ADDC02808PB datasheet(10/20 Pages) AD

10 / 20 page

ADDC02808PB

REV. A

–10–

8.1

7.4

–200

800

–100

100

200

300

400

500

600

700

8.0

7.9

7.8

7.7

7.6

7.5

TIME –

Figure 25. Predicted Response for 24 A Step Load Change,

di/dt = 12 A/

µs, with Factory Set Internal Compensation

Optimized for CLOAD = 4,000 µF and RESR = 2.5 mΩ

RESPONSE AT END OF PULSE

The previous section describes how the ADDC02808PB con-

verter responds to the positive step change in load current that

occurs at the beginning of a power pulse. This section will

discuss the converter’s response at the end of the power pulse

when the load current is abruptly returned to a small value.

Figures 26-29 show the converter’s measured output voltage as

the load current is stepped from 25 A down to 4 A, 2 A, 1 A, and

0.1 A, respectively. The load capacitance is 1,000

µF with

100mV

100

100 s

Figure 26. Output Voltage Transient Response to a 25 A

to 4 A Step Change in Load, di/dt/ = 12 A/

µs, with 1,000 µF

Load Capacitance (RESR = 10 mΩ)

100mV

100

100 s

Figure 27. Output Voltage Transient Response to a 25 A

to 2 A Step Change in Load, di/dt/ = 12 A/

µs, with 1,000 µF

Load Capacitance (RESR = 10 mΩ)

RESR = 10 m

Ω. The di/dt is 12 A/µs. As can be seen, the peak

deviations for these curves are close to each other and com-

parable to the negative deviation shown in Figure 6 for a simi-

larly sized positive step change in load current.

100mV

100

100 s

Figure 28. Output Voltage Transient Response to a 25 A

to 1 A Step Change in Load, di/dt/ = 12 A/

µs, with

1,000

µF Load Capacitance (R

ESR = 10 mΩ)

100mV

100

1ms

Figure 29. Output Voltage Transient Response to a 25 A

to 0.1 A Step Change in Load, di/dt/ = 12 A/

µs, with

1,000

µF Load Capacitance (R

ESR = 10 mΩ)

What is different about these curves is the settling time. Once

the converter’s output voltage rises above nominal, the con-

verter cannot help to discharge the load capacitor. It can only

reduce its output current to zero; it cannot draw a negative

current. As such, the time it takes to bring the output voltage

back down to its nominal value depends on the load current

during the low load portion of the cycle. The rate at which the

output voltage falls to its nominal value is the load current

divided by the load capacitance (including the 150

µF capaci-

tance that is inside the converter). The smaller the load current,

the longer it takes to get the output voltage back to its nominal

value.

During the time that the output voltage is too high, the integra-

tor in the converter’s feedback circuitry is continuing to ramp

out of range. As the output voltage then falls below its nominal

value, it must have an undershoot error to bring the integrator

back into range. As can be seen from these figures, the lower

the load current, the longer the output voltage remains too

high, and the longer and the greater the output voltage under-

shoot is.

ADDC02808PB датащи(PDF) 10 Page - Analog Devices

ADDC02808PB датащи(HTML) 10 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

датащи скачать

ссылки URL