Low-Noise, 14V Input, 1A, PWM
Step-Down Converters
Typical Operating Characteristics (continued)
(Circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
LINE-TRANSIENT RESPONSE
MAX1684/85-19
MAX1684/MAX1685
START-UP CURRENT
MAX1684/85-20
V
IN
5V/div
0V
V
SHDN
5V/div
V
OUT
100mV/div
I
IN
50mA/div
2ms/div
MAX1684, I
LOAD
= 100mA, V
IN
= 5V TO 10V,
SYNC/PWM = 3.3V
10ms/div
MAX1684, I
LOAD
= 100mA, V
OUT
= 3.3V,
V
IN
= 5V, C
ILIM/SS
= 0.1µF, SYNC/PWM = 3.3V
Pin Description
PIN
1
2
3
4
5
6
7
8
NAME
CVH
AIN
IN
CVL
AGND
REF
FB
CC
FUNCTION
High-Side MOSFET Gate Bias. Bias voltage for P-channel switch. Bypass to IN with a 0.1µF capacitor.
Analog Supply Voltage Input. Connect to IN with a 0.2 in. metal trace. Bypass to PGND with a 0.1µF
capacitor.
Supply Voltage Input
Logic Supply Voltage Output and IC Logic Supply. Sources 5mA for external loads. Bypass to AGND
with 1µF capacitor.
Analog Ground
Reference Output. 1.25V reference output supplies 10µA for external loads. Bypass to AGND with 0.1µF
capacitor.
Dual Mode Feedback Input. Connect FB to V
OUT
for 1.25V output. Connect to an external resistor divider
to adjust the output voltage. Connect to AGND to set output voltage to 3.3V.
Integrator Capacitor Connection. Connect a 0.01µF capacitor to AGND.
SYNC/PWM Input:
For synchronized-PWM operation, drive with TTL level, 50% square wave.
Connect to CVL for PWM mode.
Connect to AGND for normal mode.
Current-Limit Adjust/Soft-Start Input. See
Current Limit and Soft-Start
section.
Standby Control Input. Connect to CVL for normal operation. Connect to AGND for low-power mode
(Table 1). This pin overrides SYNC/PWM setting.
Bootstrap Input. Connection for the bootstrap switch and internal feedback path. Connect BOOT to V
OUT
for V
OUT
< 5.5V. Connect BOOT to AGND for V
OUT
> 5.5V.
Inductor Connection. Drain for internal P-channel MOSFETs. Connect inductor from LX to OUT.
Active-Low Shutdown Input. Connect to ground for shutdown.
SHDN
can withstand the input voltage.
Power Ground
9
SYNC/PWM
10
11
12
13, 14
15
16
ILIM/SS
STBY
BOOT
LX
SHDN
PGND
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7
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
