MAX8761ETG+ Maxim Integrated Products, MAX8761ETG+ Datasheet - Page 23

• Manufacturer Part Number: MAX8761ETG+
• Description: IC REG LINEAR LCD 24-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8761ETG+

• Applications: Converter, LCD Power Supplies
• Voltage - Input: 8 ~ 28 V
• Number Of Outputs: 1
• Voltage - Output: 5V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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 capacitor value:
where C
pump, I
pump, and V
value of the output ripple.
Use low-cost silicon switching diodes with a current rat-
ing 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 load current and the voltage difference between
the input and output determine the linear regulator’s
power dissipation as shown in the following equation:
For some applications, the input voltage to the linear
regulator is from a 19V adapter. To make a 10V output,
the voltage across the pass transistor is 9V. In this case,
the regulator’s power dissipation may exceed the dissi-
pation limit that the package can handle. In some other
applications, the load current may be much higher than
the regulator’s guaranteed 300mA output current for the
MAX8710/MAX8711/MAX8712 and 500mA for the
MAX8761.
The solution for such applications is to connect an exter-
nal pnp transistor with the internal pnp transistor in a
Darlington configuration as shown in Figure 8. The
external pass transistor must be able to handle most of
the power dissipation since most of the load current
flows through it. On the other hand, the power dissipat-
ed in the internal pass transistor is very low. The current-
limit circuit does not work if an external pass transistor is
used because the linear regulator only senses the cur-
rent of the internal pass transistor.
External Transistor for Higher Current
OUT_CP
LOAD_CP
P
DISSIPATION
C
OUT CP
RIPPLE_CP
Applications Information
is the output capacitor of the charge
_
______________________________________________________________________________________
is the load current of the charge
Charge-Pump Output Capacitor
= (V
≥
Charge-Pump Rectifier Diode
2
is the desired peak-to-peak
INL
f
OSC RIPPLE CP
or Power Dissipation
I
LOAD CP
- V
V
OUTL
_
) x I
_
OUTL
Low-Cost, Linear-Regulator
LCD Panel Power Supplies
The operational amplifier is typically used as the VCOM
buffer in TFT LCD panels. The output voltage of the
VCOM buffer can be adjusted using the MAX1512,
which is an EEPROM-programmable VCOM calibrator,
using the circuit shown in Figure 9. Refer to the
MAX1512 data sheet for details.
Figure 8. High-Power Linear Regulator
Figure 9. Using the MAX1512 to Adjust the V
CE
CTL
Using the MAX1512 VCOM Calibrator
MAX1512
REGULATOR
V
GND
DD
LINEAR
MAX8710
MAX8711
MAX8712
MAX8761
AV
OUT
SET
DD
100kΩ
20kΩ
to Adjust the Buffer Output
25kΩ
OUTL
FBL
INL
0.47µF
4.7µF
0.1µF
20kΩ
140kΩ
51Ω
REF
OUTL
SUPB
POSB
NEGB
V
IN
= 19V
KSB834W
(FAIRCHILD)
MAX8710
MAX8711
MAX8761
COM
4.7µF
4.7µF
Buffer Output
AVDD = 10V
OUTB
VCOM
TO
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