Detailed description – Rainbow Electronics MAX8712 User Manual

Page 10

MAX8710/MAX8711/MAX8712

Low-Cost Linear-Regulator
LCD Panel Power Supplies

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PIN

NAME

MAX8710

MAX8711

MAX8712

FUNCTION

FBP

Positive Charge-Pump Feedback Input. Connect FBP to the center of a resistive
voltage-divider between the positive charge-pump regulator output and GND to
set the regulator output voltage. Place the divider within 5mm of FBP. FBP is
internally pulled to GND by a 10

Ω

resistor in shutdown.

SHDN

Active-Low Shutdown Control Input. Pull SHDN low to turn off all sections of the
device except REF. Pull SHDN high to enable the device. Cycle SHDN to reset the
device after a fault.

CTL

—

High-Voltage Switch-Control Block Timing Control Input. See the Switch Control
section for details.

FBL

Linear-Regulator Feedback Input. Connect FBL to the center of a resistive
voltage-divider between the linear-regulator output and GND to set the linear-
regulator output voltage. Place the divider within 5mm of FBL.

MODE

—

High-Voltage Switch-Control Block-Mode Selection Input and Timing-Adjustment
Input. See the Switch Control section for details. MODE is high impedance when it
is connected to REF. MODE is internally pulled to GND by a 1k

Ω

resistor during

REF UVLO, when V

DLP

< 2.5V, or in shutdown.

DLP

Positive Charge-Pump Startup Delay and High-Voltage Switch Delay Input.
Connect a capacitor from DLP to GND to set the delay time. A 5µA current source
charges C

DLP

. DLP is internally pulled to GND by a 10

Ω

resistor in shutdown.

FBN

Negative Charge-Pump Feedback Input. Connect FBN to the center of a resistive
voltage-divider between the negative output and REF to set the output voltage.
Place the divider within 5mm of FBN. FBN is internally pulled to GND through a
10

Ω

resistor in shutdown.

SRC

—

Switch Input. Source of the internal high-voltage P-channel MOSFET connected to
GON.

Pin Description (continued)

Typical Operating Circuit

Figures 1, 2, and 3 are the Typical Operating Circuits of
the MAX8710, MAX8711, and MAX8712 for generating
power rails in TFT LCD panels. The input voltage range
is from 10.8V to 13.2V. The AVDD output is 10V at
300mA, the V

GON

output is 27V at 20mA, and the

GOFF

output is -5V at 50mA.

Detailed Description

The MAX8710/MAX8711/MAX8712 include a high-perfor-
mance linear regulator, a positive charge-pump regula-
tor, a negative charge-pump regulator, and built-in
power-up sequence control. The MAX8710 and
MAX8711 also include a high-current operational amplifi-
er. Additionally, the MAX8710 provides logic-controlled
high-voltage switches to control the positive charge-
pump output. The linear regulator directly steps down the

input voltage to generate the source-driver ICs’ supply
voltage. The two built-in charge-pump regulators are
used to generate the TFT gate-on and gate-off supplies.
The high-current operational amplifier is typically used to
drive the LCD backplane (VCOM) and features high out-
put current (150mA), fast slew rate (12V/µs), and wide
bandwidth (12MHz). Its rail-to-rail inputs and output maxi-
mize flexibility.

Linear Regulator

MAX8710/MAX8711/MAX8712 contain a linear regulator
that uses an internal PNP pass transistor to supply load
currents up to 300mA. Connect an external resistive volt-
age-divider between the regulator output and GND with
the midpoint connected to FBL to adjust the linear-regu-
lator output. An error amplifier compares the FBL voltage
with the 2.5V internal reference voltage and amplifies the
difference. If the feedback voltage is higher than the