MAX1885EUP-T Maxim Integrated, MAX1885EUP-T Datasheet - Page 19

• Manufacturer Part Number: MAX1885EUP-T
• Description: LCD Drivers Quad-Output TFT LCD DC-DC Converter with Buffer
• Manufacturer: Maxim Integrated

Specifications of MAX1885EUP-T

• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Package / Case: TSSOP-20
• Mounting Style: SMD/SMT

The MAX1778/MAX1880–MAX1885 are highly efficient
multiple-output power supplies for thin-film transistor
(TFT) liquid crystal display (LCD) applications. The
devices contain one high-power step-up converter, two
low-power charge pumps, an operational transconduc-
tance amplifier (VCOM buffer), and a low-dropout linear
regulator. The primary step-up converter uses an internal
N-channel MOSFET to provide maximum efficiency and
to minimize the number of external components. The out-
put voltage of the main step-up converter (V
be set from V
The dual charge pumps (MAX1778/MAX1880–MAX1882
only) independently regulate a positive output (V
and a negative output (V
use external diode and capacitor stages (as many
stages as required) to regulate output voltages from -
40V to +40V. A unique control scheme minimizes output
ripple as well as capacitor sizes for both charge pumps.
Figure 1. Typical Application Circuit
Maxim Integrated
V
IN
IN
INPUT
= 3.3V
to 13V with external resistors.
V
LDOOUT
V
NEGATIVE
NEG
4.7µF
C
= -5V
TO LOGIC
IN
LDO
= 5V
Detailed Description
NEG
1.0µF
4.7µF
C
LDO
C3
). These low-power outputs
100kΩ
R
RDY
0.22µF
49.9kΩ
C
0.22µF
REF
MAIN
R8
(8V)
200kΩ
49.9kΩ
R5
C1
R6
MAX1778/MAX1880–MAX1885
0.1µF
R7
150kΩ
C2
MAIN
Quad-Output TFT LCD DC/DC
IN
SHDN
RDY
SUPL
LDOOUT
FBL
DRVN
FBN
REF
INTG
FLTSET
PGND
) can
POS
MAX1778
)
6.8µH
L1
A resistor-programmable 40mA linear regulator
(MAX1778/MAX1881/MAX1883/MAX1884 only) can
provide preregulation or postregulation for any of the
supplies. For higher current applications, an external
transistor can be added.
Additionally, the VCOM buffer provides a high current
output that is ideal for driving capacitive loads, such as
the backplane of a TFT LCD panel. The positive feed-
back input features dual-mode operation, allowing this
input to be connected to an internal 50% resistive-
divider between the buffer’s supply voltage and
ground, or externally adjusted for other voltages.
Also included in the MAX1778/MAX1880–MAX1885 is a
precision 1.25V reference that sources up to 50µA,
logic shutdown, soft-start, power-up sequencing,
adjustable fault detection, thermal shutdown, and an
active-low, open-drain ready output.
BUFOUT
Converters with Buffer
SUPB
SUPN
SUPP
DRVP
TGND
BUF+
BUF-
GND
FBP
LX
FB
0.1µF
49.9kΩ
0.1µF
274kΩ
C4
C4
R4
49.9kΩ
R2
R2
750kΩ
R3
C
1.0µF
BUF
BUFFER OUTPUT
V
BUFOUT
C
(2) 4.7µF
C5
1.0µF
OUT
= V
SUPB
MAIN
V
MAIN
C7
1.0µF
/2
= 8V
POSITIVE
V
POS
= 20V
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