AS1320 查看數據表（PDF） - austriamicrosystems AG

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AS1320

200mA Step-Up DC-DC Converter

austriamicrosystems AG 

AS1320

Data Sheet - Application Information

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

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

Where:

RIND is the inductor series resistance.

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

(EQ 2)

(EQ 3)

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:

Where:

r is the desired output ripple in %.

COUT > (L + 2.5µH) x VBATT(MAX)2/ r%

(EQ 4)

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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