MAX16929 Datasheet, PDF (13/25 Pages) Maxim Integrated Products – Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators

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
V_INA to 18V with an external resistive voltage-divider.
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:
D =1− ^ηVIN
V_O
where V_IN 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.
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.
CLOCK
ILIM
COMPARATOR
LOGIC AND
DRIVER
LXP
PGNDP
2.2MHz
OSCILLATOR
PWM
COMPARATOR
TO FAULT LOGIC
FAULT
COMPARATOR
MAX16929
SOFT-
START
VLIMIT
Σ
CURRENT
SENSE
SLOPE
COMP
ERROR
AMP
0.85V
1V
COMPI
FBP
COMPV
Figure 1. Boost Converter Functional Diagram
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