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AS1335

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

Higher value, low cost ceramic capacitors are available in very small case sizes, and their high ripple current, high volt-

age rating, and low ESR make them ideal for switching regulator applications. Because the AS1335 control loop is not

dependant on the output capacitor ESR for stable operation, ceramic capacitors can be used to achieve very low out-

put 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 power-

save mode and tighten DC output accuracy in powersave mode.

Input Capacitor Selection

voltage transients while minimizing the interference with other circuits caused by high input voltage spikes, a low ESR

input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given as:

for design because even significant deviations only provide negligible affects.

The input capacitor can be increased without any limit for better input voltage filtering. Take care when using small

ceramic input capacitors. When a small ceramic capacitor is used at the input, and the power is being supplied through

pin. This ringing can then couple to the output and be mistaken as loop instability, or could even damage the part by

exceeding the maximum ratings.

Ceramic Input and Output Capacitors

These dielectrics have the best temperature and voltage characteristics for a given value and size. Y5V and Z5U

dielectric capacitors, aside from their wide variation in capacitance over temperature, become resistive at high frequen-

cies and therefore should not be used.

Because ceramic capacitors lose a lot of their initial capacitance at their maximum rated voltage, it is recommended

that either a higher input capacity or a capacitance with a higher rated voltage is used.

Table 4. Recommended External Components

Name

Part Number

Value

Rating

Type

Size

Manufacturer

T520B107M006ATE040

100µF

6.3V

Tantal

B

(3.5x2.8x1.9mm)

Kemet

www.kemet.com

GRM21BR60J226ME39

22µF

6.3V

X5R

0805

Murata

www.murata.com

L

MOS6020-222ML

2.2µH

3.26A

35m

Ω

6.8x6.0x2.4mm

Coilcraft

www.coilcraft.com

MOS6020-472ML

4.7µH

1.82A

50m

Ω

6.8x6.0x2.4mm

(EQ 4)

ΔV

OUT

V

OUT

1

V

OUT

V

IN

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

–

Lf

×

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

1

8

C

OUT

×

f

×

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

ESR

+

⎝⎠

⎛⎞

×

×

=

(EQ 5)

I

RMS

I

MAX

V

OUT

V

IN

V

OUT

–

()

×

V

IN

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

×

=