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ADP5054

Data Sheet

Rev. B | Page 26 of 31

SELECTING THE OUTPUT 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:

OUT_RIPPLE

∆

OUT_RIPPLE

ESR

∆

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

calculated ESR, 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 than 13.3 mΩ,

and the output capacitance must be greater than 117 µF. It is

recommended that three ceramic capacitors be used (47 µF,

X5R, 6.3 V), such as the GRM21BR60J476ME15 from Murata

with an ESR of 2 mΩ.

SELECTING THE LOW-SIDE MOSFET

A low RDS(ON) N-channel MOSFET must be selected for high

efficiency solutions. The MOSFET breakdown voltage must be

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

than 1.2 × ILIMIT.

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

as the Si4204DY from Vishay) be used for both Channel 1 and

Channel 2. The RDS(ON) of the Si4204DY at a 4.5 V driver voltage

is 6 mΩ, and the total gate charge is 14.5 nC.

DESIGNING THE COMPENSATION 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 32 µF.

kΩ

A/V

μs

470

kHz

μF

(

)

kΩ

μF

001

kΩ

μF

001

Choose standard components: RC = 5.6 kΩ and CC = 4.7 nF.

CCP is optional.

Figure 40 shows the bode plot for the 1.2 V output rail. The

cross frequency is 64 kHz, and the phase margin is 65°.

Figure 41 shows the load transient waveform.

–120

–100

–80

–60

–40

–20

100

120

–120

–100

–80

–60

–40

–20

100

120

10k

100k

FREQUENCY (Hz)

CROSS FREQUENCY: 64kHz

PHASE MARGIN: 65°

Figure 40. Bode Plot for 1.2 V Output

Figure 41. 0.8 A to 3.2 A Load Transient Waveform for 1.2 V Output

SELECTING THE SOFT 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.

The CFG12 pin can be used to program a soft start time of 2 ms

or 16 ms and can also be used to configure parallel operation of

Channel 1 and Channel 2. For more information, see the Soft

Start section and Table 8.

SELECTING THE INPUT CAPACITOR

For the input capacitor, select a ceramic capacitor with a

minimum value of 10 µF; place the input capacitor close to the

PVINx pin. In this example, one ceramic capacitor of 10 µF,

X5R, 25 V is recommended.

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