Multimode PA Step-Down Converter with Linear

Multimode PA Step-Down Converter with Linear
EVALUATION KIT AVAILABLE
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
General Description
The MAX8989 step-down converter is optimized for powering the power amplifier (PA) in multistandard handsets
such as LTE, WCDMA, GSM, and EDGE. The device
integrates a high-efficiency PWM step-down converter for
medium- and low-power transmission with an 85mI (typ)
low dropout (LDO) bypass regulator, in parallel with the
step-down converter, enabling high-power transmission.
The IC uses an analog input driven by an external DAC
to control the output voltage linearly for continuous PA
power adjustment. The bypass LDO powers the PA
directly from the battery during high-power transmission
or in case of insufficient headroom between the input and
programmed output. The bypass LDO is enabled when
the output voltage is greater than 1.0V. In the case where
the output current exceeds the step-down converter current limit, the bypass LDO provides supplementary current to the output, ensuring a stable output voltage. The
bypass LDO also provides a smooth transition between
step-down regulation and operation in dropout.
The IC is available in a 9-bump, 1.6mm x 1.6mm WLP
package (0.69mm max height).
Applications
Features
S PA Step-Down Converter
25µs (typ) Settling Time for 0.4V to 3.2V Output
Voltage Change
Dynamic Output Voltage Setting from 0.4V to VIN
85mI pFET and 100% Duty Cycle for Low
Dropout
2MHz Switching Frequency
Low Output Voltage Ripple
2% Output Voltage Accuracy Over Load, Line,
and Temperature
Tiny External Components
S 2.5A Output Current Capability
S Simple Logic On/Off Control
S Low 0.1µA Shutdown Current
S 2.7V to 5.5V Supply Voltage Range
S Thermal Overload Protection
S 1.6mm x 1.6mm WLP Package (0.69mm max
Height)
LTE, WCDMA, GSM, and EDGE Cell Phones/
Smartphones
Typical Operating Circuit
Ordering Information
PART
MAX8989EWL+T
TEMP RANGE
PIN-PACKAGE
-40NC to +85NC
9 WLP
0.5mm pitch
+Denotes lead(Pb)-free/RoHS-compliant package.
T = Tape and reel. This device has a minimum order increment
of 2500 pieces.
BATTERY
INPUT
2.7V TO
5.5V
MAX8989
IN2
OUT
OUTPUT
0.4V TO
VBATT
UP TO
2.5A
4.7µF
BYPASS LDO
IN1
4.7µF
ANALOG
CONTROL
0.2V TO
2.1V
OFF
FPWM
REFIN
1000pF
STEP-DOWN
LOGIC
LX
4.7µH
4 x 4.7µF
ON
SKIP
EN
SKIP
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
PGND
AGND
19-5489; Rev 1; 1/11
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
ABSOLUTE MAXIMUM RATINGS
IN1, IN2, SKIP, EN, REFIN to AGND.....................-0.3V to +6.0V
OUT to AGND............................................ -0.3V to (VIN2 + 0.3V)
IN1 to IN2..............................................................-0.3V to +0.3V
PGND to AGND.....................................................-0.3V to +0.3V
IN1, IN2, OUT, LX Current (Note 1).................................. 1ARMS
OUT Short Circuit to AGND........................................Continuous
Continuous Power Dissipation (TA = +70NC)
9-Bump WLP 0.5mm Pitch
(derate 14.1mW/NC above +70NC)...................................1.1W
Operating Temperature Range........................... -40NC to +85NC
Junction to Ambient
Thermal Resistance (BJA) (Note 2)...............................71NC/W
Operating Temperature Range........................... -40NC to +85NC
Junction Temperature (TJMAX)........................................+150NC
Storage Temperature Range............................. -65NC to +150NC
Soldering Temperature (reflow).......................................+260NC
Note 1: LX has internal clamp diodes to PGND and IN1. Applications that forward bias this diode should take care not to exceed the
power dissipation limits of the device.
Note 2: 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.
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.
ELECTRICAL CHARACTERISTICS
(VIN1 = VIN2 = VSKIP = VEN = 3.6V, VREFIN = 0.9V, TA = -40NC to +85NC. Typical values are at TA = +25NC, unless otherwise noted.)
(Note 3)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
5.5
V
2.63
2.70
V
INPUT SUPPLY
Input Voltage Range (VIN)
VIN1 = VIN2
2.7
Input Undervoltage Threshold
VIN2 rising, 180mV typical hysteresis
2.52
VEN = VIN_, IOUT = 0A, SKIP = AGND, switching
No-Load Supply Current
VEN = VIN_, IOUT = 0A, VSKIP = VIN_,
VREFIN = 0.35V, no switching
Shutdown Supply Current
VEN = 0V
3
mA
0.115
TA = +25NC
0.1
TA = +85NC
0.1
1
FA
THERMAL PROTECTION
Thermal Shutdown
+160
TJ rising, 20NC typical hysteresis
NC
LOGIC CONTROL
EN and SKIP Logic-Input High Voltage
1.3
V
EN and SKIP Logic-Input Low Voltage
0.4
EN Internal Pulldown Resistor
SKIP Logic-Input Current
800
VIL = 0V, VIH = 5.5V
TA = +25NC
0.01
TA = +85NC
0.1
V
kI
1
FA
POWER-UP TIMING (Figure 2)
Time Delay from EN Until LX Starts
Switching (tEN_BUCK)
2 62
130
Fs
Maxim Integrated
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
ELECTRICAL CHARACTERISTICS (continued)
(VIN1 = VIN2 = VSKIP = VEN = 3.6V, VREFIN = 0.9V, TA = -40NC to +85NC. Typical values are at TA = +25NC, unless otherwise noted.)
(Note 3)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
1.7
V
REFIN
Common-Mode Range
REFIN to OUT Gain
0.2
VREFIN = 0.32V, ILX = 0A
1.89
2
2.11
VREFIN = 1.32V, ILX = 0A
1.96
2.0
2.04
V/V
Input Resistance
800
kI
REFIN Source Current
30
FA
Forced Dropout Mode Threshold
Above this threshold, the MAX8989 is forced
into dropout mode, no hysteresis is implemented
1.80
1.95
2.10
V
LINEAR BYPASS
On-Resistance
p-channel MOSFET bypass, IOUT = 400mA
VREFIN = 0.6V
77
mI
A
1.2
1.8
Step-Down Converter Current Limit in
Bypass Mode
1.3
1.6
Total Current Limit in Bypass Mode
2.5
3.4
Bypass LDO Current Limit
TA = +25NC
0.01
TA = +85NC
1
1.8
A
A
1
Bypass LDO Off-Leakage Current
VIN2 = 5.5V,
VOUT = 0V
Linear Bypass Regulation Threshold
Below nominal output voltage, IOUT = 0mA,
VREFIN = 0.5V or 1.2V
50
mV
Linear Bypass Regulation Enable
Threshold
Linear bypass is enabled when VOUT rises
above this threshold
1.0
V
25
mV
Linear Bypass Enable Threshold
Hysteresis
FA
STEP-DOWN CONVERTER
LX On-Resistance
LX Leakage Current
p-channel MOSFET, ILX = 100mA
0.175
0.300
n-channel MOSFET, ILX = 100mA
0.260
0.425
TA = +25NC
0.1
5
TA = +85NC
1
VEN = 0V, VLX = 0V
I
FA
p-Channel MOSFET Peak Current Limit
1.3
1.6
1.8
A
n-Channel MOSFET Valley Current Limit
1.0
1.3
1.5
A
n-Channel MOSFET Negative Current
Limit
1.2
1.5
1.8
A
Skip mode is disabled when VOUT rises above
this threshold
1.0
V
Automatic Skip Mode Enable Threshold
Hysteresis
25
mV
Static Zero-Crossing Threshold
20
mA
Minimum On- and Off-Times
70
Automatic Skip Mode Enable Threshold
No Load Switching Frequency
ns
TA = +25NC
1.74
2
2.35
TA = -40NC to +85NC
1.6
2
2.4
MHz
Note 3: The device is 100% production tested at TA = +25NC. Limits over the operating temperature range are guaranteed by design.
Maxim Integrated
3
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Typical Operating Characteristics
(Typical Operating Circuit, VIN1 = VIN2 = 3.7V, VREFIN = 0.9V, L1 = 4.7µH (TOKO DFE252012C), TA = +25NC, unless otherwise
noted.)
75
73
71
69
65
0
1000
FPWM
500
1000
1500
2000
2500
0
2000
1500
1000
FPWM
500
SKIP
0
0.4
MAX8989 toc03
2500
SKIP
0
0.8
1.2
1.6
0
2.0
0.4
0.8
1.2
1.6
2.0
REFIN VOLTAGE (V)
SWITCHING FREQUENCY vs. REFIN VOLTAGE
NO LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE (SKIP MODE)
NO LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE (FPWM MODE)
500
SKIP
0
0.8
1.2
1.6
TA = -40°C
TA = +25°C
60
VREFIN = 1.4V
-50
VREFIN = 0.2V
-100
VREFIN = 1.6V
-150
VREFIN = 0.4V
FORCED PWM
-200
500
1000
1500
LOAD CURRENT (mA)
2000
2500
1.5
0.5
0
3.1
3.5
3.9
4.3
4.7
LINE REGULATION ERROR
vs. SUPPLY VOLTAGE
VREFIN = 0.6V
2.0
0
2.7
100
500mA LOAD
50
0
5.1
5.5
DROPOUT
VREFIN = 0.4V
VREFIN = 1.6V
-150
2.7
3.1
3.5
3.9
4.3
4.7
SUPPLY VOLTAGE (V)
3.5
3.9
4.3
4.7
5.1
20
FORCED PWM
10
5.5
0
SKIP
-10
-20
DROPOUT
-30
NO LOAD
VIN = 3.7V
VREFIN = 1.4V
-200
2.7
3.1
OUTPUT VOLTAGE ERROR
vs. REFIN VOLTAGE
VREFIN = 0.6V
VREFIN = 0.8V
VREFIN = 1.0V
VREFIN = 1.2V
VREFIN = 0.2V
VREFIN = 0.2V
SUPPLY VOLTAGE (V)
-50
-100
VREFIN = 1.7V
2.5
20
LOAD REGULATION ERROR
vs. LOAD CURRENT
0
3.0
1.0
SUPPLY VOLTAGE (V)
50
3.5
40
2.0
ERROR = VOUT - 2VREFIN
0
100
REFIN VOLTAGE (V)
OUTPUT VOLTAGE ERROR (mV)
100
0.4
MAX8989 toc07
0
120
80
4.0
5.1
5.5
MAX8989 toc09
FPWM
TA = +85°C
140
TA = -40°C AND +85°C
4.5
SUPPLY CURRENT (µA)
1500
1000
160
5.0
OUTPUT VOLTAGE ERROR (mV)
2000
VREFIN < 0.5V
180
MAX8989 toc05
2500
200
SUPPLY CURRENT (µA)
VIN = 3.7V
40I LOAD
MAX8989 toc06
REFIN VOLTAGE (V)
MAX8989 toc04
SWITCHING FREQUENCY (kHz)
1500
VIN = 3.7V
10I LOAD
LOAD CURRENT (mA)
3000
OUTPUT VOLTAGE ERROR (mV)
2000
500
67
4 2500
3000
SWITCHING FREQUENCY (kHz)
77
VIN = 3.7V
4I LOAD
MAX8989 toc08
RESISTANCE (mI)
79
MAX8989 toc02
81
SWITCHING FREQUENCY vs. REFIN VOLTAGE
SWITCHING FREQUENCY vs. REFIN VOLTAGE
3000
SWITCHING FREQUENCY (kHz)
VIN = 3.4V
VREFIN = 2V
83
MAX8989 toc01
DROPOUT RESISTANCE vs. LOAD CURRENT
85
-40
0
0.4
0.8
1.2
REFIN VOLTAGE (V)
1.6
2.0
Maxim Integrated
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Typical Operating Characteristics (continued)
(Typical Operating Circuit, VIN1 = VIN2 = 3.7V, VREFIN = 0.9V, L1 = 4.7µH (TOKO DFE252012C), TA = +25NC, unless otherwise
noted.)
EFFICIENCY vs. OUTPUT VOLTAGE
VREFIN = 0.2V, SKIP = 0
0
VREFIN = 1.6V, SKIP = 0 OR 1
-10
-20
VREFIN = 0.2V, SKIP = 1
-45 -32 -19 -6
7
75
70
20 33 46 59 72 85
60
55
55
50
0.2 0.6 1.0 1.4 1.8 2.2 2.6 3.0 3.4 3.8 4.2
OUTPUT VOLTAGE (V)
MAX8989 toc13
VIN = 3.2V
80
VIN = 3.7V
90
VIN = 4.2V
75
70
VIN = 3.2V
95
85
100
VIN = 3.7V
VIN = 4.2V
95
80
75
70
85
70
65
60
60
55
55
50
50
80
VIN = 4.2V
75
VIN = 3.7V
70
100
LOAD CURRENT (mA)
Maxim Integrated
1000
VREFIN = 0.3V
20mA LOAD
VOUT
10mV/div
(AC-COUPLED)
50
SKIP = 0
60
30
10
LIGHT-LOAD SWITCHING WAVEFORMS (SKIP)
60
60
50
EFFICIENCY vs. LOAD CURRENT
70
40
VREFIN = 0.6V
1000
LOAD CURRENT (mA)
SKIP = 1
80
65
55
100
MAX8989 toc18
90
EFFICIENCY (%)
85
10
LOAD CURRENT (mA)
MAX8989 toc17
VIN = 3.2V
90
VREFIN = 0.9V
50
1000
100
MAX8989 toc16
95
55
VREFIN = 1.2V
EFFICIENCY vs. LOAD CURRENT
100
VIN = 3.7V
75
60
100
VIN = 4.2V
80
65
10
VIN = 3.2V
90
65
0.2 0.6 1.0 1.4 1.8 2.2 2.6 3.0 3.4 3.8 4.2
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
0.2 0.6 1.0 1.4 1.8 2.2 2.6 3.0 3.4 3.8 4.2
OUTPUT VOLTAGE (V)
EFFICIENCY vs. LOAD CURRENT
100
EFFICIENCY (%)
EFFICIENCY (%)
85
70
EFFICIENCY vs. LOAD CURRENT
10I LOAD
90
75
65
EFFICIENCY vs. OUTPUT VOLTAGE
95
VIN = 3.2V
80
60
50
VIN = 3.7V VIN = 4.2V
85
65
AMBIENT TEMPERATURE (°C)
100
MAX8989 toc11
VIN = 3.7V
MAX8989 toc14
NO LOAD
VIN = 3.7V
-15
VIN = 4.2V
80
90
EFFICIENCY (%)
-5
85
7.5I LOAD
95
MAX8989 toc15
EFFICIENCY (%)
OUTPUT VOLTAGE ERROR (mV)
90
10
5
VIN = 3.2V
5I LOAD
95
EFFICIENCY vs. OUTPUT VOLTAGE
100
EFFICIENCY (%)
NO LOAD
VIN = 3.7V
15
100
MAX8989 toc10
20
MAX8989 toc12
OUTPUT VOLTAGE ERROR
vs. TEMPERATURE
2V/div
VLX
VIN = 4.2V
VIN = 3.7V
20
VIN = 3.2V
VREFIN = 0.3V
10
0
10
100
IL
50mA/div
4µs/div
LOAD CURRENT (mA)
5
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Typical Operating Characteristics (continued)
(Typical Operating Circuit, VIN1 = VIN2 = 3.7V, VREFIN = 0.9V, L1 = 4.7µH (TOKO DFE252012C), TA = +25NC, unless otherwise
noted.)
LIGHT-LOAD SWITCHING
WAVEFORMS (FPWM)
MEDIUM-LOAD SWITCHING WAVEFORMS
MAX8989 toc20
MAX8989 toc19
VREFIN = 0.9V
500mA LOAD
VREFIN = 0.3V
20mA LOAD
10mV/div
(AC-COUPLED)
VOUT
2V/div
VLX
10mV/div
(AC-COUPLED)
VOUT
VLX
2V/div
200mA/div
IL
IL
50mA/div
400ns/div
400ns/div
HEAVY-LOAD SWITCHING WAVEFORMS
ENABLE WAVEFORMS
MAX8989 toc21
MAX8989 toc22
VREFIN = 1.6V
NO LOAD
VREFIN = 1.2V
2000mA LOAD
VOUT
10mV/div
(AC-COUPLED)
2V/div
EN
2V/div
VLX
2V/div
IL
VOUT
1A/div
IL
400ns/div
500mA/div
40µs/div
LINE TRANSIENT 4.2V TO 3.2V TO 4.2V
ENABLE WAVEFORMS
MAX8989 toc24
MAX8989 toc23
VREFIN = 1.6V
5I LOAD
VIN
VREFIN = 0.9V
36I LOAD
2V/div
EN
2V/div
VOUT
10mV/div
VOUT
IL
IL
50mA/div
500mA/div
40µs/div
6 1V/div
20µs/div
Maxim Integrated
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Typical Operating Characteristics (continued)
(Typical Operating Circuit, VIN1 = VIN2 = 3.7V, VREFIN = 0.9V, L1 = 4.7µH (TOKO DFE252012C), TA = +25NC, unless otherwise
noted.)
LOAD TRANSIENT 0mA TO 500mA (FPWM)
LOAD TRANSIENT 0mA TO 500mA (SKIP)
MAX8989 toc26
MAX8989 toc25
VREFIN = 0.4V
VOUT
IOUT
100mV/div
VOUT
200mA/div
IOUT
VREFIN = 0.4V
200mA/div
20µs/div
20µs/div
LOAD TRANSIENT 0mA TO 2500mA
REFIN TRANSIENT 0.2V TO 1.6V
MAX8989 toc27
VOUT
VREFIN = 1.6V
FPWM
MAX8989 toc28
5I LOAD
FPWM
VREFIN
100mV/div
1V/div
LDO TURN-ON
VOUT
IL
2V/div
1A/div
IL
0A
1A/div
1A/div
IOUT
10µs/div
10µs/div
REFIN TRANSIENT 0.6V TO 1.6V
REFIN TRANSIENT 0.2V TO 1.6V
MAX8989 toc29
IL
0A
VOUT
Maxim Integrated
VREFIN
2V/div
IL
0A
1A/div
10µs/div
NO LOAD
1V/div
1V/div
LDO TURN-ON
2V/div
MAX8989 toc31
NO LOAD
FPWM
1V/div VREFIN
VOUT
REFIN TRANSIENT 0.6V TO 1.6V
MAX8989 toc30
5I LOAD
VREFIN
100mV/div
VOUT
2V/div
0A
IL
1A/div
10µs/div
1A/div
10µs/div
7
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Typical Operating Characteristics
(Typical Operating Circuit, VIN1 = VIN2 = 3.7V, TA = +25°C, unless otherwise noted. PA operating characteristics based on
SKY77604 PA Module.)
GSM LOW-BAND PA VOLTAGE/CURRENT
vs. OUTPUT POWER
1000
90
800
1.5
600
1.0
400
0.5
200
70
0
65
1400
1200
1000
80
75
6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
OUTPUT POWER AT ANTENNA (dBm)
OUTPUT POWER AT ANTENNA (dBm)
GSM LOW-BAND BATTERY CURRENT
vs. OUTPUT POWER
GSM HIGH-BAND PA VOLTAGE/CURRENT
vs. OUTPUT POWER
MAX8989 toc34
3.0
ASSUMES 1.1dBm INSERTION LOSS
BETWEEN PA AND ANTENNA
2.5
GSM LB w/o DCDC
GSM LB w DC-DC
800
600
2.0
MAX8989 toc35
ASSUMES 1.8dBm INSERTION LOSS
BETWEEN PA AND ANTENNA
900
750
PA VOLTAGE
PA CURRENT
600
1.5
450
1.0
300
0.5
150
PA CURRENT (mA)
1600
6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
ASSUMES 1.1dBm INSERTION LOSS
BETWEEN PA AND ANTENNA
85
EFFICIENCY (%)
PA VOLTAGE
PA CURRENT
MAX8989 toc33
1200
2.0
0
400
200
0
0
6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
OUTPUT POWER AT ANTENNA (dBm)
GSM HIGH-BAND CONVERTER EFFICIENCY
vs. OUTPUT POWER
100
90
ASSUMES 1.8dBm INSERTION LOSS
BETWEEN PA AND ANTENNA
80
EFFICIENCY (%)
0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
OUTPUT POWER AT ANTENNA (dBm)
MAX8989 toc36
BATTERY CURRENT (mA)
95
PA VOLTAGE (V)
PA VOLTAGE (V)
2.5
1400
ASSUMES 1.1dBm INSERTION LOSS
BETWEEN PA AND ANTENNA
PA CURRENT (mA)
3.5
3.0
GSM LOW-BAND CONVERTER EFFICIENCY
vs. OUTPUT POWER
MAX8989 toc32
70
60
50
40
30
20
10
0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
OUTPUT POWER AT ANTENNA (dBm)
8 Maxim Integrated
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Typical Operating Characteristics (continued)
(Typical Operating Circuit, VIN1 = VIN2 = 3.7V, TA = +25°C, unless otherwise noted. PA operating characteristics based on
SKY77604 PA Module.)
GSM HIGH-BAND BATTERY CURRENT
vs. OUTPUT POWER
2.5
800
GSM HB w/o DCDC
GSM HB w DC-DC
400
200
0
0.5
75
80
12.5
10.0
70
7.5
60
5.0
50
2.5
40
3
9 15 21
-50 -30 -15 -9 -3
6 12 18 24
-40 -20 -12 -6 0
OUTPUT POWER AT ANTENNA (dBm)
Maxim Integrated
1000
15.0
0
BATTERY CURRENT (mA)
EFFICIENC Y (%)
90
ASSUMES
2dBm
INSERTION
LOSS
BETWEEN PA
AND ANTENNA
3
9 15 21
-50 -30 -15 -9 -3
6 12 18 24
-40 -20 -12 -6 0
OUTPUT POWER AT ANTENNA (dBm)
0
WCDMA BAND 5 BATTERY CURRENT
vs. OUTPUT POWER
DG09 (%)
MAX8989 toc39
EFFICIENCY
225
150
WCDMA BAND 5 PA CONVERTER
EFFICIENCY vs. OUTPUT POWER
DG09
PA VOLTAGE
1.0
OUTPUT POWER AT ANTENNA (dBm)
100
300
PA CURRENT
0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
375
2.0
1.5
450
100
MAX8989 toc40
ASSUMES 2dBm INSERTION LOSS BETWEEN
PA AND ANTENNA
15.0
WCDMA
w/o DCDC
12.5
WCDMA
w/ DC-DC
DG09
10.0
7.5
DG09 (%)
600
MAX8989 toc38
ASSUMES 2dBm INSERTION LOSS
BETWEEN PA AND ANTENNA
PA CURRENT (mA)
ASSUMES 1.8dBm INSERTION LOSS
BETWEEN PA AND ANTENNA
PA VOLTAGE (V)
BATTERY CURRENT (mA)
1000
3.0
MAX8989 toc37
1200
WCDMA BAND 5 PA VOLTAGE/CURRENT
vs. OUTPUT POWER
5.0
10
2.5
1
0
9 15 21
-50 -30 -15 -9 -3 3
-40 -20 -12 -6 0
6 12 18 24
OUTPUT POWER AT ANTENNA (dBm)
9
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Bump Configuration
TOP VIEW
BUMPS ON BOTTOM
MAX8989
+ AGND
REFIN
PGND
A1
A2
A3
EN
IN1
LX
B1
B2
B3
SKIP
IN2
OUT
C1
C2
C3
WLP
Bump Description
PIN
FUNCTION
AGND
Low-Noise Analog Ground. Connect AGND to the ground plane at a single point away from high
switching currents. See the PCB Layout section.
A2
REFIN
Reference Input. REFIN typically connects to the output of an external DAC used to control the IC’s
output voltage for continuous PA power adjustment. To improve noise immunity, bypass REFIN with a
1000pF capacitor to AGND. The output voltage regulates to 2.0 x VREFIN. REFIN is pulled down to ground
through an internal 800kI resistor.
A3
PGND
Power Ground. Connect PGND to the ground plane near the input and output capacitor grounds. See the
PCB Layout section.
B1
EN
Enable Input. Connect EN to IN_ or logic-high for normal operation. Connect EN to ground or logic-low to
shut down the output. EN is internally pulled down to ground through an 800kI resistor.
B2
IN1
Supply Voltage Input for the Step-Down Converter. Connect IN1 and IN2 to a battery or supply voltage
from 2.7V to 5.5V. Bypass IN1 with a 4.7FF ceramic capacitor as close as possible between IN1 and
PGND.
B3
LX
Inductor Connection
C1
SKIP
Skip Mode Enable Input. Connect SKIP to IN_ or logic-high to enable low-power skip mode during lightload operation when the output voltage is less than 1.0V. Connect SKIP to ground or logic-low for forced
PWM operation.
C2
IN2
Supply Voltage Input for the Bypass LDO. Connect IN1 and IN2 to a battery or supply voltage from 2.7V
to 5.5V. Bypass IN2 with a 4.7FF ceramic capacitor as close as possible between IN2 and PGND.
C3
OUT
Output of the Linear Bypass LDO. Connect OUT to the output of the step-down converter. Bypass OUT
with four 4.7FF ceramic capacitors as close as possible to OUT and PGND.
A1
10 NAME
Maxim Integrated
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
IN1
IN2
OUT
BYPASS LDO
C1
R3
BYPASS LDO
CONTROL
BIAS
AGND
REFIN
PWM ERROR
COMPARATOR
R4
C2
800kI
LX
STEP-DOWN
LOGIC
PGND
SKIP
STEP-DOWN
CURRENT LIMIT
R2
OUT EN
EN
CONTROL
LOGIC
R1
IN2
BANDGAP
MAX8989
800kI
Figure 1. Functional Diagram
tEN_BUCK
tBUCK_SS
VIN_
VEN
VOUT
Figure 2. Power-Up Timing
Maxim Integrated
11
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Detailed Description
The MAX8989 step-down converter is optimized for
powering the power amplifier (PA) in multistandard cellular handsets such as LTE, WCDMA, GSM, and EDGE.
The IC integrates a high-efficiency PWM step-down
converter for medium and low-power transmission with
an 85mI (typ) bypass regulator, in parallel with the
step-down converter, to power the PA during high-power
transmission.
Step-Down Converter
A hysteretic PWM control scheme ensures high efficiency, fast switching, fast transient response, low
output ripple, and physically tiny external components.
The control scheme is simple: when the output voltage
is below the regulation threshold, the error comparator
begins a switching cycle by turning on the high-side
switch. This high-side switch remains on until the minimum on-time expires and the output voltage is within
regulation, or the inductor current is above the currentlimit threshold. Once off, the high-side switch remains off
until the minimum off-time expires and the output voltage
falls again below the regulation threshold. During the off
period, the low-side synchronous rectifier turns on and
remains on until the high-side switch turns on again. The
internal synchronous rectifier eliminates the need for an
external Schottky diode.
Hysteretic control is sometimes referred to as ripple
control, since voltage ripple is used to control when the
high-side and low-side switches are turned on and off.
To ensure stability with low ESR ceramic output capacitors, the IC combines ripple from the output with the
ramp signal generated by the switching node (LX). This
is seen in Figure 1 with resistor R1 and capacitor C1 providing the combined ripple signal. Injecting ramp voltage
from the switching node also improves line regulation
because the slope of the ramp adjusts with changes in
input voltage.
Hysteretic control has a significant advantage over fixedfrequency control schemes: fast transient response.
Hysteretic control uses an error comparator, instead of
an error amplifier with compensation, and there is no
fixed-frequency clock. Therefore, a hysteretic converter
reacts virtually immediately to any load transient on the
output without having to wait for a new clock pulse or for
the output of the error amplifier to move as with a fixedfrequency converter.
12 With a fixed-frequency step-down converter, the magnitude of output voltage ripple is a function of the switching
frequency, inductor value, output capacitor and ESR,
and input and output voltage. Since the inductance value
and switching frequency are fixed, the output ripple varies with changes in line voltage. With a hysteretic stepdown converter, since the ripple voltage is essentially
fixed, the switching frequency varies with changes in
line voltage. Some variation with load current can also
be seen, however, this is part of what gives the hysteretic
converter its great transient response.
The IC is trimmed to provide a 2MHz switching frequency during 50% duty cycle condition (3.6V input and
1.8V output). See the Typical Operating Characteristics
section for more information on how switching frequency
can vary with respect to load current and supply voltage.
Voltage-Positioning Load Regulation
The IC step-down converter utilizes a unique feedback
network. By taking DC feedback from the LX node
through R1 of Figure 1, the usual phase lag due to the
output capacitor is removed, making the loop exceedingly stable and allowing the use of very small ceramic
output capacitors. To improve the load regulation, resistor R3 is included in the feedback. This configuration
yields load regulation equal to half of the inductor’s
series resistance multiplied by the load current. This
voltage-positioning load regulation greatly reduces overshoot during load transients and when changing the
output voltage from one level to another. However, when
calculating the required REFIN voltage, the load regulation should be considered. Because inductor resistance
(RL) is typically well specified and the typical PA is a
resistive load, the VREFIN to VOUT gain is slightly less
than 2.0V/V. The output voltage is approximately:
VOUT =2 × VREFIN -
1
× R L × ILOAD
2
When the output voltage drops by more than 60mV (typ)
due to load regulation (0.5 x RL x ILOAD > 60mV) and
the output voltage is above the linear bypass threshold
(1V typ), the linear bypass regulator starts to supplement
current to the output ensuring that the output is kept in
regulation. While the linear bypass regulator is sourcing
current, the step-down converter continues to supply
most of the load to maximize efficiency.
Maxim Integrated
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Skip Mode
The IC has an optional skip mode that provides the highest possible efficiency during light load conditions. Skip
mode is active when SKIP is logic-high and VOUT is less
than 1V.
In addition, when the bypass LDO is sourcing current,
skip mode is automatically enabled to prevent the stepdown converter from sinking current in an overvoltage
condition.
During skip mode, the hysteretic comparator turns on
the high-side switch based on the output voltage value.
Once the output voltage is high enough, the high-side
switch is turned off and the low-side switch is turned on
to return the inductor current to zero. A zero-crossing
comparator is enabled in this mode to minimize power
consumption by turning off the low-side switch as close
as possible to the true inductor-current zero-crossing. In
skip mode, the output ripple remains low at all loads, and
the switching frequency decreases with lighter loads.
Linear Bypass and Dropout
A low-dropout linear regulator is connected in parallel
with the step-down converter. The output voltage of the
linear regulator is set slightly lower than the nominal
regulation voltage of the step-down converter (60mV
typ). This allows the output to maintain regulation when
the output is slewed at a rate faster than the bandwidth
of the step-down converter and when the load current
exceeds the current limit of the step-down converter.
Linear bypass operation is disabled when the output
voltage is below the linear bypass regulation enable
threshold (1V typ).
The IC enters full dropout under two conditions:
U The IC is commanded to regulate to a setting higher
than VIN.
U REFIN is set to more than 2.1V (min).
Under either condition, the step-down converter goes to
100% duty cycle by turning on its p-channel MOSFET,
and the linear regulator enters dropout by turning on
fully. Note that forced dropout mode (the second condition) does not implement hysteresis on REFIN.
Shutdown
Connect EN to ground or logic-low to place the IC in
shutdown mode, reducing the input current to 0.1FA
(typ). In shutdown, the control circuitry, bypass linear
regulator, internal switching MOSFET, and synchronous
rectifier turn off, and LX becomes high impedance.
Connect EN to IN_ or logic-high for normal operation.
Maxim Integrated
Thermal Overload Protection
Thermal overload protection limits total power dissipation
in the IC. If the junction temperature exceeds +160NC,
the IC turns off, allowing it to cool. The IC turns on and
begins soft-start after the junction temperature cools by
20NC. This results in a pulsed output during continuous
thermal-overload conditions.
Applications Information
Inductor Selection
The step-down converter operates with a typical switching frequency of 2MHz. A 4.7FH is recommended for
best performance. The inductor’s DC current rating only
needs to match the maximum load of the application
because the IC features zero-current overshoot during
startup and load transients. See Table 1 for suggested
inductors and manufacturers.
Output Capacitor Selection
The output capacitor keeps the output voltage ripple
small and ensures regulation loop stability. COUT must
have low impedance at the switching frequency. Ceramic
capacitors with X5R or X7R temperature characteristics
are highly recommended due to their small size, low
ESR, and small temperature coefficients. Note that some
ceramic dielectrics exhibit large capacitance and ESR
variation with temperature and DC bias. Ceramic capacitors with Z5U or Y5V temperature characteristics should
be avoided. Tantalum capacitors are not recommended.
Four 4.7FF output capacitors are recommended for most
applications. For optimum load-transient performance
and very low output ripple, the output capacitor value
can be increased, however, care should be taken with
regards to output voltage slew rate requirements.
Input Capacitor Selection
The input capacitors reduce the current peaks drawn
from the battery or input power source and reduce
switching noise in the IC. The impedance of CIN1 and
CIN2 at the switching frequency should be kept very
low. Ceramic capacitors with X5R or X7R temperature
characteristics are highly recommended due to their
small size, low ESR, and small temperature coefficients.
Note that some ceramic dielectrics exhibit large capacitance and ESR variation with temperature and DC bias.
Ceramic capacitors with Z5U or Y5V temperature characteristics should be avoided.
For most applications, connect a 4.7FF capacitor from
IN1 to PGND and a 4.7FF capacitor from IN2 to PGND.
For optimum noise immunity and low input ripple, the
input capacitor value can be increased.
13
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Table 1. Suggested Inductors
MANUFACTURER
TOKO
TDK
Samsung
SERIES
INDUCTANCE
(µH)
RL
(mI typ)
CURRENT RATING
(mA)
DIMENSIONS
(mm max)
DEM2810C
4.7
170
1000
3.0 x 3.2 x 1.0
DFE252010C
4.7
320
1600
2.7 x 2.2 x 1.0
DFE252012C
4.7
210
1600
2.7 x 2.2 x 1.2
VLF302510
4.7
140
950
3.0 x 2.5 x 1.0
VLS252010T
4.7
367
980
2.6 x 2.1 x 1.0
CIG22H4R7MNE
4.7
233
1000
2.7 x 2.2 x 1.2
Thermal Considerations
In applications where the IC runs at high ambient temperatures or with heavy loads, the heat dissipated may
exceed the maximum junction temperature of the part. If
the junction temperature reaches approximately +160NC,
the thermal overload protection is activated.
The IC maximum power dissipation depends on the
thermal resistance of the package and circuit board,
the temperature difference between the die junction
and ambient air, and the rate of airflow. The maximum
allowed power dissipation is:
PMAX = (TJMAX - TA)/BJA
where TA is the ambient temperature, TJMAX is the
maximum junction temperature, and BJA is the junction to
ambient thermal resistance. See the Absolute Maximum
Ratings section.
The power dissipated in the device is approximately:
(
1 
PD =
VOUT × ILOAD x  - 1 - IL2 × R L
η 
)
Grounding of the IC is also critical. The AGND and
PGND must be routed as separate nets, and connected
together as close as possible to the PGND bump of the
IC. AGND can be used to shield REFIN along its routing.
AGND must be connected to the ground of the source
generating REFIN. To avoid noise coupling into AGND,
care must be taken in the layout to ensure isolation from
AGND to PGND, having cuts in the ground plane wherever necessary.
The input decoupling capacitor on IN1 filters the input
supply of the step-down converter. The layout needs
to ensure as short a path as possible from IN1, through
CIN1, to PGND for optimal decoupling. The point in the
layout where this input capacitor connects to PGND
serves as the star-connection ground point for all three
critical capacitors (CIN1, CIN2, and COUT).
The input decoupling capacitor on IN2 filters the input
supply for the linear regulator. Its bottom plate should be
routed to the star-ground point in the layout.
The OUT trace needs to be short and wide because it
carries the current from the linear regulator.
where E is the efficiency of the MAX8989 (see the Typical
Operating Characteristics section), ILOAD is the RMS
load current, IL is the RMS inductor current, and RL is
the inductor resistance.
The trace between the inductor and LX should also
be low impedance as this trace has a noisy, switching
waveform. Keep LX away from noise-sensitive traces
such as REFIN and AGND.
PCB Layout
The capacitor from REFIN to AGND is optional. The
REFIN capacitor can be used when needed to prevent
high-frequency noise from coupling into REFIN.
High switching frequencies and relatively large peak
currents make the PCB layout a very important part of
design. Good design minimizes excessive EMI on the
feedback paths and voltage gradients in the ground
plane, resulting in a stable and well-regulated output.
For the input supplies, it is critical to route them as separate lines from the power source with separate decoupling capacitors on IN1 and IN2. This is necessary to
prevent switching noise on IN1 from coupling into IN2.
14 The ground connection among CIN, COUT, and the PA
ground is also extremely critical. Parasitic impedance
in this ground connection results in degraded RF performance. Contact your Maxim representative for more
detailed information and assistance.
For a PCB layout example, refer to the MAX8989
Evaluation Kit data sheet.
Maxim Integrated
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Chip Information
PROCESS: BiCMOS
Maxim Integrated
Package Information
For the latest package outline information and land patterns, 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.
9 WLP
W91B1+1
21-0067
Refer to
Application
Note 1891
15
MAX8989
Multimode PA Step-Down Converter
with Linear Bypass Mode
Revision History
REVISION
NUMBER
REVISION
DATE
0
11/10
Initial release
—
1
1/11
Updated IN1, IN2, OUT, LX current absolute maximum rating
2
DESCRIPTION
PAGES
CHANGED
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.
16
© 2011
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
Maxim Integrated Products, Inc.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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