Datasheet

MAX1927/MAX1928
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
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Pin Description
PIN
NAME
FUNCTION
1
PWM
Forced-PWM Input. Drive to GND to use PWM at medium to heavy loads and pulse-skipping at light loads.
Drive to BATT to force PWM operation at all loads.
2 GND Ground
3 REF Internal 1.25V Reference. Bypass to GND with a 0.1µF capacitor.
4FB
Output Feedback Sense Input. To set the output voltage to the preset voltage (MAX1928), connect FB directly
to the output. To adjust the output voltage (MAX1927R), connect FB to the center of an external resistor-
divider between the output and GND. FB regulation voltage is 0.75V.
5
COMP
Compensation Input. See the Compensation, Stability, and Output Capacitor section for compensation
component selection.
6
SHDN
Shutdown Control Input. Drive low to shut down the converter. Drive high for normal operation.
7
PGND
Power Ground
8 LX Inductor Connection to the drains of the internal power MOSFETs.
9
BATT
Supply Voltage Input. Connect to a 2.6V to 5.5V source. Bypass to GND with a low-ESR 10µF capacitor.
10 POK
Power-OK Open-Drain Output. Once the soft-start routine has completed, POK goes high impedance 20ms
after FB exceeds 90% of its expected final value.
N
N
P
P
SLOPE
COMPENSATION
POWER-OK
CONTROL
1MHz
OSC
BIAS
COMP
BATT
PWM
CONTROL
1.25V
REFERENCE
PFM CURRENT
COMPARATOR
PWM
COMPARATOR
PWM
ILIM
COMPARATOR
TO
COMP
N-CHANNEL
CURRENT COMPARATOR
PGND
POK
FB
REF
MAX1927R
ONLY
GND
MAX1928
ONLY
LX
SHDN
MAX1927
MAX1928
Figure 1. Simplified Functional Diagram