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Data Sheet

ADP5053

Rev. B | Page 29 of 36

SELECTING THEOUTPUT CAPACITOR

The output capacitor must meet the output voltage ripple and

load transient requirements. To meet the output voltage ripple

requirement, use the following equations to calculate the ESR

and capacitance:

RIPPLE

OUT

RIPPLE

OUT

∆

RIPPLE

OUT

ESR

∆

The calculated capacitance, COUT_RIPPLE, is 20.8 µF, and the

calculated RESR is 10 mΩ.

To meet the ±5% overshoot and undershoot requirements, use

the following equations to calculate the capacitance:

(

)

OUT

STEP

OUT

∆

−

∆

(

)

OUT

OUT_OV

OUT

STEP

OUT

−

∆

For estimation purposes, use KOV = KUV = 2; therefore, COUT_OV =

117 µF and COUT_UV = 13.3 µF.

The ESR of the output capacitor must be less than13.3mΩ,and the

output capacitance must be greater than 117µF. Itis recommended

that three ceramic capacitors be used (47 µF,X5R, 6.3V), such as

the GRM21BR60J476ME15 from Murata with an ESR of 2 mΩ.

SELECTING THELOW-SIDEMOSFET

A low RDSON N-channel MOSFET must be selected for high

efficiency solutions. The MOSFET breakdown voltage (VDS)

must be greater than 1.2 × VIN, and the drain current must be

greater than 1.2 × ILIMIT_MAX.

It is recommended that a 20 V, dual N-channel MOSFET, such

as the Si7232DN from Vishay, be used for both Channel 1 and

Channel 2. The RDSON of the Si7232DN at 4.5 V driver voltage is

16.4 mΩ, and the total gate charge is 12 nC.

DESIGNING THECOMPENSATION NETWORK

For better load transient and stability performance, set the cross

frequency, fC, to fSW/10. In this example, fSW is set to 600 kHz;

therefore, fC is set to 60 kHz.

For the 1.2 V output rail, the 47 µF ceramic output capacitor has

a derated value of 40 µF.

kΩ

14.4

A/V

470

0.8

kHz

1.2

(

)

2.51

kΩ

14.4

μF

0.001

0.3

8.3

kΩ

14.4

μF

0.001

Choose standard components: RC = 15 kΩ and CC = 2.7 nF.

CCP is optional.

Figure 48 shows the Bode plot for the 1.2 V output rail. The

cross frequency is 62 kHz,and thephase marginis 58°.Figure49

shows the load transient waveform.

100

–100

–80

–60

–40

–20

120

–180

–150

–120

–90

–60

–30

10k

100k

FREQUENCY (Hz)

CROSS FREQUENCY: 62kHz

PHASE MARGIN: 58°

Figure 48. Bode Plot for 1.2 V Output

CH1 50.0mV

CH4 2.00A Ω BW

M200µs

A CH4

2.32A

VOUT

IOUT

Figure 49. 0.8 A to 3.2 A Load Transient for 1.2 V Output

SELECTING THESOFT START TIME

The soft start feature allows the output voltage to ramp up in a

controlled manner, eliminating output voltage overshoot during

soft start and limiting the inrush current.

Use the SS12 pin to program a soft start time of 2 ms, 4 ms,

or 8 ms and to configure parallel operationof Channel 1 and

Channel 2. For more information, see the Soft Start section

and Table 9.

SELECTING THEINPUT CAPACITOR

For the input capacitor, selecta ceramic capacitor with a minimum

value of 10 µF; place the input capacitor near to the PVIN1 pin.

In this example, one 10 µF, X5R, 25 V ceramic capacitor is

recommended.

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