AIC1533 Просмотр технического описания (PDF) - Analog Intergrations

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производитель

AIC1533

Triple-Output LCD Power Supply

Analog Intergrations 

AIC1533

For negative charge pump, the number of negative

charge pump can be determined by

NNEG

≥

RTH × Iout − VNEG

Vcc − 2VD

(6)

where VNEG = output of negative charge pump

Example

To obtain VPOS=28V/30mA, VNEG=-9V/30mA from

VCC=12V, CFLY=0.1µF, the number of positive and

negative charge pumps can be calculated as

follows

RTH

=

2(R DS,ON(P )

+ RDS,ON(N) )

+

(

1

CFLY × FSW

)+(

CO

1

× FSW

)

= 2(10 + 10) + (

1

)+(

1

)

0.1× 10 −6 × 1× 106 1× 10 −6 × 1× 106

=51

(7)

NPOS

≥ VPOS − Vcc + R TH × Iout = 28 − 12 + (51× 30 × 10 −3 )

Vcc − 2VD

12 − 2 × 0.5

= 1.59

(8)

NNEG

≥ R TH × Iout − VNEG = (51× 30 × 10 −3 ) − (−9) (9)

Vcc − 2VD

12 − 2 × 0.5

= 0.96

Thus, the number of positive charge pump is two,

and the negative one requires one charge pump.

2. Output Voltage Selection

2.1 Output voltage of LDO

A resistor divider, determining output voltage of

LDO, connects to OUT, GND, and ADJ (referred to

TYPICAL APPLICATION CIRCUIT). Values of

resistors can be calculated by equation (10).

VLDO

=

VADJ

× (1+

R3 )

R4

(10)

where VLDO = output voltage of LDO

VADJ = adjustable voltage of LDO, the

recommended R4 is 130kΩ.

2.2. Output Voltage Of Positive Charge

Pump

Output voltage of positive charge pump is

determined by connecting a resistor divider to

output terminal of positive charge pump, GND, and

FBP (referred to TYPICAL APPLICATION

CIRCUIT). The values of resistor divider can be

calculated as equation (11).

VPOS

=

VFBP

× (1+

R1 )

R2

(11)

where VPOS = output voltage of positive charge

pump

VFBP = feedback voltage of positive charge pump,

1.25V. The recommended R2 is 22kΩ

2.3 Output voltage of negative charge

pump

Since comparator input of negative charge pump,

FBN, is referenced to 0V, a positive reference

voltage, which can be obtained by adding a 0.22µF

bypass capacitor between VREF and GND, is

needed (referred to TYPICAL APPLICATION

CIRCUIT). The value of resistor dividers can be

calculated as equation (12).

VNEG

=

−VREF

×

R5

R6

(12)

where VNEG represents output voltage of negative

charge pump, and VREF means reference voltage,

1.25V. The recommended R6 is 33kΩ.

13

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