Rainbow-electronics MAX1621 Manual de usuario descargar pdf (Pagina 11)

MAX1620/MAX1621

Digitally Adjustable LCD Bias Supplies

______________________________________________________________________________________ 11

maximum switching frequency. The following equation

represents the output current for the ideal case (no

power losses) of Figure 5:

This means that a higher peak current is required to

achieve the same output current in the negative output

circuit as in the positive output circuit.

The output current for Figure 6 uses the same current

equation as the positive boost.

Output Voltage Control

The output voltage is set with a voltage divider to the

feedback pin (FB). For a positive output, the divider is

referred to GND; for a negative output, the divider is

referred to REF.

Output voltage can be adjusted with an internal DAC

summing current into FB through an external resistor.

The 5-bit DAC is controlled with a user-programmable

up/down counter. On power-up or after a reset, the

counter sets the DAC output to 10000 binary, or half-

scale.

I x (k-factor / L) x V / (V V )

OUT BATT BATT OUT

15V

BATT

POK

MMFT3055VL

POL

SHDN (SUS)

DN (SDA)

UP (SCL)

REF

AGND

( ) ARE FOR MAX1621.

NOTE: CONNECTIONS TO DIGITAL INPUTS NOT SHOWN.

300k

1.2M

100pF

DHI

DLO

PGND

DOUT

LCDON

5.5V

0.1µF

22µF

-6V

-12V OUT

100µH

MBRS0540

1µF

MAX1620

MAX1621

10k

TO REF

D3 1N6263 (ANY SCHOTTKY)

12V

BATT

POK

MMFT3055VL

POL

SHDN (SUS)

DN (SDA)

UP (SCL)

REF

AGND

( ) ARE FOR MAX1621.

NOTE: CONNECTIONS TO DIGITAL INPUTS NOT SHOWN.

300k

2.7M

100pF

DHI

DLO

PGND

DOUT

LCDON

5.5V

0.1µF

22µF

-13.5V

-27V OUT

100µH

MBRS0540

2.2µF

MAX1620

MAX1621

10k

TO REF

D3 1N6263 (ANY SCHOTTKY)

Figure 5. Typical Operating Circuit—Negative Output

Figure 6. Alternative Negative Output—Maximum Voltage

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 19 20

MAX1620/MAX1621 1

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Rainbow-electronics MAX1621 Manual de usuario Pagina 11

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