ADP5050ACPZ-R7 datasheet(35/60 Pages) AD

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Data Sheet

ADP5050

Rev. 0 | Page 35 of 60

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:

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 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 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 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 40 µF.

Ω

A/V

470

kHz

(

)

001

Ω

001

Ω

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

CCP is optional.

Figure 62 shows the Bode plot for the 1.2 V output rail.

The cross frequency is 62 kHz, and the phase margin is 58°.

Figure 63 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 62. Bode Plot for 1.2 V Output

CH1 50.0mV

CH4 2.00A Ω BW

M200µs

A CH4

2.32A

VOUT

IOUT

Figure 63. 0.8 A to 3.2 A Load Transient 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 SS12 pin can be used to program a soft start time of 2 ms,

4 ms, or 8 ms and can also be used to configure parallel opera-

tion of Channel 1 and Channel 2. For more information, see the

Soft Start section and Table 10.

SELECTING THE INPUT CAPACITOR

For the input capacitor, select a ceramic capacitor with a mini-

mum value of 10 µF; place the input capacitor close to the PVIN1

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

recommended.

ADP5050ACPZ-R7 Datasheet(PDF) 35 Page - Analog Devices

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