MAX9550 Maxim, MAX9550 Datasheet - Page 6

• Manufacturer Part Number: MAX9550
• Description: The MAX9550/MAX9551/MAX9552 provide a VCOM source for TFT LCDs
• Manufacturer: Maxim

High-Current VCOM Drive Buffers
for TFT LCDs
The MAX9550/MAX9551/MAX9552 operational transcon-
ductance amplifiers (OTA) hold the VCOM voltage sta-
ble while providing the ability to source and sink a high
current quickly (800mA typ) into a capacitive load such
as the backplane of a TFT-LCD panel. The output settles
to within 0.1% in less than 2µs. The fast settling time is
achieved by increasing the transconductance of the
buffer as the output current increases (see the Typical
Operating Characteristics).
In addition, the MAX9550/MAX9551/MAX9552 directly
drive the capacitive load in the VCOM layer of the
TFT LCD without the need for a series resistor.
The MAX9550/MAX9551/MAX9552 unity-gain band-
width is:
where C
is the transconductance.
Figure 1. Settling Time Test Circuit
6
_______________________________________________________________________________________
OUT
**R
*PLACE 4.7µF AND 0.1µF CAPACITORS AS CLOSE TO PIN AS POSSIBLE.
is the capacitive load at the output and g
V
NOTE: PLACE C
REF
S
INCLUDES THE GENERATOR RESISTANCE.
SUPPLY
GBW = g
16V
SENSE THE FEEDBACK LOOP CONNECTION AS SHOWN.
Detailed Description
*C2 = 0.1µF
L
AS CLOSE TO OUT PIN AS POSSIBLE AND KELVIN
M
IN+
IN-
/ 2πC
SUPPLY
OUT
16V
MAX9550
GND
V
DD
OUT
*C1 = 4.7µF
C
L
= 1µF
M
V
OUT
To insure buffer stability, place a 1µF low-ESR capaci-
tor as close to the OUT pin as possible. However, this
value may be reduced if the TFT-LCD panel load pro-
vides some of the capacitance and the resistance in
series when this capacitance is low. Connect the feed-
back at OUT using a Kelvin connection at the low-ESR
capacitor.
The MAX9550/MAX9551/MAX9552 are capable of high
output currents and therefore, feature thermal-shutdown
protection with temperature hysteresis. When the die tem-
perature reaches +160°C, the devices shut down. When
the die cools down by 15°C, the devices turn on again.
Thermal Shutdown with Temperature
**R
S
0V TO 1.5V AT 50kHz
= 2.2Ω
TEST LOAD
C
S
= 0.1µF
Hysteresis