ADP1043A datasheet(17/72 Pages) AD

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ADP1043A

Rev. 0 | Page 17 of 72

OrFET Operation Examples

Hot Plug into a Live Bus

A new PSU is plugged into a live 12 V bus (yellow). The internal

voltage VS1 (red) is ramped up before the OrFET is turned on.

After the OrFET is turned on (green), current in the new PSU

begins to flow to the load (blue). The turn-on voltage threshold

between the new PSU and the bus is programmable.

CH2 2.00V

CH4 10.0V

CH1 2.00V

CH3 2.00A

M10.0ms

A CH4

100mV

CS2

VS3

VS1

OrFET

Figure 17. Hot Plug into a Live Bus (Yellow Is Bus Voltage; Red Is VS1 Voltage;

Green Is OrFET Control Signal; Blue Is Load Current)

Runaway Master

A rogue PSU on the bus (yellow) has a fault condition, and the

result is that the bus voltage increases above the OVP threshold.

The good PSU turns off the OrFET (green) and regulates its

internal voltage VS1 (red). When the rogue power supply fault

condition is removed, the bus voltage decreases. The OrFET of

the good PSU is immediately turned on and the good PSU

resumes regulating from VS3.

CH2 2.00V

CH4 10.0V

CH1 2.00V

CH3 2.00A

M50.0ms

A CH4

0mV

CS2

VS3

VS1

OrFET

Figure 18. Runaway Master (Yellow Is Bus Voltage; Red Is VS1 Voltage;

Green Is OrFET Control Signal; Blue Is Load Current)

Short Circuit

When one of the output rectifiers fails, the bus voltage can

collapse if the OrFET is not promptly turned off. The fast

OrFET comparator is used to protect the system from this fault

event. Figure 19 shows a short circuit applied to the output

capacitors, before the OrFET. After the fast OrFET threshold for

CS2 (blue) is triggered, the OrFET (green) is turned off. In this

case, the gate driver is not very fast and takes about 500 ns. (A

larger buffer to drive the OrFET would turn it off quicker.)

Figure 19 also shows the operation when the short circuit is

removed. The internal regulation point, VS1 (red), returns to

12 V, and the OrFET (green) is reenabled. The PSU again begins

to contribute current to the load (blue).

CH2 2.00V

CH4 10.0V

CH1 2.00V

CH3 2.00A

M200.0ms

A CH4

7.5mV

CS2

VS3

OrFET

VS1

Figure 19. Internal Short Circuit (Yellow Is Bus Voltage; Red Is VS1 Voltage;

Green Is OrFET Control Signal; Blue Is Load Current)

Light Load Mode Operation

PSU 1 increases its voltage at light load from 12 V to 12.1 V

(yellow). Both PSU 1 and PSU 2 are CCM, so PSU 1 sources

current and PSU 2 sinks current (blue). In PSU 2, after 10 ms

the accurate OrFET control turns off the OrFET to prevent

reverse current from flowing. Note that the OrFET voltage

(green) is solid during this transition because PSU 1 and PSU 2

are in CCM mode.

CH2 2.00V

CH4 10.0V

CH1 2.00V

CH3 2.00A

M5.0ms

A CH4

8.3mV

CS2

VS3

OrFET

VS1

Figure 20. Light Load Mode (Yellow Is Bus Voltage; Red Is VS1 Voltage;

Green Is OrFET Control Signal; Blue Is Load Current)

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