND
PGND
SPS
PGOOD
Pin Configuration
1
1
1
1
11
LX 16
1
SUP
SUPSW
LX 1
1
1
LX 1
SUPSW
EN
N.C. 1
FSYNC
EP
6
AGND
EP
BIAS
COMP
FB
OUT
FOSC
1
EXPOSED PAD
Pin Description
PIN
NAME
1
FOSC
2
OUT
3
FB
Feedback Input. Connect an external resistive divider from OUT to FB and AGND to set the output
voltage. Connect to BIAS to set the output voltage to 5V or 3.3V.
4
COMP
Error Amplifier Output. Connect an RC network from COMP to AGND for stable operation. See the
Compensation Network section for more details.
5
BIAS
6
AGND
7
EN
SUP Voltage-Compatible Enable Input. Drive EN low to PGND to disable the devices. Drive EN high to
enable the devices.
8, 9
SUPSW
Internal High-Side Switch Supply Input. SUPSW provides power to the internal switch. Bypass SUPSW
to PGND with a 0.1µF and 4.7µF ceramic capacitors.
10
SUP
Voltage Supply Input. SUP powers up the internal linear regulator. Bypass SUP to PGND with a 2.2µF
ceramic capacitor.
11
PGOOD
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FUNCTION
Resistor-Programmable Switching Frequency Setting Control Input. Connect a resistor from FOSC to
AGND to set the switching frequency.
Switching Regulator Output. OUT also provides power to the internal circuitry when the output voltage of
the converter is set between 3V to 5V during standby mode.
Linear Regulator Output. BIAS powers up the internal circuitry. Bypass with a minimum of 2.2µF ceramic
capacitor to AGND.
Analog Ground
Open-Drain, PGOOD Output. PGOOD asserts when VOUT is above 95% regulation point. PGOOD goes
low to AGND when VOUT is below 92% regulation point.
Maxim Integrated │ 9
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Pin Description (continued)
PIN
NAME
12
SPS
13,14
PGND
15
BST
16–18
LX
19
N.C.
20
FSYNC
—
EP
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FUNCTION
Spread-Spectrum Pin. Pull high for spread spectrum on and low to AGND for spread spectrum off.
Power Ground
High-Side Driver Supply. Connect a 0.1µF capacitor between LX and BST for proper operation.
Inductor Switching Node
No Connection
Synchronization Input. The devices synchronize to an external signal applied to FSYNC. Connect
FSYNC to AGND to enable PFM mode operation. Connect to BIAS or to an external clock to enable
fixed-frequency, forced-PWM mode operation.
Exposed Pad. Connect EP to a large-area contiguous copper ground plane for effective power
dissipation. Do not use as the only IC ground connection. EP must be connected to PGND.
Maxim Integrated │ 10
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
MAX17242
MAX17243
PGOOD
OUT
PGOOD HIGH LEVEL
PGOOD LOW LEVEL
PGOOD
COMPARATOR
BIAS
SUP
INTERNAL BIAS
REGULATOR
SWITCHOVER
LOGIC
FEEDBACK
SELECT
LOGIC
FB
EN
PV
SUPSW
PV
BST
AGND
INTERNAL
SOFT-START
PWM
VREF = 1V
LX
CONTROL
LOGIC
PV
EAMP
COMP
SPS
PGND
CLK
FOSC
SPREAD
SPECTRUM
ON/OFF
FSYNC
FSYNC
SELECT
LOGIC
OSCILLATOR
EXTERNAL
CLOCK
CONNECTED HI
(PWM MODE )
CONNECTED LO
(PFM MODE )
SLOPE COMP
LOGIC
CURRENT -LIMIT
THRESHOLD
ZEROCROSSING
COMPARATOR
LX
Figure 1. Internal Block Diagram
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Maxim Integrated │ 11
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Detailed Description
The MAX17242/MAX17243 are 2A/3A current-mode stepdown converters with integrated high-side and lowside MOSFETs. The low-side MOSFET enables fixedfrequency, forced-PWM operation in light-load applications.
The devices operate with input voltages from 3.5V to
36V while using only 15µA quiescent current at no load.
The switching frequency is resistor programmable from
220kHz to 2.2MHz and can be synchronized to an external
clock. The devices’ output voltage is available as 5V/3.3V
fixed or adjustable from 1V to 10V. The wide input voltage
range, along with its ability to operate at 99% duty cycle
during undervoltage transients, makes the devices ideal
for many applications.
In light-load applications, a logic input (FSYNC) allows
the devices to operate either in PFM mode for reduced
current consumption, or fixed-frequency, forced-PWM
mode to eliminate frequency variation and help minimize
EMI. Protection features include cycle-by-cycle current
limit, and thermal shutdown with automatic recovery.
Wide Input Voltage Range
The devices include two separate supply inputs (SUP and
SUPSW) specified for a wide 3.5V to 36V input voltage
range. VSUP provides power to the device and VSUPSW
provides power to the internal switch. Often in a system,
severe transient conditions can cause the voltage at SUP
and SUPSW pins to drop below the programmed output
voltage. In a system where severe transient conditions
can cause the voltage at the SUP and SUPSW pins to
drop below the programmed output voltage. Under such
conditions, the devices operate in a high duty-cycle mode
to facilitate minimum dropout from input to output.
Maximum Duty-Cycle Operation
The devices have a maximum duty cycle of 98%
(typ). The IC monitors the off time (time for which
the low-side FET is on) in both PWM and PFM
modes during every switching cycle every switching
cycle. Once the off time of 100ns (typ) is detected
continuously for 12µs, the low-side FET is forced on for
150ns (typ) every 12µs. The input voltage at which the
devices enter dropout changes depending on the input
voltage, output voltage, switching frequency, load current,
and the efficiency of the design.
The input voltage at which the devices enter dropout can
be approximated as:
VSUP =
VOUT + (I OUT × R ON_H )
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Note: The equation above does not take into account the
efficiency and switching frequency but is a good first-order
approximation. Use the RON_H number from the max
column in the Electrical Characteristics table.
Linear Regulator Output (BIAS)
The devices include a 5V linear regulator (VBIAS) that
provides power to the internal circuit blocks. Connect a
2.2µF ceramic capacitor from BIAS to AGND.
Power-Good Output (PGOOD)
The devices feature an open-drain power-good output
(PGOOD). PGOOD asserts when VOUT rises above 95%
of its regulation voltage. PGOOD deasserts when VOUT
drops below 92.5% of its regulation voltage. Connect
PGOOD to BIAS with a 10kΩ resistor to AGND.
Synchronization Input (FSYNC)
FSYNC is a logic-level input useful for operating-mode
selection and frequency control. Connecting FSYNC to
BIAS or to an external clock enables fixed-frequency,
forced-PWM operation. Connecting FSYNC to AGND
enables PFM-mode operation.
The external clock frequency at FSYNC can be higher
or lower than the internal clock by 20%. If the external
clock frequency is greater than 120% of the internal clock,
contact the factory applications team to verify the design.
The devices synchronize to the external clock in two
cycles. When the external clock signal at FSYNC is
absent for more than two clock cycles, the devices use
the internal clock.
System Enable (EN)
An enable control input (EN) activates the devices
from their low-power shutdown mode. EN is rated up
to 42V, allowing direct connection to SUP or through a
resistor divider to set the desired input undervoltagelockout threshold.
EN turns on the internal regulator. Once VBIAS is above
the internal lockout threshold, VUVBIAS = 3.15V (typ),
the converter activates and the output voltage ramps up
within 8ms.
A logic-low to PGND at EN shuts down the device. During
shutdown, the internal linear regulator and gate drivers
turn off. Shutdown is the lowest power state and reduces
the quiescent current to 5µA (typ). Drive EN high to bring
the devices out of shutdown.
0.98
Maxim Integrated │ 12
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Spread-Spectrum Option
The spread spectrum can be enabled on the device
using a pin. When the SPS pin is pulled high the spread
spectrum is enabled and the operating frequency is varied
±3% centered on FOSC. The modulation signal is a triangular wave with a period of 110μs at 2.2MHz. Therefore,
FOSC ramps down 3% and back to 2.2MHz in 110μs and
also ramps up 3% and back to 2.2MHz in 110μs. The
cycle repeats.
For operations at FOSC values other than 2.2MHz, the
modulation signal scales proportionally (e.g., at 400kHz,
the 110μs modulation period increases to 110μs x
2.2MHz/0.4MHz = 550μs).
The internal spread spectrum is disabled if the devices
are synchronized to an external clock. However, the
devices do not filter the input clock on the FSYNC pin and
pass any modulation (including spread spectrum) present
on the driving external clock. Drive the SPS pin low to
AGND to disable spread spectrum.
Applications Information
Setting the Output Voltage
Connect FB to BIAS for a fixed +5V/3.3V output voltage.
See Ordering Information. To set the output to other voltages
between 1V and 10V, connect a resistive divider from
output (OUT) to FB to AGND (Figure 2). Select RFB2 (FB
to AGND resistor) less than or equal to 500kΩ. Calculate
RFB1 (OUT to FB resistor) with the following equation:
 V
 
R FB1 = R FB2  OUT  - 1
 VFB  
where VFB = 1V (see the Electrical Characteristics
table).
VOUT
Internal Oscillator (FOSC)
The switching frequency (fSW) is set by a resistor (RFOSC)
connected from FOSC to AGND. For example, a 400kHz
switching frequency is set with RFOSC = 73.2kΩ. Higher
frequencies allow designs with lower inductor values and
less output capacitance. Consequently, peak currents and
I2R losses are lower at higher switching frequencies, but
core losses, gate-charge currents, and switching losses
increase. See Typical Operating Characteristics section.
MAX17242
MAX17243
RFB1
FB
RFB2
Overtemperature Protection
Thermal overload protection limits the total power
dissipation in the device. When the junction temperature
exceeds 175°C (typ), an internal thermal sensor shuts
down the internal bias regulator and the step-down
converter, allowing the IC to cool. The thermal sensor
turns on the IC again after the junction temperature cools
by 15°C.
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Figure 2. Adjustable Output-Voltage Setting
Maxim Integrated │ 13
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Forced-PWM and PFM Modes
In PWM mode of operation, the devices switch at
a constant frequency with variable on-time. In PFM
mode of operation, the converter’s switching frequency
is load dependent. At higher load current, the switching
frequency does not change and the operating mode is
similar to the PWM mode. PFM mode helps improve
efficiency in light-load applications by allowing the
converters to turn on the high-side switch only when the
output voltage falls below a set threshold. As such, the
converters do not switch MOSFETs on and off as often
as in the PWM mode. Consequently, the gate charge
and switching losses are much lower in PFM mode. The
operation mode of the device is set by FSYNC pin.
Inductor Selection
Three key inductor parameters must be specified for
operation with the devices: inductance value (L), inductor
saturation current (ISAT), and DC resistance (RDCR). To
select inductor value, the ratio of inductor peak-to-peak AC
current to DC average current (LIR) must be selected first.
A good compromise between size and loss is a 30% peakto-peak ripple current to average-current ratio (LIR = 0.3).
The switching frequency, input voltage, output voltage, and
selected LIR then determine the inductor value as follows:
L=
Choose an input capacitor that exhibits less than +10°C
self-heating temperature rise at the RMS input current for
optimal long-term reliability.
The input-voltage ripple is comprised of ΔVQ (caused
by the capacitor discharge) and ΔVESR (caused by the
ESR of the capacitor). Use low-ESR ceramic capacitors
with high ripple-current capability at the input. Assume
the contribution from the ESR and capacitor discharge
equal to 50%. Calculate the input capacitance and ESR
required for a specified input voltage ripple using the
following equations:
ESR IN =
where:
(V
- VOUT ) × VOUT
∆IL = SUP
VSUP × f SW × L
and:
I
× D(1- D)
C IN = OUT
∆VQ × f SW
(VSUP − VOUT ) × VOUT
VSUP × f SW × I OUT × LIR
where VSUP, VOUT, and IOUT are typical values (so that
efficiency is optimum for typical conditions). The switching frequency is set by RFOSC (see TOC 8 in the Typical
Operating Characteristics section).
Input Capacitor
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 ILOAD(MAX) ×
VOUT x(VSUP - VOUT )
VSUP
IRMS has a maximum value when the input voltage
equals twice the output voltage:
VSUP= 2 × VOUT
therefore:
IRMS =
www.maximintegrated.com
ILOAD(MAX)
VSUP
∆VESR
∆I
I OUT + L
2
D=
VOUT
VSUPSW
where: IOUT is the maximum output current and D is the
duty cycle.
Output Capacitor
The output filter capacitor must have low enough equivalent
series resistance (ESR) to meet output-ripple and loadtransient requirements. The output capacitance must be high
enough to absorb the inductor energy while transitioning from
full-load to no-load conditions without tripping the overvoltagefault protection. When using high-capacitance, low-ESR
capacitors, the filter capacitor’s ESR dominates the outputvoltage ripple, so the size of the output capacitor depends on
the maximum ESR required to meet the output-voltage ripple
(VRIPPLE(P-P)) specifications:
VRIPPLE(P-P) =
ESR × ILOAD(MAX) × LIR
The actual capacitance value required relates to the
physical size needed to achieve low ESR, as well as
to the chemistry of the capacitor technology. Thus, the
capacitor is usually selected by ESR and voltage rating
rather than by capacitance value.
Maxim Integrated │ 14
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
When using low-capacity filter capacitors, such as ceramic
capacitors, size is usually determined by the capacity needed
to prevent voltage droop and voltage rise from causing
problems during load transients. Generally, once enough
capacitance is added to meet the overshoot requirement,
undershoot at the rising load edge is no longer a problem.
However, low-capacity filter capacitors typically have highESR zeros that can affect the overall stability.
In a current-mode step-down converter, the output capacitor,
its ESR, and the load resistance introduce a pole at the
following frequency:
f pMOD =
The output capacitor and its ESR also introduce a zero at:
f zMOD =
Compensation Network
The devices use an internal transconductance error
amplifier with its inverting input and its output available to
the user for external frequency compensation. The output
capacitor and compensation network determine the loop
stability. The inductor and the output capacitor are chosen
based on performance, size, and cost. Additionally, the
compensation network optimizes the control-loop stability.
The converter uses a current-mode-control scheme that
regulates the output voltage by forcing the required
current through the external inductor. The devices use
the voltage drop across the high-side MOSFET to sense
inductor current. Current-mode control eliminates the
double pole in the feedback loop caused by the inductor
and output capacitor, resulting in a smaller phase shift
and requiring less elaborate error-amplifier compensation
than voltage-mode control. Only a simple single series
resistor (RC) and capacitor (CC) are required to have a
stable, high-bandwidth loop in applications where ceramic
capacitors are used for output filtering (see Figure 3). For
other types of capacitors, due to the higher capacitance
and ESR, the frequency of the zero created by the capacitance
and ESR is lower than the desired closed-loop crossover
frequency. To stabilize a nonceramic output-capacitor
loop, add another compensation capacitor (CF) from
COMP to ground to cancel this ESR zero.
The basic regulator loop is modeled as a power modulator,
output feedback divider, and an error amplifier. The
power modulator has a DC gain set by gm × RLOAD,
with a pole and zero pair set by RLOAD, the output
capacitor (COUT), and its ESR. The following equations
help to approximate the value for the gain of the power
modulator (GAINMOD(dc)), neglecting the effect of the
ramp stabilization. Ramp stabilization is necessary when
the duty cycle is above 50% and is internally done for the
devices:
1
2π × C OUT × R LOAD
1
2π × ESR × C OUT
When COUT is composed of “n” identical capacitors
in parallel, the resulting COUT = n × COUT(EACH), and
ESR = ESR(EACH)/n. Note that the capacitor zero for a
parallel combination of alike capacitors is the same as
for an individual capacitor.
The feedback voltage-divider has a gain of GAINFB =
VFB/VOUT, where VFB is 1V (typ).
The transconductance error amplifier has a DC gain
of GAINEA(DC) = gm_EA × ROUT_EA, where gm_EA is
the error amplifier transconductance, which is 700µS
(typ), and ROUT_EA is the output resistance of the error
amplifier (50MΩ).
VOUT
R1
gm
COMP
R2
REF
RC
CF
CC
GAINMOD(dc)
= g mc × R LOAD
where RLOAD = VOUT/IOUT(MAX) in Ω and gmc = 3S.
www.maximintegrated.com
Figure 3. Compensation Network
Maxim Integrated │ 15
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
A dominant pole (fdpEA) is set by the compensation capacitor
(CC) and the amplifier output resistance (ROUT_EA). A
zero (fZEA) is set by the compensation resistor (RC) and
the compensation capacitor (CC). There is an optional
pole (fPEA) set by CF and RC to cancel the output capacitor
ESR zero if it occurs near the crossover frequency (fC,
where the loop gain equals 1 (0dB)). Thus:
f zEA =
f pdEA =
1
2π × C C × R C
1
2π × C C × (R OUT,EA + R C )
1
f pEA =
2π × C F × R C
The loop-gain crossover frequency (fC) should be set
below 1/5 of the switching frequency and much higher
than the power-modulator pole (fpMOD)
Set the error-amplifier compensation zero formed by RC
and CC (fzEA) at the fpMOD. Calculate the value of CC a
follows:
1
CC =
2π × f pMOD × R C
If fzMOD is less than 5 x fC, add a second capacitor (CF)
from COMP to GND and set the compensation pole
formed by RC and CF (fpEA) at the fzMOD. Calculate the
value of CF as follows:
1
CF =
2π × f zMOD × R C
As the load current decreases, the modulator pole
also decreases; however, the modulator gain increases
accordingly and the crossover frequency remains the
same. For the case where fzMOD is less than fC:
The power-modulator gain at fC is:
GAIN
=
MOD(fC) GAINMOD(dc) ×
f pMOD
f zMOD
The error-amplifier gain at fC is:
The total loop gain as the product of the modulator gain,
the feedback voltage divider gain, and the error amplifier
gain at fC should be equal to 1. So:
GAINMOD(fC) ×
VFB
× GAINEA(fC) =
1
VOUT
For the case where fzMOD is greater than fC:
GAINEA(fC)
= g m,EA × R C
Therefore:
V
GAINMOD(fC) × FB × g m,EA × R C =
1
VOUT
Solving for RC:
RC =
VOUT
g m,EA × VFB × GAINMOD(fC)
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f
GAINEA(fC)
= g m,EA × R C × zMOD
fC
Therefore:
GAINMOD(fC) ×
f
VFB
× g m,EA × R C × zMOD =
1
VOUT
fC
Solving for RC:
RC =
VOUT × f C
g m,EA × VFB × GAINMOD(fC) × f zMOD
Set the error-amplifier compensation zero formed by RC
and CC at the fpMOD (fzEA = fpMOD).
CC =
1
2π × f pMOD × R C
If fzMOD is less than 5 × fC, add a second capacitor CF
from COMP to AGND. Set fpEA = fzMOD and calculate
CF as follows:
1
CF =
2π × f zMOD × R C
Maxim Integrated │ 16
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching
losses and clean, stable operation. Use a multilayer board
whenever possible for better noise immunity and power
dissipation. Follow these guidelines for good PC board
layout:
1) Use a large contiguous copper plane under the
device package. Ensure that all heat-dissipating
components have adequate cooling. The bottom pad
of the devices must be soldered down to this copper
plane for effective heat dissipation and getting the full
power out of the devices. Use multiple vias or a single
large via in this plane for heat dissipation
2) Isolate the power components and high current path
from the sensitive analog circuitry. This is essential to
prevent any noise coupling into the analog signals.
3) Keep the high-current paths short, especially at the
PGND terminals. This practice is essential for stable,
jitter-free operation. The high current path comprising
of input capacitor, high-side FET, inductor, and the
output capacitor should be as short as possible.
4) Keep the power traces and load connections short.
This practice is essential for high efficiency. Use
thick copper PCBs (2oz vs. 1oz) to enhance full-load
efficiency.
5) The analog signal lines should be routed away from
the high-frequency planes. This ensures integrity of
sensitive signals feeding back into the IC.
6) The ground connection for the AGND and PGND
section should be close to the IC. This keeps the
ground current loops to a minimum. In cases where
only one ground is used, adequate isolation between
analog return signals and high-power signals must be
maintained.
Ordering Information
PART
VOUT ADJUSTABLE
MAX OPERATING
VOUT FIXED
(FB TIED TO RESISTOR
(FB TIED TO BIAS
CURRENT
DIVIDER)
TEMP TANGE
PIN-PACKAGE
MAX17242ETPA+
1V TO 10V
5V
2A
-40°C to +85°C
20 TQFN-EP*
MAX17242ETPB+
1V TO 10V
3.3V
2A
-40°C to +85°C
20 TQFN-EP*
MAX17243ETPA+
1V TO 10V
5V
3A
-40°C to +85°C
20 TQFN-EP*
MAX17243ETPB+
1V TO 10V
3.3V
3A
-40°C to +85°C
20 TQFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Chip Information
PROCESS: BiCMOS
www.maximintegrated.com
Package Information
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+4C
21-0140
90-0010
Maxim Integrated │ 17
MAX17242/MAX17243
3.5V–36V, 2A/3A, Synchronous Buck Converter
with 15µA Quiescent Current and Reduced EMI
Revision History
REVISION
NUMBER
REVISION
DATE
0
10/15
DESCRIPTION
Initial release
PAGES
CHANGED
—
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated 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.
© 2015 Maxim Integrated Products, Inc. │ 18
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