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MAX16928

Automotive TFT-LCD Power Supply with Boost

Converter and Gate Voltage Regulators

Figure 1 shows the functional diagram of the boost

regulator. An error amplifier compares the signal at

FBP to 1V and changes the COMPV output. The volt-

age at COMPV sets the peak inductor current. As the

load varies, the error amplifier sources or sinks current

to the COMPV output accordingly to produce the peak

inductor current necessary to service the load. To main-

tain stability at high duty cycles, a slope-compensation

signal (set by the capacitor at COMPI) is summed with

the current-sense signal. On the rising edge of the

internal clock, the controller sets a flip-flop, turning on

the n-channel MOSFET and applying the input voltage

across the inductor. The current through the inductor

ramps up linearly, storing energy in its magnetic field.

Once the sum of the current feedback signal and the

slope compensation exceeds the COMPV voltage, the

controller turns off the MOSFET. The inductor current

then flows through the diode to the output. The MOSFET

remains off for the rest of the clock cycle.

The external p-channel FET controlled by GATE protects

the output during fault conditions and provides True

Shutdown of the converter. Connect a pullup resistor

between GATE and INA (see the Boost Converter section

to select the value for the pullup resistor). Under normal

operation, GATE turns on the p-channel FET, connecting

the supply to the boost input. During a fault condition or

in shutdown, GATE is off and the pullup resistor turns off

the p-channel FET, disconnecting the supply from the

boost input.

Figure 1. Boost Converter Functional Diagram

LOGIC AND

DRIVER

LXP

CLOCK

PGNDP

FBP

COMPI

COMPV

ERROR

AMP

1V

0.85V

FAULT

COMPARATOR

TO FAULT LOGIC

2.2MHz

OSCILLATOR

PWM

COMPARATOR

COMPARATOR

SOFT-

START

CURRENT

SENSE

SLOPE

COMP

Σ

MAX16928