MAX16928CGUP/V+ Maxim Integrated, MAX16928CGUP/V+ Datasheet - Page 12

• Manufacturer Part Number: MAX16928CGUP/V+
• Description: LCD Drivers Automotive TFT Power Supply
• Manufacturer: Maxim Integrated

Specifications of MAX16928CGUP/V+

• Rohs: yes

which again makes I
A good compromise between size and loss is to select a
30%-to-60% peak-to-peak ripple current to average-current
ratio. If extremely thin high-resistance inductors are used,
as is common for LCD-panel applications, the best LIR can
increase between 0.5 and 1.0. The size of the inductor is
determined as follows:
where V
I
current, E is the efficiency of the boost converter, D is the
duty cycle, and f
of the boost converter). The efficiency of the boost
converter can be estimated from the
Characteristics
switch, catch diode, inductor R
The input and output filter capacitors should be of a low-
ESR type (tantalum, ceramic, or low-ESR electrolytic) and
should have I
where I
given above.
The output voltage contains a ripple component whose
peak-to-peak value depends on the value of the ESR and
capacitance of the output capacitor and is approximately
given by:
where I
given above.
Maxim Integrated
O
is the output current, I
I
RMS
INA
INA
INA
I
L
RMS
Automotive TFT-LCD Power Supply with Boost
=I
and D are the input current and duty cycle
and D are the input current and duty cycle
is the input voltage, V
LIR I
=
∆
RMS
=
O
DV
V
LIR I
ESR
and accounts for losses in the internal
V
×
RIPPLE
SW
INA
D +
∆
INA
ratings greater than:
V
×
1 D
2
12
=I
CAP
R losses high for very low LIR values.
is 2.2MHz (the switching frequency
−
LIR
×
INA
D
×
12
INA
D
f
=
= DV
SW
2
=
INA
1- V
for the input capacitor
×
Converter and Gate Voltage Regulators
C
for the output capacitor
η
(1+
and I
V
OUT
ESR
is the average boost input
I
O
O
INA
DC
LIR
×
2
O
×
INA
+ DV
, and capacitor ESR.
D
f
) R
SW
is the output voltage,
Capacitor Selection
×
Typical Operating
CAP
ESR
V
η
O
V
INA
×
I
O
The catch diode should be a Schottky type to minimize
its voltage drop and maximize efficiency. The diode must
be capable of withstanding a reverse voltage of at least
V
rating greater than:
where I
given above. In addition ensure that the peak current rat-
ing of the diode is greater than:
The output voltage of the boost converter can be adjust-
ed by using a resistive voltage-divider formed by R
and R
FBP and connect R
Select R
R
where V
1V. Place both resistors as close as possible to the device
and connect R
Choose R
gain for fast transient response. Choose C
the integrator zero to maintain loop stability. For low-ESR
output capacitors, use
for R
lel with R
Table 2. Compensation Component Values
SH
TOP
R
C
C
. The diode should have an average forward current
COMPV
COMPV
COMPV
COMPI
I
V
V
SH
with the following equation:
P
BOTTOM
L (µH)
INA
SH
IN
INA
FBP
BOTTOM
COMPV
(mA)
(W)
(V)
COMPV
(V)
(pF)
(kI)
and D are the input current and duty cycle
, the boost converter’s feedback set point, is
(pF)
and C
R
. Connect R
BOTTOM
TOP
+ C
in the 10kI to 50kI range. Calculate
COMPV
to set the high-frequency integrator
= R
I
COMPV
D
I
BOTTOM
INA
= I
BOTTOM
Table 2
to the analog ground plane.
. Use a 22pF capacitor in paral-
INA
× 
1.75
200
220
820
3.3
TOP


33
.
8
5
1+
× (1-D)
Output Voltage Selection
between FBP and GND.
LIR
to select the initial values
×
between the output and
MAX16928
2
(
V



Loop Compensation
V
FBP
O
−
Rectifier Diode
1)
COMPV
3.75
200
180
330
18
39
5
5
to set
TOP
12