ADDC02808PB
250
8.1
8
MAXIMUM PEAK
POWER LIMIT
200
7.9
7.8
7.7
7.6
10W ave
100W ave
150
12A STEP CHANGE
24A STEP CHANGE
50W ave
100
MAXIMUM CONTINUOUS
POWER LIMIT
50
0
7.5
7.4
0
25
50
75
100
125
150
–200 –100
0
100 200 300 400 500 600 700 800
PULSEWIDTH – ms
TIME – s
Figure 17. Largest On-State Power vs. Pulsewidth that
Maintains TJMAX ≤ 110°C at 90°C Baseplate
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
=
TRANSIENT RESPONSE
The standard ADDC02808PB is designed to deliver large
changes, or pulses, in load current with minimum output volt-
age 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.
3. Internal compensation of the feedback loop (factory set).
4. Connection from converter output to load.
Step Change
If the step change is less than 24 A, the pulse response will
improve. 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
settling times for the four combinations of CLOAD and RESR
mentioned above. Note that these are based on the standard
compensation for the feedback loop.
Extensive modeling of the converter with ADI proprietary soft-
ware permits analysis and prediction of the impact each of these
parameters has on the pulse response. The analyses in this 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
response to a 24 A step change in load current (from 1 A to
25 A) with a load capacitance of 1,000 µF (RESR = 10 mΩ).
This is very close to the measured pulse response under the
same conditions shown in Figure 6.
Table I. Output Response to a 24 A (1 A–25 A) Step in Load
Current (Standard Compensation)
Typical
Deviation (Within 1%)
Settling Time See
CLOAD
RESR
Figure
500 µF
20 mΩ
10 mΩ
5 mΩ
–7%
–6%
–5%
–4%
150 µs
175 µs
200 µs
250 µs
20
18
21
22
1,000 µF
2,000 µF
4,000 µF
2.5 mΩ
8.1
8
8.1
8
7.9
7.8
7.7
7.6
7.9
7.8
7.7
7.6
7.5
7.4
7.5
7.4
–200 –100
0
100 200 300 400 500 600 700 800
–200 –100
0
100 200 300 400 500 600 700 800
TIME – s
TIME – s
Figure 18. Predicted Response to 24 A Step Change in
Load Current, di/dt = 12 A/µs, for CLOAD = 1,000 µF and
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
RESR = 10 mΩ
–8–
REV. A
ADI [ ADI ]
