CS5332 datasheet(17/20 Pages) ONSEMI

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CS5332

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RV(DRP) + DVDRP

RV(FB) DVOUT

Calculate Input Filter Capacitor Current Ripple

The procedure below assumes that phases do not overlap

and output inductor ripple current (P−P) is less than the

average output current of one phase.

9. Calculate Input Current

IIN +

VOUT

IOUT

(Efficiency

VIN)

10. Calculate Duty Cycle (per phase).

Duty Cycle +

VOUT

(Efficiency

VIN)

11. Calculate Apparent Duty Cycle.

Apparent Duty Cycle + Duty Cycle

#of Phases

12. Calculate Input Filter Capacitor Ripple Current. Use

the chart in Figure 17 to calculate the normalized

ripple current (KRMS) based on the reciprocal of

Apparent Duty Cycle. Then multiply the input current

by KRMS to obtain the Input Filter Capacitor Ripple

Current.

Ripple (RMS) + IIN

KRMS

4.00

3.50

3.00

2.50

2.00

1.50

1.00

0.50

0.00

1/ Apparent Duty Cycle

Figure 17. Normalized Input Filter Capacitor

Ripple Current

DESIGN EXAMPLE

Choose the component values for a 240 kHz, 12 V to 1.525

V, 41 A converter with lossless current sensing, adaptive

positioning and a 50 A current limit. The adaptive

positioning is chosen 50 mV below the DAC setting at no

load and 50 mV below the no−load position with 41 A out.

The peak output voltage transient is 70 mV max during a 41

A step current.

Current Sensing, Power Stage and

Output Filter Components

1.Assume 1.5 mΩ of output filter ESR.

+ (VIN * VOUT)

(VOUT VIN) (F

25 mV)

+ (12 * 1.55)

(1.55 12) (240 k

.01mF

25mV)

+ 22.5 k

L RL + .01 mF

22.5 kW + 225 ms

Choose RL + 2.0 mW

L + 2.0 mW

225 ms + 450 nH

3. n/a

PwrstgZ + RL

CSA Gain 2.0

+ 2.0 mW

3.15 2 + 3.1 mW

ConverterZ

PwrstgZ

ESR

PwrstgZ ) ESR

+ 3.1 mW

1.5 mW

3.1 mW ) 1.5 mW

^ 1.0 mW

DVR + 1.0 mW

41 A + 41 mV

5. n/a

Current Limit

VI(LIM) + RL

IOUT(LIM)

CS to ILIM Gain

+ 2.0 mW

50 A

6.25 + 625 mV

Adaptive Positioning

RV(FB) + NL Position VFB Bias Current

+ 50 mV 18 mA + 2.78 kW

DVDRP + RL

IOUT

Current Sense to VDRP Gain

+ 2.0 mW

41 A

3.1 + 254 mV

RV(DRP) + DVDRP

RV(FB) DVOUT

+ 254 mV

2.78 kW 50 mV + 25.4 kW

IIN + 1.52 V

41 A

(0.85

12VIN)

+ 6.1 A

Duty Cycle +

1.52 V

(0.85

12 VIN)

+ 0.15

10.

Apparent Duty Cycle + 0.15

2.0 + 0.3

11.

RMS ripple is 6.1 A

1.5 + 9.2 A

12.

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