Rainbow Electronics MAX1644 - Manual (Page 5)

MAX1644
2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
_______________________________________________________________________________________ 5
Typical Operating Characteristics (continued)
(Circuit of Figure 1, T A = +25°C, unless otherwise noted.)
NAME FUNCTION
1 SHDN
Shutdown Control Input. Drive SHDN low to disable the reference, control circuitry, and internal
MOSFETs. Drive high or connect to V
CC for normal operation.
PIN
Pin Description
V IN
V OUT
20mV/div
4V
3V
20 µs/div
LINE-TRANSIENT RESPONSE
MAX1644-10
V OUT = 1.5V, I OUT = 2A
I L
V
OUT
50mV/div
2A
0
20 µs/div
LOAD-TRANSIENT RESPONSE
(FBSEL = REF)
MAX1644-11
V IN = 3.3V, V OUT = 1.5V
2, 4 IN Supply Voltage Input for the internal PMOS power switch
3, 14, 16 LX
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.
5 SS Soft-Start. Connect a capacitor from SS to GND to limit inrush current during start-up.
6 COMP
Integrator Compensation. Connect a capacitor from COMP to V CC for integrator compensation. See the
Integrator Amplifier section.
7 TOFF
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 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 Analog Ground
10 REF Reference Output. Bypass REF to GND with a 1µF capacitor.
11 FBSEL
Feedback Select Input. Selects AC load-regulation error and output voltage. See Table 2 for program-
ming instructions.
12 V CC
Analog Supply Voltage Input. Supplies internal analog circuitry. Bypass V CC with a 10 Ω and 2.2µF low-
pass filter. See Figure 1.
13, 15 PGND Power Ground. Internally connected to the internal NMOS synchronous-rectifier switch.