AS1344 datasheet(12/19 Pages) AMSCO

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AS1344

Datasheet - A p p l i c a t i o n I n f o r m a t i o n

Thermal Protection

To protect the device from short circuit or excessive power dissipation of the auxiliary NPNs, the integrated thermal

protection switches off the device when the junction temperature (TJ) reaches 140ºC (typ). When TJ decreases to

approximately 135ºC, the device will resume normal operation. If the thermal overload condition is not corrected, the

device will switch on and off while maintaining TJ within the range between 135 and 140ºC.

Setting Output Voltage

Output voltage can be adjusted by connecting a voltage divider between pins

VOUT and FB (see Figure 35).

Figure 35. Typical Application

The output voltage can adjusted by selecting different values for R1 and R2. For R2, select a value between 10k and

200k

Ω.

Calculate R1 by:

Where:

VOUT = 5.5V to 42V, VFB = 1.25V; VOUT > VIN

The input bias current of FB has a maximum value of 100nA which allows for large-value resistors. For less than 1%

error, the current through R2 should be 100 times the feedback input bias current (IFB). That’s why the feeback current

can be neglected in the calculation of VOUT.

Note:

For the optimal operation condition the following ratio between VOUT and VIN should be used:

GND

VCC

Off

2.2M

VOUT = 18V

AS1344

6.8µH

10µF

VCC = 0.9V

to 3.6V

COUT

4.7µF

165k

SWOUT

PGND

VOUT

POK

100k

VIN

(EQ 2)

VOUT

VFB

--------------

–

⎝⎠

⎛⎞

⋅

(EQ 3)

VOUT

VIN

≤

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