Selector guide – Rainbow Electronics MAX1885 User 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;