2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
Typical Operating Characteristics (continued)
(Circuit of Figure 1, T = +25°C, unless otherwise noted.)
A
LOAD-TRANSIENT RESPONSE
(FBSEL = REF)
LINE-TRANSIENT RESPONSE
4V
IN
2A
V
I
3V
L
0
V
= 1.5V, I
= 2A
V
= 3.3V, V
= 1.5V
OUT
OUT
IN
OUT
V
OUT
50mV/div
V
OUT
20mV/div
20μs/div
20μs/div
Pin Description
PIN
NꢀME
FUNCTI N
Shutdown Control Input. Drive SHDN low to disable the reference, control circuitry, and internal
MOSFETs. Drive high or connect to V for normal operation.
1
SHDN
IN
CC
2, 4
Supply Voltage Input for the internal PMOS power switch
Connection for the drains of the PMOS power switch and NMOS synchronous-rectifier switch. Connect
the inductor from this node to output filter capacitor and load.
3, 14, 16
LX
5
6
SS
Soft-Start. Connect a capacitor from SS to GND to limit inrush current during start-up.
Integrator Compensation. Connect a capacitor from COMP to V
for integrator compensation. See the
CC
COMP
Integrator Amplifier section.
Off-Time Select Input. Sets the PMOS power switch off-time during constant-off-time operation. Connect a
resistor from TOFF to GND to adjust the PMOS switch off-time.
ꢀ
8
TOFF
FB
Feedback Input for both preset-output and adjustable-output operating modes. Connect directly to
output for fixed-voltage operation or to a resistor-divider for adjustable operating modes.
9
GND
REF
Analog Ground
10
Reference Output. Bypass REF to GND with a 1µF capacitor.
Feedback Select Input. Selects AC load-regulation error and output voltage. See Table 2 for program-
ming instructions.
11
FBSEL
Analog Supply Voltage Input. Supplies internal analog circuitry. Bypass V
pass filter. See Figure 1.
with a 10Ω and 2.2µF low-
CC
12
V
CC
13, 15
PGND
Power Ground. Internally connected to the internal NMOS synchronous-rectifier switch.
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5
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
