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Part Number MAX1927R

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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
MAX1927/MAX1928
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
________________________________________________________________ Maxim Integrated Products
1
Ordering Information
BATT
COMP
GND
REF
PGND
LX
POK
FB
V
IN
2.6V TO 5.5V
C1
C2
C
C
R
C
L1
V
OUT
0.75V AT 800mA
SHDN
PWM
MAX1927R
C
f
Typical Operating Circuit
19-2527; Rev 0; 7/02
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.
PART
PRESET
OUTPUT
VOLTAGE
TEMP
RANGE
PIN-
PACKAGE
MAX1927REUB
Adj. to 0.75V -40
°C to +85°C 10 µMAX
MAX1928EUB15
1.5V
-40
°C to +85°C 10 µMAX
MAX1928EUB18
1.8V
-40
°C to +85°C 10 µMAX
MAX1928EUB25
2.5V
-40
°C to +85°C 10 µMAX
1
2
3
4
5
10
9
8
7
6
POK
BATT
LX
PGND
FB
REF
GND
PWM
MAX1927R
MAX1928
µMAX
TOP VIEW
COMP
SHDN
Pin Configuration
MAX1927/MAX1928
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.)
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.
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
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
BATT Input Voltage
2.6
5.5
V
Undervoltage Lockout Threshold
V
BATT
rising or falling (35mV hysteresis)
2.15
2.35
2.55
V
No load, pulse skipping, PWM = GND
140
240
µA
Quiescent Current
1MHz switching
2
mA
Quiescent Current in Dropout
190
340
µA
Shutdown Supply Current
SHDN = GND
0.1
10
µA
REFERENCE AND ERROR AMP
MAX1927R
0.738
0.75
0.762
MAX1928-15
1.477
1.5
1.523
MAX1928-18
1.773
1.8
1.827
FB Voltage Accuracy
MAX1928-25
2.462
2.5
2.538
V
MAX1928
5
10
15
µA
FB Input Current
MAX1927R
10
150
nA
MAX1927R
250
MAX1928-15
210
MAX1928-18
175
Transconductance (g
m
)
MAX1928-25
125
µS
Reference Voltage Accuracy
1.231
1.25
1.269
V
Reference Supply Rejection
2.6V < V
BATT
< 5.5V
0.5
2
mV
PWM CONTROLLER
V
BATT
= 3.6V
0.25
0.4
P-Channel On-Resistance
V
BATT
= 2.6V
0.3
0.5
V
BATT
= 3.6V
0.17
0.3
N-Channel On-Resistance
V
BATT
= 2.6V
0.2
0.35
Current-Sense Transresistance (R
CS
)
0.48
V/A
P-Channel Current-Limit Threshold
1.1
1.3
1.6
A
P-Channel Pulse-Skipping Current Threshold
0.11
0.13
0.15
A
N-Channel Negative Current-Limit Threshold
-0.55
A
MAX1927/MAX1928
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
_______________________________________________________________________________________
3
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
CONDITIONS
MIN
TYP
MAX
UNITS
N-Channel Synchronous Rectifier Turn-Off
Threshold
20
mA
LX Leakage Current
V
BATT
= 5.5V, LX = GND or BATT
-20
0.1
+20
µA
Maximum Duty Cycle
100
%
PWM = GND
0
Minimum Duty Cycle
PWM = BATT
15
%
Internal Oscillator Frequency
0.85
1
1.15
MHz
Thermal Shutdown Threshold
15°C hysteresis
160
D eg r ees
POK COMPARATOR
BATT Operating Voltage Range
I
POK
= 0.1 mA
1
5.5
V
Output Low Voltage
V
FB
= 0.5V, I
POK
= 1mA
0.01
0.1
V
Output High Leakage Current
V
POK
= 5.5V
1
µA
MAX1927R
0.650
0.675
0.700
MAX1928-15
1.305
1.350
1.395
MAX1928-18
1.566
1.620
1.674
POK Threshold
MAX1928-25
2.175
2.250
2.325
V
Output Valid to POK Release Delay
POK transitions to high impedance 20ms
after V
FB
> V
POK
15
20
25
ms
LOGIC INPUTS (SHDN, PWM)
Logic Input High
2.6V < V
BATT
< 5.5 V
1.6
V
Logic Input Low
2.6V < V
BATT
< 5.5 V
0.6
V
Logic Input Current
V
BATT
= 5.5V
0.1
1
µA
ELECTRICAL CHARACTERISTICS
(V
BATT
= 3.6V, SHDN = BATT, C
REF
= 0.1µF, T
A
= -40°C to +85°C, unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
MAX
UNITS
BATT Input Voltage
2.6
5.5
V
Undervoltage Lockout Threshold
V
BATT
rising or falling (35mV hysteresis)
2.15
2.55
V
Quiescent Current
No load, pulse skipping, PWM = GND
240
µA
Quiescent Current in Dropout
340
µA
Shutdown Supply Current
SHDN = GND
10
µA
REFERENCE AND ERROR AMP
MAX1927R
0.732
0.768
MAX1928-15
1.47
1.53
MAX1928-18
1.764
1.836
FB Voltage Accuracy
MAX1928-25
2.45
2.55
V
FB Input Current
MAX1928
5
15
µA
MAX1927/MAX1928
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
4
_______________________________________________________________________________________
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
CONDITIONS
MIN
MAX
UNITS
FB Input Current
MAX1927R
150
nA
Reference Voltage Accuracy
1.22
1.269
V
Reference-Supply Rejection
2.6V < V
BATT
< 5.5V
2
mV
PWM CONTROLLER
V
BATT
= 3.6V
0.4
P-Channel On-Resistance
V
BATT
= 2.6V
0.5
V
BATT
= 3.6V
0.30
N-Channel On-Resistance
V
BATT
= 2.6V
0.35
P-Channel Current-Limit Threshold
1.1
0.10
1.6
A
P-Channel Pulse-Skipping Current Threshold
0.10
0.16
A
LX Leakage Current
V
BATT
= 5.5V, LX = GND or BATT
-20
+20
µA
Maximum Duty Cycle
100
%
Minimum Duty Cycle
PWM = GND
0
%
Internal Oscillator Frequency
0.8
1.2
MHz
POK COMPARATOR
BATT Operating Voltage Range
I
POK
= 0.1 mA
1
5.5
V
Output Low Voltage
V
FB
= 0.5V, I
POK
= 1mA
0.1
V
Output High Leakage Current
V
POK
= 5.5V
1
µA
MAX1927R
0.650
0.700
MAX1928-15
1.305
1.395
MAX1928-18
1.566
1.674
POK Threshold
MAX1928-25
2.175
2.325
V
Output Valid to POK Release Delay
POK transitions to high impedance 20ms
after V
FB
> V
POK
15
25
ms
LOGIC INPUTS (SHDN, PWM)
Logic Input High
2.6V < V
BATT
< 5.5 V
1.6
V
Logic Input Low
2.6V < V
BATT
< 5.5 V
0.6
V
Logic Input Current
V
BATT
= 5.5V
1
µA
MAX1927/MAX1928
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
_______________________________________________________________________________________
5
MAX1927 toc01
LOAD CURRENT (mA)
EFFICIENCY (%)
100
10
50
60
70
80
90
100
40
1
1000
MAX1927R
EFFICIENCY vs. LOAD CURRENT
V
IN
= 5V
V
IN
= 3.6V
V
OUT
= 3.3V
MAX1928-25
EFFICIENCY vs. LOAD CURRENT
MAX1927 toc02
LOAD CURRENT (mA)
EFFICIENCY (%)
100
10
50
60
70
80
90
100
40
1
1000
V
IN
= 5V
V
IN
= 3.6V
MAX1928-18
EFFICIENCY vs. LOAD CURRENT
MAX1927 toc03
LOAD CURRENT (mA)
EFFICIENCY (%)
100
10
40
50
60
70
80
90
100
30
1
1000
V
IN
= 5V
V
IN
= 2.7V
V
IN
= 3.6V
V
OUT
= 1.8V
MAX1928-15
EFFICIENCY vs. LOAD CURRENT
MAX1927 toc04
LOAD CURRENT (mA)
EFFICIENCY (%)
100
10
40
50
60
70
80
90
100
30
1
1000
V
OUT
= 1.5V
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 5V
MAX1927R
EFFICIENCY vs. LOAD CURRENT
MAX1927 toc05
LOAD CURRENT (mA)
EFFICIENCY (%)
100
10
40
50
60
70
80
90
100
30
1
1000
V
OUT
= 1V
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 5V
MAX1928-25
DROPOUT VOLTAGE vs. LOAD CURRENT
MAX1927 toc06
LOAD CURRENT (A)
DROPOUT VOLTAGE (mV)
0.9
0.8
0.6 0.7
0.2 0.3 0.4 0.5
0.1
50
100
150
200
250
300
350
400
450
500
0
0
1.0
V
IN
= 2.5V
MAX1928-18
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1927 toc07
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
900
800
600 700
200 300 400 500
100
1.72
1.74
1.76
1.78
1.80
1.82
1.84
1.86
1.88
1.90
1.70
0
1000
V
IN
= 3.6V
MAX1927 toc08
INPUT VOLTAGE (V)
INPUT CURRENT (
µ
A)
5.0
4.5
0.5 1.0 1.5
2.5 3.0 3.5
2.0
4.0
50
100
150
200
250
300
350
400
0
0
5.5
NO-LOAD INPUT CURRENT
vs. INPUT VOLTAGE
OSCILLATOR FREQUENCY
vs. INPUT VOLTAGE
MAX1927 toc09
INPUT VOLTAGE (V)
OSCILLATOR FREQUENCY (MHz)
5.1
4.6
4.1
3.6
3.1
0.96
0.98
1.00
1.02
1.04
1.06
0.94
2.6
5.6
T
A
= +85
°C
T
A
= +25
°C
T
A
= -40
°C
Typical Operating Characteristics
(Circuits of Figure 3 and 4, T
A
= +25°C, unless otherwise noted.)