Rainbow Electronics MAX8727 - Manual (Page 6)

MAX8727
TFT-LCD Step-Up DC-DC Converter
6 _______________________________________________________________________________________
PIN NAME FUNCTION
1 COMP
Compensation Pin for Error Amplifier. Connect a series RC from COMP to ground. See the Loop
Compensation section for component selection guidelines.
2 FB
Feedback Pin. The FB regulation voltage is 1.24V nominal. Connect an external resistive voltage-divider
between the step-up regulator’s output (V
OUT ) and GND, with the center tap connected to FB. Place the
divider close to the IC and minimize the trace area to reduce noise coupling. Set V OUT according to the
Output Voltage Selection section.
3 SHDN Shutdown Control Input. Drive SHDN low to turn off the MAX8727.
4 GND Ground. Connect pins 4 and 5 directly together.
5 GND Ground. Connect pins 4 and 5 directly together.
6 LX
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.
7 LX
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.
8 IN Supply Pin. Bypass IN with a minimum 1µF ceramic capacitor directly to GND.
9 FREQ
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.
10 SS
Soft-Start Control Pin. Connect a soft-start capacitor (C SS ) to this pin. Leave open for no soft-start. The soft-
start capacitor is charged with a constant current of 4.5µA. Full current limit is reached after t = 2.5 × 10 5 C SS .
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.
Pin Description
LX LX
FB
GND
GND
FREQ
IN
COMP SS
1
4
5
2
3
9
8
6 7
10
V
OUT
15V/600mA
V IN
4.5V TO 5.5V
SHDN
MAX8727
C1
10 µF
6.3V
R3
10 Ω
C3
1 µF
C6
33nF
C4
330pF
C5
39pF
L1
3.6 µH D1
R2
28.0k
Ω
1%
R4
100k
Ω
R1
309k
Ω
1%
C2
4.7
µF
25V
C7
4.7
µF
25V
C8
4.7
µF
25V
Figure 1 Typical Operating Circuit