Datasheet

MAX8795A
TFT-LCD DC-DC Converter with
Operational Amplifiers
______________________________________________________________________________________ 19
C
DEL
. Once the C
DEL
capacitor voltage exceeds 1.25V
(typ), the switch-control block is and op amps are enabled
as shown in Figure 6. After the switch-control block is
enabled, COM can be connected to SRC or DRN through
the internal p-channel switches, depending upon the state of
CTL. Before startup and when IN is less than V
UVLO
, DEL is
internally connected to AGND to discharge C
DEL
. Select
C
DEL
to set the initial start-up delay and the switch-control
block startup delay times using the following equation:
Switch-Control Block
The switch-control input (CTL) is not activated until all
four of the following conditions are satisfied: the input
voltage exceeds V
UVLO
, the soft-start routine of all the
regulators is complete, there is no fault condition detect-
ed, and V
DEL
exceeds its turn-on threshold. Once acti-
vated and if CTL is high, the 5Ω internal p-channel
switch (Q1) between COM and SRC turns on and the
CDELAYTIME
IA
V
DEL
=×
µ
_
.
6
125
2.25V
1.05V
INPUT
VOLTAGE
OK
SOFT-
START
BEGINS
SOFT-
START
ENDS
SWITCH
CONTROL
ENABLED
12ms
V
IN
V
REF
V
MAIN
V
GON
V
GOFF
1.25V
V
DEL
Figure 6. Power-Up Sequence
MAX8795A
FB OK
FBP OK
FBN OK
2.25V
5µA
REF
DRN
COM
SRC
Q1
Q2
CTL
DEL
IN
Figure 7. Switch-Control Block