AS1320 datasheet(9/12 Pages) AMSCO

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AS1320

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

9 Application Information

Inductor Selection

The control circuitry of the AS1320 permits a wide range of inductor values to be selected – from 4.7 to 47µH; 10µH is

ideal for most applications.

The intended application should dictate the value of L. The trade-off between required PCB surface area and desired

output ripple are the determining factors: smaller values for L require less PCB space, larger values of L reduce output

ripple. If the value of L is large enough to prevent IMAX from being reached before tON expires, the AS1320 output

power will be reduced.

For maximum output current calculate the value for L as:

(VBATT(MAX) (1µs))/0.7A < L < (VBATT(MIN)(7µs))/0.7A

(EQ 2)

IOUT(MAX) = [(0.7A/2)(VBATT(MIN) - (0.7A/2)(RNCH + RIND))]/VOUT

(EQ 3)

Where:

RIND is the inductor series resistance.

RNCH is the RDS(ON) of the N-channel MOSFET (0.3

Ω typ).

Note: Coils should be able to handle 500mARMS and have a ISAT

≥ 1A and should have a RIND ≤ 100mΩ.

Capacitor Selection

COUT Selection

Choose a COUT value to achieve the desired output ripple percentage. A 22µF ceramic capacitor is a good initial value.

The value for COUT can be determined by:

COUT > (L + 2.5µH) x VBATT(MAX)

/ r%

(EQ 4)

Where:

r is the desired output ripple in %.

CIN Selection

CIN reduces the peak current drawn from the battery and can be the same value as COUT. A larger value for CIN can be

used to further reduce ripple and improve AS1320 efficiency.

PC Board Layout and Grounding

Well-designed printed circuit-board layout is important for minimizing ground bounce and noise.

Place pin GND lead and the ground leads of CIN and COUT as close to the device as possible.

Keep the lead to pin LX as short as possible.

To maximize output power and efficiency and minimize output ripple voltage, use a ground plane and solder the

GND pin directly to the ground plane.

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