ADDC02808PBTV(Rev0) Просмотр технического описания (PDF) - Analog Devices

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ADDC02808PBTV
(Rev.:Rev0)

28 V, 200 W Pulsed DC/DC Converter with Integral EMI Filter

Analog Devices 

ADDC02808PB

250

200

100W ave

150

MAXIMUM PEAK

POWER LIMIT

10W ave

50W ave

100

MAXIMUM CONTINUOUS

POWER LIMIT

50

8.1

8

7.9

7.8

12A STEP CHANGE

7.7

24A STEP CHANGE

7.6

7.5

7.4

0

–200 –100 0 100 200 300 400 500 600 700 800

OBSOLETE 0

25

50

75

100

125

150

PULSE WIDTH – ms

Figure 17. Largest On-State Power vs. Pulse Width that

Maintains TJMAX ≤ 110°C at 90°C Baseplate

TRANSIENT RESPONSE

The standard ADDC02808PB is designed to deliver large

changes, or pulses, in load current with minimum output

voltage deviation and an ultrafast return to the nominal output

voltage. The compensation of the feedback loop is optimized,

and output stability is insured, for a broad range of external load

capacitance extending from 500 µF (RESR = 20 mΩ) to 4,000 µF

(RESR = 2.5 mΩ). The variables that impact pulse performance

(the maximum output voltage deviation and the settling time)

are:

1. Size of step change in the output current.

2. Amount of external load capacitance.

TIME – µs

Figure 19. Predicted Response to 12 A and 24 A Step

Change in Load Current, di/dt = 12 A/µs, for CLOAD =

1000 µF and RESR = 10 mΩ

Step Change

If the step change is less than 24 A, the pulse response will im-

prove. For instance, with a 12 A step change, Figure 19 shows

a comparison of the response for a 24 A step change and a 12 A

step change in load.

Load Capacitance

Varying the external load capacitance and associated RESR be-

tween the range of CLOAD = 500 µF (RESR = 20 mΩ) and CLOAD

= 4,000 µF (RESR = 2.5 mΩ) results in the predicted waveforms

shown in Figures 20, 21, and 22. As can be seen, the larger the

capacitor, the smaller the deviation, but the longer the settling

time. Table I lists the maximum output voltage deviations and

3. Internal compensation of the feedback loop (factory set).

4. Connection from converter output to load.

Extensive modeling of the converter with ADI proprietary

software permits analysis and prediction of the impact each of

these parameters has on the pulse response. The analyses in this

settling times for the four combinations of CLOAD and RESR men-

tioned above. Note that these are based on the standard com-

pensation for the feedback loop.

Table I. Output Response to a 24 A (1 A–25 A) Step in Load

Current (Standard Compensation)

data sheet are based on the load capacitance being comprised of

100 µF, 100 mΩ tantalum load capacitors such as the CSR21

style. Figure 18 is the prediction of the standard converter’s

CLOAD

RESR

Typical

Settling Time See

Deviation (Within 1%) Figure

response to a 24 A step change in load current (from 1 A to

500 µF 20 mΩ –7%

150 µs

20

25 A) with a load capacitance of 1,000 µF (RESR = 10 mΩ).

1,000 µF 10 mΩ –6%

175 µs

18

This is very close to the measured pulse response under the

2,000 µF 5 mΩ

–5%

200 µs

21

same conditions shown in Figure 6.

4,000 µF 2.5 mΩ –4%

250 µs

22

8.1

8.1

8

8

7.9

7.9

7.8

7.8

7.7

7.7

7.6

7.6

7.5

7.4

–200 –100 0 100 200 300 400 500 600 700 800

TIME – µs

Figure 18. Predicted Response to 24 A Step Change in

Load Current, di/dt = 12 A/µs, for CLOAD = 1,000 µF and

RESR = 10 mΩ

7.5

7.4

–200 –100 0 100 200 300 400 500 600 700 800

TIME – µs

Figure 20. Predicted Response for 24 A Step Load

Change in Load Current, di/dt = 12 A/µs, for CLOAD

= 500 µF and RESR = 20 mΩ

–8–

REV. 0

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