���������������������������������������������������������������� Maxim Integrated Products 12

MAX16929

Automotive TFT-LCD Power Supply with Boost

Converter and Gate Voltage Regulators

Detailed Description

The MAX16929 is a highly integrated power supply for

automotive TFT-LCD applications. The device integrates

one buck converter, 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 buck converter is designed to

shut down when its die temperature reaches +175NC

(typ), while the boost circuitry does so at +165NC (typ).

Each resumes normal operation once its die temperature

has fallen 15NC below its respective thermal shutdown

temperature.

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/Selector Guide table.

Buck Converter

The device features a current-mode buck converter with

an integrated high-side FET, which requires no external

compensation network. The buck converter regulates the

output voltage to within Q3% in continuous mode over

line and load conditions. The high 2.1MHz (typ) switching

frequency allows for small external components, reduced

output ripple, and guarantees no AM interference.

A power-good (PGOOD) indicator is available to moni-

tor output-voltage quality. The enable input allows the

device to be placed in shutdown, reducing supply cur-

rent to 70FA.

The buck converter comes with a preset output voltage

of either 3.3V or 5V, and can deliver either 1.2A or 2A to

the output.

Enable (ENB)

Connect ENB to INB for always-on operation. ENB is also

compatible with 3.3V logic systems and can be con-

trolled through a microcontroller or by automotive KEY or

CAN inhibit signals.

Internal 5V Regulator (AVL)

AVL is an internal 5V regulator that supplies power to the

buck controller and charges the boost capacitor. After

(max), LXB starts switching. Bypass AVL to GND with a

1FF ceramic capacitor.

Spread-Spectrum Modulation

The buck converter features spread-spectrum operation

that varies the internal operating frequency of the buck

converter by +6% relative to the switching frequency of

2.1MHz (typ).

Soft-Start

The buck converter features an internal soft-start timer.

The output voltage takes 3.9ms to ramp up to its set

voltage. If a short circuit or undervoltage is encountered

after the soft-start timer has expired, the device enters

hiccup mode, during which soft-start is reattempted

every 16ms. This process repeats until the short circuit

has been removed.

Overcurrent Protection

The device enters hiccup mode in one of three ways. If

eight consecutive current limits are detected and the out-

put is below 77% of its nominal value, the buck converter

enters hiccup mode. The converter enters hiccup mode

immediately if the output is short circuited to ground

(output below 1V). Additionally, the device enters hiccup

mode if 256 consecutive overcurrent events are detected

when the output is greater than 77% of its nominal value.

In hiccup mode, the buck controller idles for 16ms before

reattempting soft-start.

Power Good (PGOOD)

When an overcurrent condition causes the buck output to

fall below 92% of its set voltage, the open-drain power-

good indicator output (PGOOD) asserts low. PGOOD

deasserts once the output voltage has risen above 95%

of its set voltage.

PGOOD serves as a general fault indicator for all the

converters and regulators. Besides indicating an under-

voltage on the buck output, it also indicates any of the

faults listed in the Fault Conditions and PGOOD section.

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 inductors and

ceramic capacitors to minimize the thickness of LCD panel

designs. The integrated low on-resistance MOSFET and