MAX8740 Maxim Integrated Products, MAX8740 Datasheet - Page 5

• Manufacturer Part Number: MAX8740
• Description: TFT-LCD Step-Up DC-DC Converter
• Manufacturer: Maxim Integrated Products

Figure 1. Typical Operating Circuit
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PIN
4, 5
6, 7
10
1
2
3
8
9
4.5V TO 5.5V
NAME
COMP
SHDN
FREQ
GND
FB
LX
SS
IN
V
IN
10µF
6.3V
_______________________________________________________________________________________
C1
Compensation Pin for Error Amplifier. Connect a series RC from COMP to ground. See the Loop
Compensation section for component selection guidelines.
Feedback Pin. The FB regulation voltage is 1.24V nominal. Connect an external resistive voltage-divider
between the step-up regulator’s output (V
divider close to the IC and minimize the trace area to reduce noise coupling. Set V
Output Voltage Selection section.
Shutdown Control Input. Drive SHDN low to turn off the MAX8740.
Ground. Connect pins 4 and 5 directly together.
Switch Pin. LX is the drain of the internal MOSFET. Connect the inductor/rectifier diode junction to LX and
minimize the trace area for lower EMI. Connect pins 6 and 7 directly together.
Supply Pin. Bypass IN with a minimum 1µF ceramic capacitor directly to GND.
Frequency-Select Input. When FREQ is low, the oscillator frequency is set to 640kHz. When FREQ is high, the
frequency is 1.2MHz. This input has a 5µA pulldown current.
Soft-Start Control Pin. Connect a soft-start capacitor (C
start capacitor is charged with a constant current of 4.5µA. Full current limit is reached after t = 2.5 x 10
The soft-start capacitor is discharged to ground when SHDN is low. When SHDN goes high, the soft-start
capacitor is charged to 0.4V, after which soft-start begins.
1µF
10Ω
C3
R3
33nF
C6
TFT-LCD Step-Up DC-DC Converter
10
8
9
3
IN
FREQ
SHDN
SS
2.7µH
L1
LX
6
MAX8740
LX
COMP
7
GND
GND
D1
FB
OUT
2
5
4
1
) and GND, with the center tap connected to FB. Place the
R4
47kΩ
1%
C4
560pF
FUNCTION
R1
196kΩ
1%
R2
20kΩ
1%
SS
) to this pin. Leave open for no soft-start. The soft-
C5
68pF
C2
10µF
20V
C7
10µF
20V
OUT
Pin Description
according to the
V
13.5V/800mA
OUT
5
C
SS
.
5