Rainbow Electronics MAX1885 - Manual (Page 35)

the Typical Operating Characteristics. Set the resistive
divider to precharge BUFOUT, matching the buffer’s
output set voltage:
These resistor values are selected to charge the output
capacitor close to the output set voltage before the
buffer starts up:
C R R
f
BUFOUT
OSC
( || ) 3 4
5000
≈
R R
V
V
SUPB
BUFOUT
3 4 1
=

 

−








MAX1778/MAX1880–MAX1885
Quad-Output TFT LCD DC-DC
Converters with Buffer
______________________________________________________________________________________ 35
PART
STEP-UP
SWITCHING
FREQUENCY
(Hz)
DUAL
CHARGE
PUMPS
LINEAR
REGULATOR
MAX1778 1M Yes Yes
MAX1880 1M Yes No
MAX1881 500k Yes Yes
MAX1882 500k Yes No
MAX1883 1M No Yes
MAX1884 500k No Yes
MAX1885 500k No No
Selector Guide
IN
BUFFER OUTPUT
V
BUFOUT = V SUPB /2
SHDN
SUPB
LX
L1
6.8 µH
INPUT
V IN = 3.3V
C1
0.22 µF
C OUT
(2) 4.7 µF
C IN
4.7 µF R1
274k Ω
R2
49.9k Ω
FB
BUFOUT
GND
BUF+
BUF-
REF
INTG
PGND
C REF
0.22 µF
MAX1778
C SUPB
1.0 µF
C BUF
1.0 µF
R3
10k Ω
R4
10k Ω
MAIN
V
MAIN = 8V
R3 = R4
[( )
-1
] V SUPB
V BUFOUT
Figure 11. VCOM Buffer Soft-Start;