MAX1516 Datasheet, PDF(15/26 Page) Maxim Integrated Products – TFT-LCD DC-DC Converters with Operational Amplifiers

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MAX1516 Datasheet, PDF (15/26 Pages) Maxim Integrated Products – TFT-LCD DC-DC Converters with Operational Amplifiers

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TFT-LCD DC-DC Converters with

Operational Amplifiers

CLOCK

RESET DOMINANT

ILIM

COMPARATOR

SLOPE COMP

PWM

COMPARATOR

SOFT-

START

VLIMIT

Î£

CURRENT

SENSE

PGND

OSCILLATOR

FAULT

COMPARATOR

TO FAULT LATCH

ERROR AMP

1.0V

Figure 3. Step-Up Regulator Functional Diagram

1.236V

COMP

This discharge condition forces the current through the

inductor to ramp back down, transferring the energy

stored in the magnetic field to the output capacitor and

the load. The MOSFET remains off for the rest of the

clock cycle.

Gate-On Linear-Regulator Controller, REG P

The gate-on linear-regulator controller (REG P) is an

analog gain block with an open-drain n-channel output.

It drives an external pnp pass transistor with a 6.8kâ¦

base-to-emitter resistor (Figure 1). Its guaranteed base-

drive sink current is at least 1mA. The regulator including

Q1 in Figure 1 uses a 0.47ÂµF ceramic output capacitor

and is designed to deliver 20mA at 24V. Other output

voltages and currents are possible with the proper pass

transistor and output capacitor. See the Pass-Transistor

Selection and Stability Requirements sections.

REG P is typically used to provide the TFT-LCD gate

driversâ gate-on voltage. Use a charge pump with as

many stages as necessary to obtain a voltage exceed-

ing the required gate-on voltage (see the Selecting the

Number of Charge-Pump Stages section). Note the

voltage rating of the DRVP is 28V. If the charge-pump

output voltage can exceed 28V, an external cascode

npn transistor should be added as shown in Figure 4.

Alternately, the linear regulator can control an interme-

diate charge-pump stage while regulating the final

charge-pump output (Figure 5).

REG P is enabled after the REF voltage exceeds 1.0V.

Each time it is enabled, the controller goes through a

soft-start routine that ramps up its internal reference

DAC in 128 steps.

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