MAX8795AGCJ/V+T Maxim Integrated Products, MAX8795AGCJ/V+T Datasheet - Page 22

• Manufacturer Part Number: MAX8795AGCJ/V+T
• Description: Display Drivers TFT-LCD DC-DC Conver ter with Operational
• Manufacturer: Maxim Integrated Products

Specifications of MAX8795AGCJ/V+T

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The number of positive charge-pump stages is given by:
where n
stages, V
put, V
TFT-LCD DC-DC Converter with
Operational Amplifiers
Figure 8. Positive Charge-Pump Output Voltage vs. V
Figure 9. Negative Charge-Pump Output Voltage vs. V
22
______________________________________________________________________________________
MAIN
POS
GON
n
60
50
40
30
20
10
POS
is the main step-up regulator output, V
-10
-15
-20
-25
-30
-35
-40
-45
0
-0
-5
is the number of positive charge-pump
is the gate-on linear-regulator REG P out-
2
2
V
2-STAGE CHARGE PUMP
D
CHARGE PUMP
=
V
= 0.3V TO 1V
D
V
OUTPUT VOLTAGE vs. V
CHARGE PUMP
= 0.3V TO 1V
OUTPUT VOLTAGE vs. V
GON
4
2-STAGE
NEGATIVE CHARGE-PUMP
POSITIVE CHARGE-PUMP
4
3-STAGE
+
6
V
6
MAIN
V
V
3-STAGE CHARGE PUMP
DROPOUT
1-STAGE CHARGE PUMP
V
MAIN
MAIN
8
8
(V)
− ×
(V)
2
10
10
1-STAGE
CHARGE PUMP
V
D
MAIN
−
MAIN
V
12
12
MAIN
14
14
MAIN
MAIN
D
is
the forward-voltage drop of the charge-pump diode,
and V
ulator. Use V
The number of negative charge-pump stages is given by:
where n
stages, V
output, V
is the forward-voltage drop of the charge-pump diode,
and V
ulator. Use V
The above equations are derived based on the
assumption that the first stage of the positive charge
pump is connected to V
negative charge pump is connected to ground.
Sometimes fractional stages are more desirable for bet-
ter efficiency. This can be done by connecting the first
stage to V
charge-pump stage is powered from V
equations become:
Increasing the flying-capacitor (C
effective source impedance and increases the output-
current capability. Increasing the capacitance indefinitely
has a negligible effect on output-current capability
because the internal switch resistance and the diode
impedance place a lower limit on the source imped-
ance. A 0.1μF ceramic capacitor works well in most
low-current applications. The flying capacitor’s voltage
rating must exceed the following:
where n is the stage number in which the flying capaci-
tor appears, and V
main step-up regulator.
DROPOUT
DROPOUT
NEG
MAIN
GOFF
n
n
IN
POS
NEG
DROPOUT
DROPOUT
n
is the number of negative charge-pump
or another available supply. If the first
NEG
is the main step-up regulator output, V
is the dropout margin for the linear reg-
is the dropout margin for the linear reg-
is the gate-off linear-regulator REG N
=
=
V
−
=
GON
V
V
MAIN
GOFF
−
CX
V
= 0.3V.
= 0.3V.
V
GOFF
MAIN
V
MAIN
+
V
> ×
MAIN
MAIN
n V
V
is the output voltage of the
+
DROPOUT
V
+
DROPOUT
− ×
and the first stage of the
MAIN
− ×
− ×
V
2
DROPOUT
2
2
V
X
D
V
V
) value lowers the
Flying Capacitors
D
D
+
V
+
IN
IN
V
IN
, the above
D