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19-2527; Rev 0; 7/02
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
General Description
The MAX1927/MAX1928 800mA step-down converters
power low-voltage microprocessors in compact equip-
ment requiring the highest possible efficiency. The
MAX1927/MAX1928 are optimized for generating low
output voltages (down to 750mV) at high efficiency
using small external components. The supply voltage
range is from 2.6V to 5.5V and the guaranteed minimum
output current is 800mA. 1MHz pulse-width modulation
(PWM) switching allows for small external components.
A unique control scheme minimizes ripple at light loads,
while maintaining a low 140µA quiescent current.
The MAX1927/MAX1928 include a low on-resistance
internal MOSFET switch and synchronous rectifier to
maximize efficiency and minimize external component
count. No external diode is needed. 100% duty-cycle
operation allows for a dropout voltage of only 340mV at
800mA. Other features include internal soft-start,
power-OK (POK) output, and selectable forced PWM
operation for lower noise at all load currents.
The MAX1928 is available with several preset output
voltages: 1.5V (MAX1928-15), 1.8V (MAX1928-18), and
2.5V (MAX1928-25). The MAX1927R has adjustable
output range down to 0.75V. The MAX1927/MAX1928
are available in a tiny 10-pin µMAX package.
Applications
WCDMA Handsets
PDAs and Palmtops
DSP Core Power
Battery-Powered Equipment
Features
o 800mA Output Current
o Output Voltages from 0.75V to 5V
o 2.6V to 5.5V Input Voltage Range
o Power-OK Output
o No Schottky Diode Required
o Selectable Forced PWM Operation
o 1MHz Fixed-Frequency PWM Operation
o 140µA Quiescent Current
o Soft-Start
o 10-Pin µMAX Package
Ordering Information
PART
MAX1927REUB
MAX1928EUB15
MAX1928EUB18
MAX1928EUB25
PRESET
OUTPUT
VOLTAGE
TEMP
RANGE
PIN-
PACKAGE
Adj. to 0.75V -40°C to +85°C 10 µMAX
1.5V
-40°C to +85°C 10 µMAX
1.8V
-40°C to +85°C 10 µMAX
2.5V
-40°C to +85°C 10 µMAX
Pin Configuration
TOP VIEW
PWM 1
GND 2
REF 3
FB 4
COMP 5
MAX1927R
MAX1928
10 POK
9 BATT
8 LX
7 PGND
6 SHDN
µMAX
Typical Operating Circuit
VIN
2.6V TO 5.5V
C1
BATT
PWM
LX
SHDN
FB
RC MAX1927R
COMP
POK
CC Cf
L1
VOUT
0.75V AT 800mA
C2
REF PGND
GND
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

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Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
ABSOLUTE MAXIMUM RATINGS
BATT, PWM, POK, COMP, SHDN to GND ...............-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
LX, REF, FB to GND ................................-0.3V to (VBATT + 0.3V)
Continuous Power Dissipation (TA = +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW
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
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
(VBATT = 3.6V, SHDN = BATT, CREF = 0.1µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
BATT Input Voltage
Undervoltage Lockout Threshold
Quiescent Current
Quiescent Current in Dropout
Shutdown Supply Current
REFERENCE AND ERROR AMP
FB Voltage Accuracy
FB Input Current
Transconductance (gm)
Reference Voltage Accuracy
Reference Supply Rejection
PWM CONTROLLER
P-Channel On-Resistance
N-Channel On-Resistance
Current-Sense Transresistance (RCS )
P-Channel Current-Limit Threshold
P-Channel Pulse-Skipping Current Threshold
N-Channel Negative Current-Limit Threshold
CONDITIONS
VBATT rising or falling (35mV hysteresis)
No load, pulse skipping, PWM = GND
1MHz switching
SHDN = GND
MAX1927R
MAX1928-15
MAX1928-18
MAX1928-25
MAX1928
MAX1927R
MAX1927R
MAX1928-15
MAX1928-18
MAX1928-25
2.6V < VBATT < 5.5V
VBATT = 3.6V
VBATT = 2.6V
VBATT = 3.6V
VBATT = 2.6V
MIN
2.6
2.15
TYP
2.35
140
2
190
0.1
MAX
5.5
2.55
240
340
10
UNITS
V
V
µA
mA
µA
µA
0.738 0.75 0.762
1.477 1.5 1.523
1.773 1.8 1.827
2.462 2.5 2.538
5 10 15
10 150
250
210
175
125
1.231 1.25 1.269
0.5 2
V
µA
nA
µS
V
mV
1.1
0.11
0.25
0.3
0.17
0.2
0.48
1.3
0.13
-0.55
0.4
0.5
0.3
0.35
1.6
0.15
V/A
A
A
A
2 _______________________________________________________________________________________

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Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
(VBATT = 3.6V, SHDN = BATT, CREF = 0.1µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
N-Channel Synchronous Rectifier Turn-Off
Threshold
LX Leakage Current
Maximum Duty Cycle
Minimum Duty Cycle
Internal Oscillator Frequency
Thermal Shutdown Threshold
POK COMPARATOR
BATT Operating Voltage Range
Output Low Voltage
Output High Leakage Current
POK Threshold
Output Valid to POK Release Delay
LOGIC INPUTS (SHDN, PWM)
Logic Input High
Logic Input Low
Logic Input Current
CONDITIONS
VBATT = 5.5V, LX = GND or BATT
PWM = GND
PWM = BATT
15°C hysteresis
IPOK = 0.1 mA
VFB = 0.5V, IPOK = 1mA
VPOK = 5.5V
MAX1927R
MAX1928-15
MAX1928-18
MAX1928-25
POK transitions to high impedance 20ms
after VFB > VPOK
2.6V < VBATT < 5.5 V
2.6V < VBATT < 5.5 V
VBATT = 5.5V
MIN
-20
100
0.85
TYP
20
0.1
15
1
160
MAX UNITS
mA
+20 µA
%
0
%
1.15 MHz
Degrees
1
0.650
1.305
1.566
2.175
0.01
0.675
1.350
1.620
2.250
5.5
0.1
1
0.700
1.395
1.674
2.325
15 20 25
V
V
µA
V
ms
1.6
0.6
0.1 1
V
V
µA
ELECTRICAL CHARACTERISTICS
(VBATT = 3.6V, SHDN = BATT, CREF = 0.1µF, TA = -40°C to +85°C, unless otherwise noted.)
PARAMETER
BATT Input Voltage
Undervoltage Lockout Threshold
Quiescent Current
Quiescent Current in Dropout
Shutdown Supply Current
REFERENCE AND ERROR AMP
FB Voltage Accuracy
FB Input Current
CONDITIONS
VBATT rising or falling (35mV hysteresis)
No load, pulse skipping, PWM = GND
SHDN = GND
MAX1927R
MAX1928-15
MAX1928-18
MAX1928-25
MAX1928
MIN
2.6
2.15
0.732
1.47
1.764
2.45
5
MAX
5.5
2.55
240
340
10
UNITS
V
V
µA
µA
µA
0.768
1.53
1.836
2.55
15
V
µA
_______________________________________________________________________________________ 3

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Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
(VBATT = 3.6V, SHDN = BATT, CREF = 0.1µF, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
FB Input Current
Reference Voltage Accuracy
Reference-Supply Rejection
PWM CONTROLLER
P-Channel On-Resistance
N-Channel On-Resistance
P-Channel Current-Limit Threshold
P-Channel Pulse-Skipping Current Threshold
LX Leakage Current
Maximum Duty Cycle
Minimum Duty Cycle
Internal Oscillator Frequency
POK COMPARATOR
BATT Operating Voltage Range
Output Low Voltage
Output High Leakage Current
POK Threshold
Output Valid to POK Release Delay
LOGIC INPUTS (SHDN, PWM)
Logic Input High
Logic Input Low
Logic Input Current
MAX1927R
CONDITIONS
2.6V < VBATT < 5.5V
VBATT = 3.6V
VBATT = 2.6V
VBATT = 3.6V
VBATT = 2.6V
VBATT = 5.5V, LX = GND or BATT
PWM = GND
IPOK = 0.1 mA
VFB = 0.5V, IPOK = 1mA
VPOK = 5.5V
MAX1927R
MAX1928-15
MAX1928-18
MAX1928-25
POK transitions to high impedance 20ms
after VFB > VPOK
2.6V < VBATT < 5.5 V
2.6V < VBATT < 5.5 V
VBATT = 5.5V
MIN
1.22
MAX
150
1.269
2
UNITS
nA
V
mV
1.1
0.10
-20
100
0.8
0.10
0.4
0.5
0.30
0.35
1.6
0.16
+20
0
1.2
A
A
µA
%
%
MHz
1
0.650
1.305
1.566
2.175
15
5.5
0.1
1
0.700
1.395
1.674
2.325
25
V
V
µA
V
ms
1.6 V
0.6 V
1 µA
4 _______________________________________________________________________________________

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Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
(Circuits of Figure 3 and 4, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics
MAX1927R
EFFICIENCY vs. LOAD CURRENT
100
VIN = 3.6V
90
80
70 VIN = 5V
60
50
40
1
VOUT = 3.3V
10 100
LOAD CURRENT (mA)
1000
MAX1928-15
EFFICIENCY vs. LOAD CURRENT
100
VIN = 2.7V
90
80
70 VIN = 5V
60 VIN = 3.6V
50
40
30
1
VOUT = 1.5V
10 100
LOAD CURRENT (mA)
1000
MAX1928-18
OUTPUT VOLTAGE vs. LOAD CURRENT
1.90
1.88
1.86
1.84
1.82
1.80
1.78
1.76
1.74
1.72 VIN = 3.6V
1.70
0 100 200 300 400 500 600 700 800 900 1000
LOAD CURRENT (mA)
MAX1928-25
EFFICIENCY vs. LOAD CURRENT
100
90 VIN = 3.6V
80
70 VIN = 5V
60
50
40
1
10 100
LOAD CURRENT (mA)
1000
MAX1927R
EFFICIENCY vs. LOAD CURRENT
100
90 VIN = 2.7V
80
70 VIN = 5V
60 VIN = 3.6V
50
40
30
1
VOUT = 1V
10 100
LOAD CURRENT (mA)
1000
NO-LOAD INPUT CURRENT
vs. INPUT VOLTAGE
400
350
300
250
200
150
100
50
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
MAX1928-18
EFFICIENCY vs. LOAD CURRENT
100
90 VIN = 2.7V
80 VIN = 3.6V
70
60 VIN = 5V
50
40
30
1
VOUT = 1.8V
10 100
LOAD CURRENT (mA)
1000
MAX1928-25
DROPOUT VOLTAGE vs. LOAD CURRENT
500
450
400
350
300
250
200
150
100
50
0
0
VIN = 2.5V
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
LOAD CURRENT (A)
OSCILLATOR FREQUENCY
vs. INPUT VOLTAGE
1.06
TA = +85°C
1.04
1.02
1.00 TA = +25°C
0.98
0.96 TA = -40°C
0.94
2.6 3.1 3.6 4.1 4.6 5.1 5.6
INPUT VOLTAGE (V)
_______________________________________________________________________________________ 5