MAX16929
Automotive TFT-LCD Power Supply with Boost
Converter and Gate Voltage Regulators
where:
f POLE_IN =
1
2 π × C IN × (R BE /R IN )
Table 4. Minimum Output Capacitance vs. 
Output Voltage Range for Negative-Gate 
Voltage Regulator (I OUT  = 10mA to 15mA)
C IN =
, R IN =
f POLE_IN =
f POLE =
f POLE_FBGL =
f ZERO_ESR =
g m h FE
2 π f T g m
g m is the transconductance of the pass transistor, and
f T is the transition frequency. Both parameters can be
found in the transistor’s data sheet. Because R BE is
much greater than R IN , the above equation can be
simplified:
1
2 π × C IN × R IN
Substituting for C IN and R IN yields:
f T
h FE
4) Next, calculate the pole set by the regulator’s feed-
back resistance and the capacitance between FBGL
and GND (including stray capacitance):
1
2 π × C FBGL × (R TOP /R BOTTOM )
where C FBGL is the capacitance between FBGL and
GND and is equal to 30pF, R TOP is the upper resistor
of the regulator’s feedback divider, and R BOTTOM is
the lower resistor of the divider.
5) Next, calculate the zero caused by the output capaci-
tor’s ESR:
1
2 π × C OUT_LR × R ESR
where R ESR is the equivalent series resistance of
C OUT_LR . To ensure stability, make C OUT_LR large
enough so the crossover occurs well before the poles
and zero calculated in steps 2 to 5. The poles in steps
3 and 4 generally occur at several MHz and using
ceramic capacitors ensures the ESR zero also occurs
at several MHz. Placing the crossover frequency below
500kHz is sufficient to avoid the amplifier delay pole
OUTPUT VOLTAGE  MINIMUM OUTPUT 
RANGE CAPACITANCE (μF)
-2V R V GL R  -4V 2.2
-5V R V GL R -7V 1.5
-8V R V GL R -13V 1
Applications Information
Power Dissipation
An IC’s maximum power dissipation depends on the ther-
mal resistance from the die to the ambient environment
and the ambient temperature. The thermal resistance
depends on the IC package, PCB copper area, other
thermal mass, and airflow. More PCB copper, cooler
ambient air, and more airflow increase the possible dis-
sipation, while less copper or warmer air decreases the
IC’s dissipation capability. The major components of
power dissipation are the power dissipated in the buck
converter, boost converter, positive-gate voltage regula-
tor, negative-gate voltage regulator, and the 1.8V/3.3V
regulator controller.
Buck Converter
In the buck converter, conduction and switching losses
in the internal MOSFET are dominant. Estimate these
losses using the following formula:
P LXB ≈ [(I OUTB × √ D ) 2 × R DS_ON(LXB) ] + [0.5 × V INB ×
I OUTB × (t R + t F ) × f SWB ]
where I OUTB is the output current, D is the duty cycle
of the buck converter, R DS_ON(LXB) is the on-resistance
of the internal high-side FET, V INB is the input voltage,
(t R + t F) is the time is takes for the switch current and
voltage to settle to their final values during the rising and
falling transitions, and f SWB is the switching frequency
of the buck converter. R DS_ON(LXB) is 180m I (typ) and
(t R + t F) is 4.4ns + 4.6ns = 9ns at V INB = 12V.
and generally works well, unless unusual component
choices or extra capacitances move one of the other
poles or the zero below 1MHz.
Table 4 is a list of recommended minimum output capaci-
tance for the negative-gate voltage regulator and are
applicable for output currents in the 10mA to 15mA range.
 ????????????????????????????????????????????????????????????????   Maxim Integrated Products     21
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