ADM1175-1ARMZ-R7 datasheet(15/24 Pages) AD

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ADM1175

Rev. 0 | Page 15 of 24

When the initial timing cycle terminates, the device is ready to

start a hot swap operation (assuming the ON/ONB pin is asserted).

In the example shown in Figure 30, the ON pin is asserted at the

same time that VCC is applied, so the hot swap operation starts

immediately after Time Point (4). At this point, the FET gate is

charged up with a 12 μA current source. At Time Point (5), the

threshold voltage of the FET is reached, and the load current

begins to flow. The FET is controlled to keep the sense voltage

at 100 mV (this corresponds to a maximum load current level

defined by the value of RSENSE). At Time Point (6), VGATE and

VOUT have reached their full potential, and the load current has

settled to its nominal level. Figure 31 illustrates the situation

where the ON pin is asserted after VCC is applied.

VVCC

(1)

INITIAL TIMING

CYCLE

(2)

(3) (4) (5)

(6)

VON

VTIMER

VGATE

VSENSE

VOUT

Figure 30. Startup (ON Asserts as Power Is Applied)

INITIAL TIMING

CYCLE

VVCC

VON

VTIMER

VGATE

VSENSE

VOUT

(1)

(2)

(3) (4)

(5)(6)

(7)

Figure 31. Startup (ON Asserts After Power Is Applied)

HOT SWAP RETRY CYCLE ON THE ADM1175-1

AND THE ADM1175-3

With the ADM1175-1 and the ADM1175-3, the device turns off

the FET after an overcurrent fault and then uses the TIMER pin

to time a delay before automatically retrying to hot swap.

As with all ADM1175 devices, on overcurrent fault is timed by

charging the TIMER cap with a 60 μA pull-up current. When

the TIMER pin reaches 1.3 V, the fault current limit time has

been reached, and the GATE pin is pulled down. On the

ADM1175-1 and the ADM1175-3, the TIMER pin is then

pulled down with a 2 μA current sink. When the TIMER pin

reaches 0.2 V, it automatically restarts the hot swap operation.

The cool-down period is related to CTIMER by Equation 8.

tCOOL ≈ 550 × CTIMER ms/μF

(8)

Thus, the retry duty cycle is given by Equation 9.

tFAULT/(tCOOL + tFAULT ) × 100% = 3.8%

(9)

ADM1175-1ARMZ-R7 Datasheet(PDF) 15 Page - Analog Devices

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