AIC1533 Ver la hoja de datos (PDF) - Analog Intergrations

Número de pieza

componentes Descripción

Fabricante

AIC1533

Triple-Output LCD Power Supply

Analog Intergrations 

AIC1533

T2 = Cp × VTH,P

(2)

IP

where VTH,P = positive threshold voltage, 1.25V

IP= positive bias current, 5µA

Current Limit And Thermal Protection

To protect devices from damage caused by short

circuit, AIC1533 provides current limit and thermal

protection. When short circuit occurs, output current

is clamped at the current limit. Due to power

dissipation of LDO is defined as

PDISSIPATION = IOUT * (VIN-VOUT)

(3)

Under short circuit condition, the temperature rising,

which is caused by power dissipation, gets to

thermal shutdown temperature and shuts AIC1533

down. As the temperature gets lower than the

thermal shutdown temperature, the device will

resume. The pattern of temperature of the device

recycles until the short circuit condition is removed.

The waveform under short circuit condition is shown

as Fig.18.

IOUT

Current

Limit

Thermal Shutdown

VOUT

Fig.18 Current Limit Waveform of AIC1533

Shutdown

AIC1533 shuts off all devices and consumes only

0.1µA supple current when SHDN gets lower than

0.6V. This pin can be pulled high to 2.4V for normal

operation. Due to high impedance of SHDN pin, it

can’t be floating.

Components Selection

1. Determining The Number Of Charge

Pump Stages

The number of charge pump stages to regulate is

determined by output voltage, supply voltage,

switching frequency, load current, forward voltage

of diodes, on-resistor of internal MOSFET, and

value of ceramic capacitor.

For positive charge pump, the number of required

stages can be calculated as

NPOS

≥

VPOS

− Vcc + RTH

Vcc − 2VD

× Iout

(4)

where VPOS = output of positive charge pump

RTH = equivalent output impedance of

charge pump

VD = forward voltage of diodes

Vcc = input voltage

The following equation approximates RTH

RTH =

2(R DS,ON(P )

+ RDS,ON(N) )

+( 1 )+( 1

CFLY × FSW CO × FSW

)

(5)

where RDS, ON(P) is on-resistor of internal P-channel

MOSFET, RDS, ON(N) means on-resistor of internal

N-channel MOSFET, and FSW is switching

frequency of AIC1533 (referring to ELECTRIVAL

CHARACTERISTICS).

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