MAX16928AGUP/V+ Maxim Integrated, MAX16928AGUP/V+ Datasheet - Page 14

• Manufacturer Part Number: MAX16928AGUP/V+
• Description: LCD Drivers Automotive TFT Power Supply
• Manufacturer: Maxim Integrated

Specifications of MAX16928AGUP/V+

• Rohs: yes

is the forward-voltage drop of the charge-pump diode,
V
of the boost converter, and V
margin for the regulator. Use V
negative voltage regulator and V
for the positive-gate voltage regulator.
Increasing the flying capacitor (C
effective source impedance and increases the output
current capability. Increasing the capacitance indefi-
nitely has a negligible effect on output current capability
because the internal switch resistance and the diode
impedance place a lower limit on the source impedance.
A 0.1FF ceramic capacitor works well in most low-current
applications. The voltage rating of the flying capacitors
for the positive charge pump should exceed V
that for the negative charge pump should exceed the
magnitude of V
Increasing the output capacitance or decreasing the ESR
reduces the output-ripple voltage and the peak-to-peak
transient voltage. With ceramic capacitors, the output-
voltage ripple is dominated by the capacitance value.
Use the following equation to approximate the required
output capacitance for the noninverting charge pump
connected to CP:
where C
pump, D is the duty cycle of the boost converter, I
is the load current of the charge pump, f
ing frequency of the boost converter, and V
the peak-to-peak value of the output ripple.
For the inverting charge pump connected to CN, use the
following equation to approximate the required output
capacitance:
where C
pump, D is the duty cycle of the boost converter,
I
is the switching frequency of the boost converter, and
Maxim Integrated
LOAD_CN
SCHOTTKY
OUT_CP
OUT_CN
Automotive TFT-LCD Power Supply with Boost
is the load current of the charge pump, f
is the forward drop of the Schottky diode
C
C
OUT_CN
OUT_CP
CN
is the output capacitor of the charge
is the output capacitor of the charge
.
Charge-Pump Output Capacitor
≥
≥
f
f
(1-D) I
SW
SW
Converter and Gate Voltage Regulators
D I
×
×
×
DROPOUT
×
V
V
LOAD_CP
DROPOUT
DROPOUT
RIPPLE_CP
RIPPLE_CN
LOAD_CN
X
) value lowers the
Flying Capacitors
SW
is the dropout
= 0.3V for the
= 2V at 20mA
is the switch-
RIPPLE_CP
LOAD_CP
CP
, and
SW
is
V
ripple.
Use high-speed silicon switching diodes with a current
rating equal to or greater than two times the average
charge-pump input current. If it helps avoid an extra
stage, some or all of the diodes can be replaced with
Schottky diodes with an equivalent current rating.
The output voltage of the positive-gate voltage regula-
tor can be adjusted by using a resistive voltage-divider
formed by R
the output and FBGH, and connect R
FBGH and GND. Select R
range. Calculate R
where V
(the regulated feedback voltage for the regulator). Place
both resistors as close as possible to the device.
Avoid excessive power dissipation within the internal
pMOS device of the regulator by paying attention to the
voltage drop across the drain and source. The amount of
power dissipation is given by:
where V
age applied to the drain, V
voltage, and I
The positive-gate voltage regulator (GH) requires a mini-
mum output capacitance for stability. For an output volt-
age of 5V to (V
15mA, use a minimum capacitance of 0.47FF.
The output voltage of the negative-gate voltage regula-
tor can be adjusted by using a resistive voltage-divider
formed by R
REF and FBGL and connect R
and the collector of the external npn transistor. Select
RIPPLE_CN
GH
CP
is the desired output voltage and V
is the noninverting charge-pump output volt-
P
R
TOP
TOP
GL
is the peak-to-peak value of the output
LOAD(MAX)
TOP
Negative-Gate Voltage Regulator
CP
Positive-Gate Voltage Regulator
= (V
and R
and R
=
- 2V) and an output current of 10mA to
TOP
R
CP
BOTTOM
BOTTOM
BOTTOM
with the following equation:
- V
Charge-Pump Rectifier Diodes
is the maximum load current.
BOTTOM
GH
GH
) × I
Output Voltage Selection
Output Voltage Selection
×
. Connect R
. Connect R
MAX16928
BOTTOM
(
Stability Requirements
is the regulated output
V
LOAD(MAX)
V
FBGH
GH
in the 10kI to 50kI
BOTTOM
−
between FBGL
1)
TOP
TOP
FBGH
between
between
between
= 1V
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