High-Efficiency Step-Up
Current Regulator for LEDs
Pin Description
PIN NAME
FUNCTION
1
VCC
IC Supply Voltage Input. Power for internal circuitry. Input range is 2.7V to 5.5V.
Active-Low Shutdown Input. In shutdown, the MOSFET turns off, but a current path still exists between the
2
SHDN input and output. The minimum forward voltage of the LED array must exceed the maximum VBATT to ensure
that the LEDs are off in shutdown.
3
REF
1.25V Reference Output. Capable of sourcing 150µA for external loads. This pin is internally compensated.
Do not connect any bypass capacitors at REF.
4
ADJ
Adjust Input. Allows dynamic adjustment of the output current. FB regulates to 300mV when ADJ = REF.
5, 7
GND Ground
6
FB
Feedback Input. Connect to the external LED current-sense feedback resistor.
8
PGND Power Ground
9
CS
FET Current-Sense Input
10
EXT
Gate Driver Output
SHDN
VCC
ADJ
MAX1698
UNDERVOLTAGE
LOCKOUT/
SHUTDOWN
FB
GND
TRIG
MAX tON
Q
TRIG
MIN tOFF
Q
SOFT-START
CS
VCC
EXT
PGND
1.25V
REFERENCE
REF
Figure 1. Functional Diagram
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