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.
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
Features
MAX1927/MAX1928
Ordering Information
PART
MAX1927REUB
PRESET
TEMP
PIN-
OUTPUT
PACKAGE
RANGE
VOLTAGE
Adj. to 0.75V -40°C to +85°C 10 µMAX
1.5V
1.8V
2.5V
-40°C to +85°C 10 µMAX
-40°C to +85°C 10 µMAX
-40°C to +85°C 10 µMAX
Applications
WCDMA Handsets
PDAs and Palmtops
DSP Core Power
Battery-Powered Equipment
MAX1928EUB15
MAX1928EUB18
MAX1928EUB25
Pin Configuration
TOP VIEW
PWM
1
GND
REF
FB
COMP
2
3
4
5
10
POK
9
BATT
V
IN
2.6V TO 5.5V
Typical Operating Circuit
PWM
L1
LX
SHDN
R
C
COMP
C
C
C
f
FB
C2
V
OUT
0.75V AT 800mA
BATT
C1
MAX1927R
MAX1928
8
LX
7
PGND
6
SHDN
MAX1927R
POK
µMAX
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.
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
MAX1927/MAX1928
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 (V
BATT
+ 0.3V)
Continuous Power Dissipation (T
A
= +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
(V
BATT
= 3.6V,
SHDN
= BATT, C
REF
= 0.1µF,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
BATT Input Voltage
Undervoltage Lockout Threshold
Quiescent Current
Quiescent Current in Dropout
Shutdown Supply Current
REFERENCE AND ERROR AMP
MAX1927R
FB Voltage Accuracy
MAX1928-15
MAX1928-18
MAX1928-25
FB Input Current
MAX1928
MAX1927R
MAX1927R
MAX1928-15
MAX1928-18
MAX1928-25
1.231
2.6V < V
BATT
< 5.5V
V
BATT
= 3.6V
V
BATT
= 2.6V
V
BATT
= 3.6V
V
BATT
= 2.6V
1.1
0.11
0.738
1.477
1.773
2.462
5
0.75
1.5
1.8
2.5
10
10
250
210
175
125
1.25
0.5
0.25
0.3
0.17
0.2
0.48
1.3
0.13
-0.55
1.6
0.15
0.762
1.523
1.827
2.538
15
150
µA
nA
V
SHDN
= GND
V
BATT
rising or falling (35mV hysteresis)
No load, pulse skipping, PWM = GND
1MHz switching
CONDITIONS
MIN
2.6
2.15
2.35
140
2
190
0.1
340
10
TYP
MAX
5.5
2.55
240
UNITS
V
V
µA
mA
µA
µA
Transconductance (g
m
)
µS
Reference Voltage Accuracy
Reference Supply Rejection
PWM CONTROLLER
P-Channel On-Resistance
N-Channel On-Resistance
Current-Sense Transresistance (R
CS
)
P-Channel Current-Limit Threshold
P-Channel Pulse-Skipping Current Threshold
N-Channel Negative Current-Limit Threshold
1.269
2
0.4
0.5
0.3
0.35
V
mV
Ω
Ω
V/A
A
A
A
2
_______________________________________________________________________________________
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
(V
BATT
= 3.6V,
SHDN
= BATT, C
REF
= 0.1µF,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +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
I
POK
= 0.1 mA
V
FB
= 0.5V, I
POK
= 1mA
V
POK
= 5.5V
MAX1927R
POK Threshold
MAX1928-15
MAX1928-18
MAX1928-25
Output Valid to POK Release Delay
LOGIC INPUTS (SHDN, PWM)
Logic Input High
Logic Input Low
Logic Input Current
2.6V < V
BATT
< 5.5 V
2.6V < V
BATT
< 5.5 V
V
BATT
= 5.5V
0.1
1.6
0.6
1
V
V
µA
POK transitions to high impedance 20ms
after V
FB
> V
POK
0.650
1.305
1.566
2.175
15
0.675
1.350
1.620
2.250
20
1
0.01
5.5
0.1
1
0.700
1.395
1.674
2.325
25
ms
V
V
V
µA
15°C hysteresis
PWM = GND
PWM = BATT
0.85
15
1
160
1.15
V
BATT
= 5.5V, LX = GND or BATT
-20
100
0
CONDITIONS
MIN
TYP
20
0.1
+20
MAX
UNITS
mA
µA
%
%
MHz
Degrees
MAX1927/MAX1928
ELECTRICAL CHARACTERISTICS
(V
BATT
= 3.6V,
SHDN
= BATT, C
REF
= 0.1µF,
T
A
= -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
MAX1927R
FB Voltage Accuracy
MAX1928-15
MAX1928-18
MAX1928-25
FB Input Current
MAX1928
0.732
1.47
1.764
2.45
5
0.768
1.53
1.836
2.55
15
µA
V
SHDN
= GND
V
BATT
rising or falling (35mV hysteresis)
No load, pulse skipping, PWM = GND
CONDITIONS
MIN
2.6
2.15
MAX
5.5
2.55
240
340
10
UNITS
V
V
µA
µA
µA
_______________________________________________________________________________________
3
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
MAX1927/MAX1928
ELECTRICAL CHARACTERISTICS (continued)
(V
BATT
= 3.6V,
SHDN
= BATT, C
REF
= 0.1µF,
T
A
= -40°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +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
I
POK
= 0.1 mA
V
FB
= 0.5V, I
POK
= 1mA
V
POK
= 5.5V
MAX1927R
MAX1928-15
POK Threshold
MAX1928-18
MAX1928-25
Output Valid to POK Release Delay
LOGIC INPUTS (SHDN, PWM)
Logic Input High
Logic Input Low
Logic Input Current
2.6V < V
BATT
< 5.5 V
2.6V < V
BATT
< 5.5 V
V
BATT
= 5.5V
1.6
0.6
1
V
V
µA
POK transitions to high impedance 20ms
after V
FB
> V
POK
0.650
1.305
1.566
2.175
15
PWM = GND
0.8
1
V
BATT
= 5.5V, LX = GND or BATT
2.6V < V
BATT
< 5.5V
V
BATT
= 3.6V
V
BATT
= 2.6V
V
BATT
= 3.6V
V
BATT
= 2.6V
1.1
0.10
-20
100
0
1.2
5.5
0.1
1
0.700
1.395
1.674
2.325
25
ms
V
0.10
MAX1927R
1.22
CONDITIONS
MIN
MAX
150
1.269
2
0.4
0.5
0.30
0.35
1.6
0.16
+20
UNITS
nA
V
mV
Ω
Ω
A
A
µA
%
%
MHz
V
V
µA
4
_______________________________________________________________________________________
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
MAX1927/MAX1928
Typical Operating Characteristics
(Circuits of Figure 3 and 4, T
A
= +25°C, unless otherwise noted.)
MAX1927R
EFFICIENCY vs. LOAD CURRENT
MAX1927 toc01
MAX1928-25
EFFICIENCY vs. LOAD CURRENT
MAX1927 toc02
MAX1928-18
EFFICIENCY vs. LOAD CURRENT
V
IN
= 2.7V
MAX1927 toc03
100
90
EFFICIENCY (%)
80
70
60
50
40
1
10
100
V
IN
= 5V
V
IN
= 3.6V
100
90
EFFICIENCY (%)
80
70
60
50
V
IN
= 5V
V
IN
= 3.6V
100
90
80
EFFICIENCY (%)
70
60
50
40
V
OUT
= 1.8V
30
V
IN
= 5V
V
IN
= 3.6V
V
OUT
= 3.3V
40
1000
1
10
100
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
1
10
100
1000
LOAD CURRENT (mA)
MAX1928-15
EFFICIENCY vs. LOAD CURRENT
V
IN
= 2.7V
90
80
EFFICIENCY (%)
70
60
50
40
V
OUT
= 1.5V
30
1
10
100
1000
LOAD CURRENT (mA)
30
1
V
IN
= 3.6V
V
IN
= 5V
MAX1927 toc04
MAX1927R
EFFICIENCY vs. LOAD CURRENT
MAX1927 toc05
MAX1928-25
DROPOUT VOLTAGE vs. LOAD CURRENT
450
DROPOUT VOLTAGE (mV)
400
350
300
250
200
150
100
MAX1927 toc06
100
100
90
80
EFFICIENCY (%)
70
60
50
40
V
OUT
= 1V
10
100
V
IN
= 3.6V
V
IN
= 5V
V
IN
= 2.7V
500
50
0
0
V
IN
= 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)
1000
LOAD CURRENT (mA)
MAX1928-18
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1927 toc07
NO-LOAD INPUT CURRENT
vs. INPUT VOLTAGE
MAX1927 toc08
OSCILLATOR FREQUENCY
vs. INPUT VOLTAGE
T
A
= +85°C
MAX1927 toc09
1.90
1.88
1.86
OUTPUT VOLTAGE (V)
1.84
1.82
1.80
1.78
1.76
1.74
1.72
1.70
V
IN
= 3.6V
400
350
INPUT CURRENT (µA)
300
250
200
150
100
50
0
1.06
OSCILLATOR FREQUENCY (MHz)
1.04
1.02
1.00
0.98
0.96
0.94
T
A
= -40°C
T
A
= +25°C
0 100 200 300 400 500 600 700 800 900 1000
LOAD CURRENT (mA)
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)
2.6
3.1
3.6
4.1
4.6
5.1
5.6
INPUT VOLTAGE (V)
_______________________________________________________________________________________
5
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