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MAX16929

Automotive TFT-LCD Power Supply with Boost

Converter and Gate Voltage Regulators

Boost Converter

Inductor Selection

Three key inductor parameters must be specified for

operation with the device: inductance value (L), induc-

To determine the inductance value, select the ratio of

inductor peak-to-peak ripple current to average input

current (LIR) first. For LIR values that are too high, the

Use high-valued inductors to achieve low LIR values.

Typically, inductance is proportional to resistance for a

for very low LIR values. A good compromise between

size and loss is to select a 30%-to-60% peak-to-peak

ripple current to average-current ratio. If extremely thin

high-resistance inductors are used, as is common for

LCD-panel applications, the best LIR can increase

between 0.5 and 1.0. The size of the inductor is deter-

mined as follows:

O

O

INA

INP

INP

SW

INA

V

I

V

D

L =

and I

=

LIR I

f

V

×

×

×

×

η

INA

O

V

D =1

V

η

−

current, E is the efficiency of the boost converter, D is the

of the boost converter). The efficiency of the boost

converter can be estimated from the Typical Operating

Characteristics and accounts for losses in the internal

Capacitor Selection

The input and output filter capacitors should be of a low-

ESR type (tantalum, ceramic, or low-ESR electrolytic) and

INP

RMS

LIR I

I

=

12

×

for the input capacitor

2

RMS

O

LIR

D +

12

I

=I

1 D

−

for the output capacitor

given above.

The output voltage contains a ripple component whose

peak-to-peak value depends on the value of the ESR and

capacitance of the output capacitor and is approximately

given by:

D

ESR

INP

ESR

LIR

V

=I

(1+

) R

2

∆

×

×

O

CAP

OUT SW

I

D

V

=

C

f

×

∆

×

given above.

Rectifier Diode

The catch diode should be a Schottky type to minimize

its voltage drop and maximize efficiency. The diode must

be capable of withstanding a reverse voltage of at least

rating greater than:

given above. In addition ensure that the peak current rat-

ing of the diode is greater than:

INP

LIR

I

1+

2





× 







Output-Voltage Selection

The output voltage of the boost converter can be adjust-

O

TOP

BOTTOM

FBP

V

R

= R

(

1)

V

×

−

1V. Place both resistors as close as possible to the device

Loop Compensation

the integrator zero to maintain loop stability. For low-ESR

output capacitors, use Table 3 to select the initial values