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MAX16929

Automotive TFT-LCD Power Supply with Boost

Converter and Gate Voltage Regulators

the device’s built-in digital soft-start functions reduce the

number of external components required while control-

ling inrush currents. The output voltage can be set from

The regulator controls the output voltage by modulat-

ing the duty cycle (D) of the internal power MOSFET in

each switching cycle. The duty cycle of the MOSFET is

approximated by:

IN

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.

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 voltage at

COMPV sets the peak inductor current. As the load var-

ies, the error amplifier sources or sinks current to the

COMPV output accordingly to produce the peak induc-

tor current necessary to service the load. To maintain

stability at high duty cycles, a slope-compensation sig-

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

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

clock, the controller turns on the n-channel MOSFET and

applies 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.

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

MAX16929