HT7937
Built-in OVP White LED Step-up Converter
Features
·
Integrated open-circuit protection
·
Over voltage protection
·
Up to 84% efficiency at V
IN
=3V, 3LEDs,
·
Low standby current: 0.1mA (typ.) (V
SHDN
=0V)
·
Matches LED current
·
Small value inductor and capacitors
·
Small outline SOT23-6 package
I
LED
= 20mA
·
1.2MHz fixed switching frequency
Applications
·
Cellular phones
·
PDAs
·
DSCs
·
Handheld devices
·
White LED display backlighting
General Description
The HT7937 is high efficiency boost converter with a
constant current output to provide back light functions in
handheld devices. Applications with series connected
LEDs ensure constant and identical LED currents re-
sulting in uniform brightness. A continuous LED output
current is setup using the FB pin regulated voltage
across an external sense resistor, R
FB
connected be-
tween the FB pin and ground. The integrated open load
protection circuitry prevents damage resulting from an
open circuit condition. The low 95mV feedback voltage
minimises power losses in the current setting resistor
which improves efficiency. The HT7937 has a high
switching frequency of up to 1.2MHz which permits the
use of lower value extremely small outline inductor and
filter capacitor.
The HT7937 is supplied in a space-saving, 6-lead
SOT23-6 package type.
Block Diagram
O V P
2 8 V
S W
S H D N
F B
C o n tro l
L o g ic
9 5 m V
å
G N D
1 .2 M H z
O s c illa to r
V IN
Rev 1.10
1
January 18, 2010
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
