MAX768 데이터 시트보기 (PDF) - Maxim Integrated

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MAX768

Low-Noise, Dual-Output, Regulated Charge Pump for GaAsFET, LCD, and VCO Supplies

Maxim Integrated 

Low-Noise, Dual-Output, Regulated Charge Pump

for GaAsFET, LCD, and VCO Supplies

Table 1. Shutdown-Control Logic

PSHDN

1

1

0

0

NSHDN

1

0

1

0

POUT

STATUS

Positive output active

Positive output active

Positive output inactive

Shutdown (low-power mode)

NOUT

STATUS

Negative output active

Negative output inactive

Negative output active

Shutdown (low-power mode)

Table 2. Charge-Pump Capacitor Selection (Figure 2)

SYNC

INPUT

GND

IN

External Clock

FREQUENCY

(kHz)

25

100

20 to 240

C1, C2, C3, C4

10µF

2.2µF

C = 220µF/f (kHz)

CAPACITORS

C5, C6

10µF

SUPPLY

CURRENT

(mA)

0.8

0.7

0.3

0.0001

C7

4.7µF

Shutdown

The MAX768 has two active-low, TTL logic-level shut-

down inputs: PSHDN and NSHDN. When both inputs

are pulled low, the MAX768 shuts down and the supply

current is reduced to 10µA max over temperature.

Pulling PSHDN low turns off the positive linear regula-

tor; the doubler charge pump remains active. Pulling

the NSHDN input low while PSHDN remains high turns

off the inverter charge pump, the negative linear regula-

tor, and the output-ready indicator (Table 1).

Capacitors

The overall dropout voltage is a function of the charge

pump’s output resistance and the voltage drop across

the linear regulator. The charge-pump output resistance

is a function of the switching frequency and the capaci-

tor’s ESR value. Therefore, minimizing the charge-pump

capacitors’ ESR minimizes dropout voltage.

( ) ( ) RPOUT = 84 + 8 C1ESR

+

C3ESR

+

2

fOSCC1

( ) ( ) RNOUT = 84 + 8 C1ESR + 4 C2ESR +

(C4ESR) +

2

fOSCC1

+

1

fOSCC2

VIN

C2

C4

C1-

C2+

GND

IN

C2-

C1+

V-

V+

MAX768

NOUT

POUT

SETN

SETP

NSHDN

RDY

PSHDN

SYNC

C1

C7

C3

+5V

C5

TO

VIN

C6

-5V

See Table 2 for capacitor selection. All capacitors

should be either surface-mount ceramic chip or tanta-

lum. External capacitor values may be adjusted to opti-

mize size, performance, and cost.

SEE TABLE 2 FOR CAPACITOR VALUES

Figure 2. MAX768 Standard Application Circuit

8 _______________________________________________________________________________________

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