Digitally Adjustable LCD Bias Supply
MAX749
____________________________Typical Operating Characteristics (continued)
(T
A
= +25°C, L = 47µH, unless otherwise noted.)
LOAD-TRANSIENT RESPONSE
LINE-TRANSIENT RESPONSE
OUTPUT
VOLTAGE
100mV
AC
/div
OUTPUT
VOLTAGE
100mV
AC
/div
LOAD
CURRENT
V
OUT
= -15V
TRANSISTOR = ZTX750
50µs/div
V
OUT
= -15V
TRANSISTOR = ZTX750
10mA/div
0mA
INPUT
VOLTAGE
1 V/div
50ms/div
V
OUT
= -15V
I
LOAD
= 5mA
TRANSISTOR = ZTX750
0V
______________________________________________________________Pin Description
PIN
1
NAME
V+
FUNCTION
+2V to +6V Input Voltage to power the MAX749 and external circuitry. When using an external
P-channel MOSFET, V+ must exceed the MOSFET’s gate threshold voltage.
Logic Input. When CTRL is high, a rising edge on ADJ increments an internal counter. When CTRL is
low, the counter is reset to mid-scale when ADJ is high. When ADJ is low, the counter does not
change (regardless of activity on CTRL) as long as V+ is applied.
Logic Input. When CTRL and ADJ are low, the MAX749 is shut down, but the counter is not reset.
When CTRL is low, the counter is reset to mid-scale when ADJ is high. The device is always on when
CTRL is high.
Feedback Input for output full-scale voltage selection. -V
OUT(MAX)
= (R
FB
) x (20µA) where R
FB
is
connected from FB to -V
OUT
. The device is in regulation when V
FB
= 0V.
Ground
Output Driver Low. Connect to DHI when using an external P-channel MOSFET. When using an
external PNP transistor, connect a resistor R
BASE
from DLOW to the base of the PNP to set the maxi-
mum base-drive current.
Output Driver High. Connect to the gate of the external P-channel transistor, or to the base of the
external PNP transistor.
Current-Sense Input. The external transistor is turned off when current through the sense resistor,
R
SENSE
, brings CS below V+ by 140mV (typ).
2
ADJ
3
CTRL
4
5
6
FB
GND
DLOW
7
8
DHI
CS
4
______________________________________________________________________________________
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