MAX1542ETP+T Maxim Integrated Products, MAX1542ETP+T Datasheet - Page 17

• Manufacturer Part Number: MAX1542ETP+T
• Description: IC DC-DC CONV TFT-LCD 20-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1542ETP+T

• Applications: Controller, TFT, LCD
• Voltage - Input: 2.6 ~ 5.5 V
• Number Of Outputs: 2
• Voltage - Output: 2.6 ~ 13 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

negative charge-pump output voltages for a given
V
based on the following equations:
where G_ON is the positive charge-pump output volt-
age, G_OFF is the negative charge-pump output volt-
age, n is the number of charge-pump stages, and V
the voltage drop across each diode.
V
diodes.
Increasing the flying capacitor (C3, C4, and C5) value
increases the output current capability. Increasing the
capacitance indefinitely has a negligible effect on out-
put current capability because the internal switch resis-
tance and the diode impedance limit the source
impedance. 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
example, the two-stage positive charge pump in the
Typical Application Circuits (Figures 1 and 2) where
V
capacitor in the first stage (C5) requires a voltage rat-
Figure 5. Positive Charge-Pump Output Voltage vs. V
MAIN
D
MAIN
is the forward voltage drop of the charge-pump
for one-, two-, and three-stage charge pumps,
= 8V contains two flying capacitors. The flying
60
50
40
30
20
10
0
2
G ON
G OFF
V
2-STAGE CHARGE-PUMP
D
_
_
= 0.3V TO 1V
OUTPUT VOLTAGE vs. V
______________________________________________________________________________________
4
MAIN
POSITIVE CHARGE-PUMP
V
CX
=
= −
6
V
> n
is the main output voltage. For
MAIN
V
3-STAGE CHARGE-PUMP
1-STAGE CHARGE-PUMP
n V
MAIN
(
✕
8
MAIN
V
(V)
+
MAIN
n V
10
(
TFT LCD DC-to-DC Converter with
−
MAIN
MAIN
V
Flying Capacitors
D
12
)
−
V
14
D
)
MAIN
D
is
ing greater than 8V. The flying capacitor in the second
stage (C4) requires a voltage rating greater than 16V.
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 V
voltage ripple.
To maximize the available output voltage, use Schottky
diodes with a current rating equal to or greater than two
times the average charge-pump input current. If the
loaded charge-pump output voltage is greater than
required, some or all of the Schottky diodes can be
replaced with low-cost silicon switching diodes with an
equivalent current rating. The charge-pump input cur-
rent is:
where n is the number of charge-pump stages.
Figure 6. Negative Charge-Pump Output Voltage vs. V
Operational Amplifiers
RIPPLE
-10
-15
-20
-25
-30
-35
-40
-45
-0
-5
2
C
CHARGE-PUMP
is the acceptable peak-to-peak output-
OUT
V
D
I
CP IN
CHARGE-PUMP
= 0.3V TO 1V
OUTPUT VOLTAGE vs. V
2-STAGE
NEGATIVE CHARGE-PUMP
4
_
≥
Charge-Pump Output Capacitor
3-STAGE
2
Charge-Pump Rectifier Diodes
=
6
×
F
I
CP OUT
V
OSC
MAIN
I
_
LOAD
8
(V)
×
V
10
RIPPLE
1-STAGE
CHARGE-PUMP
×
n
MAIN
12
14
MAIN
17