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AS1324

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

9.3 Output Capacitor Selection

The advanced fast-response voltage mode control scheme of the AS1324 allows the use of tiny ceramic capacitors. Because of their lowest

output voltage ripple low ESR ceramic capacitors are recommended. X7R or X5R dielectric output capacitor are recommended.

At high load currents, the device operates in PWM mode and the RMS ripple current is calculated as:

While operating in PWM mode the overall output voltage ripple is the sum of the voltage spike caused by the output capacitor ESR plus the

voltage ripple caused by charging and discharging the output capacitor:

Higher value, low cost ceramic capacitors are available in very small case sizes, and their high ripple current, high voltage rating, and low ESR

make them ideal for switching regulator applications. Because the AS1324 control loop is not dependant on the output capacitor ESR for stable

operation, ceramic capacitors can be used to achieve very low output ripple and accommodate small circuit size.

At light loads, the converter operates in powersave mode and the output voltage ripple is in direct relation to the output capacitor and inductor

value used. Larger output capacitor and inductor values minimize the voltage ripple in powersave mode and tighten DC output accuracy in

powersave mode.

Table 5. Recommended Inductors

Part Number

L

DCR

Current Rating

Dimensions (L/W/T)

Manufacturer

LQH32CN2R2M33

2.2µH

97m

Ω

790mA

3.2x2.5x2.0mm

Murata

www.murata.com

LQH32CN4R7M33

4.7µH

150m

Ω

650mA

3.2x2.5x2.0mm

LPS3008-222MLC

2.2µH

175m

Ω

1100mA

3.1x3.1x0.8mm

Coilcraft

www.coilcraft.com

LPS3015-222MLC

2.2µH

110m

Ω

2000mA

3.1x3.1x1.5mm

MOS6020-222MLC

2.2µH

35m

Ω

3260mA

6.0x6.8x2.4mm

MOS6020-472MLC

4.7µH

50m

Ω

1820mA

6.0x6.8x2.4mm

CDRH3D16NP-2R2N

2.2µH

72m

Ω

1200mA

4.0x4.0x1.8mm

Sumida

www.sumida.com

CDRH3D16ND-4R7N

4.7µH

105m

Ω

900mA

4.0x4.0x1.8mm

70

75

80

85

90

95

1

10

100

1000

Output Current (mA)

LQH32CN2R2

LPS3008-222

LPS3015-222

M OS6020-222

LQH32CN4R7

M OS6020-472

70

75

80

85

90

95

1

10

100

1000

Output Current (mA)

LQH32CN2R2

LPS3008-222

LPS3015-222

M OS6020-222

LQH32CN4R7

M OS6020-472

(EQ 4)

I

RMSC

OUT

V

OUT

1

V

OUT

V

IN

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

–

L

f

×

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

1

2

3

×

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

×

×

=

(EQ 5)

∆V

OUT

V

OUT

1

V

OUT

V

IN

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

–

L

f

×

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

1

8

C

OUT

×

f

×

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

ESR

+









×

×

=