MAX16928_12 Datasheet, PDF (8/20 Pages) Maxim Integrated Products – Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators

MAX16928
Automotive TFT-LCD Power Supply with Boost
Converter and Gate Voltage Regulators
Pin Description (continued)
PIN
NAME
FUNCTION
13
GH Positive-Gate Voltage Regulator Output
14
DRVN
Negative-Gate Voltage Regulator Driver Output. DRVN is the open drain of an internal p-channel FET.
Connect DRVN to the base of an external npn pass transistor.
15
GND Analog Ground
16
COMPI
Boost Slope Compensation Connection. Connect a capacitor between COMPI and GND to set the
slope compensation.
17
FBGH
Positive-Gate Voltage Regulator Feedback Input. FBGH is regulated to 1V. Connect FBGH to the center
of a resistive divider connected between GH and GND.
Negative-Gate Voltage Regulator Feedback Input. FBGL is regulated to 0.25V. Connect FBGL to the
18
FBGL center of a resistive divider connected between REF and the output of the negative-gate voltage
regulator.
19
REF 1.25V Reference Output. Bypass REF to GND with a 0.1FF ceramic capacitor.
20
SEQ
Sequencing Input. SEQ has an internal 500kI pulldown resistor. SEQ determines the sequence in
which V_GH and V_GL power up. See Table 1 for supply sequencing options.
—
EP
Exposed Pad. Connect to a large contiguous copper ground plane for optimal heat dissipation. Do not
use EP as the only electrical ground connection.
Detailed Description
The MAX16928 is a highly integrated power supply for
automotive TFT-LCD applications. The device integrates
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 device is designed to shut down
when its die temperature reaches +165NC (typ) and to
resume normal operation once its die temperature has
fallen 15NC.
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 table.
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 induc-
tors and ceramic capacitors to minimize the thickness
of LCD panel designs. The integrated low on-resistance
MOSFET and the device’s built-in digital soft-start func-
tions reduce the number of external components required
while controlling inrush currents. The output voltage
can be set from V_INA to 18V with an external resistive
voltage-divider. The regulator controls the output voltage
by modulating the duty cycle (D) of the internal power
MOSFET in each switching cycle. The duty cycle of the
MOSFET is approximated by:
D =1− ^ηVINA
V_O
where V_INA is the voltage at INA, V_O = V_SH (the boost
output voltage), and E is the efficiency of the boost con-
verter as shown in the Typical Operating Characteristics.
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