MAX8798AETX+T Maxim Integrated Products, MAX8798AETX+T Datasheet - Page 21

• Manufacturer Part Number: MAX8798AETX+T
• Description: Display Drivers Internal-Switch Boos t Regulator with Int
• Manufacturer: Maxim Integrated Products

Specifications of MAX8798AETX+T

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The DISH input controls a switch between GOFF and
GND. When DISH is pulled below ground by at least
1V, GOFF is rapidly discharged to GND. Typically,
DISH is capacitively coupled to IN so that if IN falls
suddenly, GOFF is discharged to blank the display
(Figure 3).
The VCOM calibrator is a solid-state alternative to
mechanical potentiometers used for adjusting the LCD
backplane voltage (VCOM) in TFT LCD displays. OUT
attaches to the external resistive voltage-divider at POS
and sinks a programmable current (I
VCOM level (Figure 6). An internal 7-bit DAC controls the
sink current and allows the user to increase or decrease
the VCOM level. The DAC is ratiometrically relative to
V
The user can store the DAC setting in an internal
EEPROM. On power-up, the EEPROM presets the DAC
to the last stored setting. The 2-wire I
between the system controller and the programming cir-
cuit adjusts the DAC and programs the EEPROM when
WPN is high.
Figure 6. VCOM Calibrator Functional Diagram
BOOST
Integrated 3-Channel Scan Driver for TFT LCDs
and is monotonic over all operating conditions.
I
2
C BUS
GOFF Rapid Discharge Function
______________________________________________________________________________________
V
DD
Internal-Switch Boost Regulator with
SDA
SCL
SCLS
WPP
VCOM Calibrator
WPN
OUT
), which sets the
(DISH Input)
INTERFACE
V
CONTROL
DD
2
V
C interface
I 2 C
DD
REGULATOR
7
LINEAR
7
DAC
GON
EEPROM
BLOCK
VGON
The resistive voltage-divider and the BOOST supply set
the maximum value of VCOM. OUT sinks current from the
voltage-divider to reduce the POS voltage level and
VCOM output. The external resistor at SET (R
full-scale sink current and the minimum value of VCOM.
The GON input provides the high voltage required to
program the EEPROM. To allow programming, V
connected to the TFT LCD V
be between 16.1V and 35V. EEPROM programming is
disabled when V
V
with a 0.1µF or greater capacitor.
The thermal-overload protection prevents excessive
power dissipation from overheating the device. When
the junction temperature exceeds T
mal sensor immediately activates the fault protection
that shuts down the step-up regulator, switch control
block, operational amplifier, and the internal linear reg-
ulator, allowing the device to cool down. Once the
device cools down by approximately 15°C, cycle the
input voltage (below the UVLO falling threshold) to
clear the fault latch and reactivate the device.
The thermal-overload protection protects the controller
in the event of fault conditions. For continuous opera-
tion, do not exceed the absolute maximum junction
temperature rating of T
GON
19R
R
to PGND or BOOST (that is bypassed to PGND)
Thermal-Overload Protection
GON
J
is below 15.5V (typ). Bypass
= +150°C.
BOOST
VCOM
NEG
OUT
POS
SET
GON
supply. V
V
MAIN
J
= +160°C, a ther-
VCOM
R3
R4
R
SET
SET
GON
) sets the
GON
should
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is