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MAX16928

Automotive TFT-LCD Power Supply with Boost

Converter and Gate Voltage Regulators

Pin Description (continued)

Detailed Description

The MAX16928 is a highly integrated power supply for

automotive TFT-LCD applications. The device integrates

one boost converter, one 1.8V/3.3V regulator controller,

one positive-gate voltage regulator, and one negative-

gate voltage regulator.

The device achieves enhanced EMI performance through

spread-spectrum modulation. Digital input control allows

the device to be placed in a low-current shutdown mode

and provides flexible sequencing of the gate voltage

regulators.

Internal thermal shutdown circuitry protects the device

from overheating. The device is designed to shut down

when its die temperature reaches +165NC (typ) and to

resume normal operation once its die temperature has

fallen 15NC.

The device is factory-trimmed to provide a variety of

power options to meet the most common automotive

TFT-LCD display power requirements, as outlined in the

Ordering Information table.

Boost Converter

The boost converter employs a current-mode, fixed-

frequency PWM architecture to maximize loop bandwidth

and provide fast transient response to pulsed loads

typical of TFT-LCD panel source drivers. The 2.2MHz

switching frequency allows the use of low-profile induc-

tors and ceramic capacitors to minimize the thickness

of LCD panel designs. The integrated low on-resistance

MOSFET and the device’s built-in digital soft-start func-

tions reduce the number of external components required

while controlling inrush currents. The output voltage

voltage-divider. The regulator controls the output voltage

by modulating the duty cycle (D) of the internal power

MOSFET in each switching cycle. The duty cycle of the

MOSFET is approximated by:

INA

O

V

D =1

V

η

−

output voltage), and E is the efficiency of the boost con-

verter as shown in the Typical Operating Characteristics.

PIN

NAME

FUNCTION

13

GH

Positive-Gate Voltage Regulator Output

14

DRVN

Negative-Gate Voltage Regulator Driver Output. DRVN is the open drain of an internal p-channel FET.

Connect DRVN to the base of an external npn pass transistor.

15

GND

Analog Ground

16

COMPI

Boost Slope Compensation Connection. Connect a capacitor between COMPI and GND to set the

slope compensation.

17

FBGH

Positive-Gate Voltage Regulator Feedback Input. FBGH is regulated to 1V. Connect FBGH to the center

of a resistive divider connected between GH and GND.

18

FBGL

Negative-Gate Voltage Regulator Feedback Input. FBGL is regulated to 0.25V. Connect FBGL to the

center of a resistive divider connected between REF and the output of the negative-gate voltage

regulator.

19

REF

1.25V Reference Output. Bypass REF to GND with a 0.1FF ceramic capacitor.

20

SEQ

Sequencing Input. SEQ has an internal 500kI pulldown resistor. SEQ determines the sequence in

—

EP

Exposed Pad. Connect to a large contiguous copper ground plane for optimal heat dissipation. Do not

use EP as the only electrical ground connection.