CS5323

http://onsemi.com

15

4.00

3.50

3.00

2.50

2.00

1.50

1.00

0.50

0.00

1/ Apparent Duty Cycle

15

10

5

0

Figure 13. Normalized Input Filter Capacitor

Ripple Current

DESIGN EXAMPLE

Choose the component values for lossless current sensing,

adaptive positioning and current limit for a 12 V to 1.5 V 60

A converter. The adaptive positioning is chosen 20 mV

no–load position with 60 A out. The peak output voltage

transient is 100 mV max during a 60 A step current. The

overcurrent limit is nominally 75 A.

Current Sensing, Power Stage

and Output Filter Components

1. Assume 1.5 m

Ω of output filter ESR.

R

+ (VIN * VOUT)

(VOUT VIN) (F

C

25 mV)

+ (12 * 1.5)

(1.5 12) (250 k

.01

mF

25 mV)

+ 21 kW å Choose 20 kW

L RL + .01 mF

20 k

W + 200 ms

Choose RL + 2.0 mW

L

+ 2mW

200

ms + 400 nH

2

.

3. n/a

PwrstgZ

+ RL

CSA Gain 3

+ 1.5 mW

4.2 3

+ 2.1 mW

ConverterZ

+

PwrstgZ

ESR

PwrstgZ

) ESR

+ 2.8 mW

1.5 m

W

2.8 m

W ) 1.5 mW

^ 1.0 mW

DVR + 1.0 mW

60 A

+ 60 mV

4.

5. n/a

Current Limit

VI(LIM) + RL

IOUT(LIM)

CS to ILIM Gain

+ 1.5 mW

75 A

6.5

+ 731 mV

6.

Adaptive Positioning

RV(FB) + NL Position VFB Bias Current

+ 20 mV 19 mA ^ 1.00 kW

7.

DVDRP + RL

IOUT

Current Sense to VDRP Gain

+ 2mW

60 A

3

+ 360 mV

RV(DRP) + DVDRP

RV(FB) DVOUT

+ 360 mV

1.00 k

W 50 mV + 7.2 kW

8.

IIN +

1.6 V

60 A

(0.85

12VIN)

+ 9.4 A

9.

Duty Cycle

+

1.6 V

(0.85

12 VIN)

+ 0.16

10.

Apparent Duty Cycle

+ 0.16

3.0

+ 0.48

11.

RMS ripple is 9.4 A

1.0

+ 9.4 A

12.