Rainbow Electronics MAX1842 - Manual (Page 8)

MAX1742/MAX1842
1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
8 _______________________________________________________________________________________
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
MAX1842
LOAD-TRANSIENT RESPONSE
V
OUTPUT
50mV/div
I L
2A/div
MAX1842 toc17
10 µs/div
0
MAX1842
LINE-TRANSIENT RESPONSE
V INPUT
2V/div
V OUTPUT
20mV/div
AC-COUPLED
MAX1842 toc18
20 µs/div
I OUT = 2.5A, V OUT = 1.5V, R TOFF = 100k Ω, L = 2.2 µ H
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 the output filter capacitor and load.
5 SS Soft-Start. Connect a capacitor from SS to GND to limit inrush current during startup.
6 COMP
Integrator Compensation. Connect a capacitor from COMP to V CC for integrator compensation. See
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 resistive 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 output voltage. See Table 3 for programming 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.
Typical Operating Characteristics (continued)
(Circuit of Figure 1, T A = +25°C, unless otherwise noted.)