ADDC02808PBKV Analog Devices, ADDC02808PBKV Datasheet - Page 8

• Manufacturer Part Number: ADDC02808PBKV
• Description: 28 V/ 200 W Pulsed DC/DC Converter with Integral EMI Filter
• Manufacturer: Analog Devices

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 F (R
(R
(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.
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 F, 100 m 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 F (R
This is very close to the measured pulse response under the
same conditions shown in Figure 6.
ADDC02808PB
Figure 17. Largest On-State Power vs. Pulsewidth that
Maintains T
Figure 18. Predicted Response to 24 A Step Change in
Load Current, di/dt = 12 A/ s, for C
R
ESR
ESR
= 2.5 m ). The variables that impact pulse performance
= 10 m
250
200
150
100
8.1
7.9
7.8
7.7
7.6
7.5
7.4
50
–200
0
8
0
–100
JMAX
100W ave
25
0
MAXIMUM CONTINUOUS
110 C at 90 C Baseplate
100
POWER LIMIT
50
PULSEWIDTH – ms
200
50W ave
TIME – s
MAXIMUM PEAK
300
75
POWER LIMIT
400
ESR
10W ave
100
LOAD
500
= 20 m ) to 4,000 F
ESR
= 1,000 F and
600
125
= 10 m ).
700
150
800
–8–
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 R
tween the range of C
= 4,000 F (R
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 C
mentioned above. Note that these are based on the standard
compensation for the feedback loop.
Table I. Output Response to a 24 A (1 A–25 A) Step in Load
Current (Standard Compensation)
C
500 F
1,000 F
2,000 F
4,000 F
Figure 19. Predicted Response to 12 A and 24 A Step
Change in Load Current, di/dt = 12 A/ s, for C
1000 F and R
LOAD
= 500 F and R
Figure 20. Predicted Response for 24 A Step Load
Change in Load Current, di/dt = 12 A/ s, for C
8.1
7.9
7.8
7.7
7.6
7.5
7.4
–200
8
8.1
7.9
7.8
7.7
7.6
7.5
7.4
–200
8
–100
R
20 m
10 m
5 m
2.5 m
–100
ESR
ESR
ESR
= 2.5 m ) results in the predicted waveforms
0
ESR
0
= 10 m
LOAD
100
= 20 m
100
Typical
Deviation
–7%
–6%
–5%
–4%
= 500 F (R
200
24A STEP CHANGE
12A STEP CHANGE
200
TIME – s
TIME – s
300
300
400
400
Settling Time
(Within 1%)
150 s
175 s
200 s
250 s
ESR
500
500
= 20 m ) and C
600
LOAD
600
700
and R
700
LOAD
800
LOAD
800
ESR
ESR
See
Figure
20
18
21
22
=
REV. A
be-
LOAD