3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converters
MAX756/MAX757
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
LOAD-TRANSIENT RESPONSE
START-UP DELAY
3V
OUTPUT
VOLTAGE
50mV/div
V
SHDN
2V/div
0V
5V
OUTPUT
CURRENT
0mA to 200mA
V
OUT
2V/div
0V
V
IN
= 2.5V
HORIZONTAL = 50µs/div
5V Mode
V
IN
= 2.5V
HORIZONTAL = 5ms/div
5V Mode
______________________________________________________________Pin Description
PIN
MAX756 MAX757
NAME
FUNCTION
Shutdown Input disables SMPS when low, but the voltage reference and low-battery com-
parator remain active.
Selects the main output voltage setting; 5V when low, 3.3V when high.
Feedback Input for adjustable output operation. Connect to an external voltage divider
between OUT and GND.
1.25V Reference Voltage Output. Bypass with 0.22µF to GND (0.1µF if there is no external
reference load). Maximum load capability is 250µA source, 20µA sink.
Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at
LBI drops below +1.25V.
Low-Battery Input. When the voltage on LBI drops below +1.25V, LBO sinks current.
Connect to V
IN
if not used.
Connect OUT to the regulator output. It provides bootstrapped power to both devices,
and also senses the output voltage for the MAX756.
Power Ground. Must be low impedance; solder directly to ground plane.
1A, 0.5Ω N-Channel Power MOSFET Drain
1
2
–
1
–
2
SHDN
3/5
FB
3
3
REF
4
4
LBO
5
5
LBI
6
7
8
4
6
7
8
OUT
GND
LX
_______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
