Datasheet

ADM1175 Data Sheet
Rev. C | Page 14 of 24
When the initial timing cycle terminates, the device is ready to
start a hot swap operation (assuming that the ON/ONB pin is
asserted). In the example shown in Figure 30, the ON pin is
asserted at the same time that V
CC
is applied; therefore, the hot
swap operation starts immediately after Time Point 4. At this
point, the FET gate is charged up with a 12.5 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 maxi-
mum load current level defined by the value of R
SENSE
).
At Time Point 6, V
GATE
and V
OUT
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 V
CC
is applied.
V
VCC
(1)
INITIAL TIMING
CYCLE
(2) (3)(4)(5) (6)
V
ON
V
TIMER
V
GATE
V
SENSE
V
OUT
05647-004
Figure 30. Startup (ON Asserts as Power Is Applied)
INITIAL TIMING
CYCLE
V
VCC
V
ON
V
TIMER
V
GATE
V
SENSE
V
OUT
(1) (2) (3)(4) (5)(6) (7)
05647-005
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, an overcurrent fault is timed by
charging the TIMER capacitor with a 60 μA pull-up current.
When the TIMER pin reaches 1.3 V, the fault current limit time
is 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 auto-
matically restarts the hot swap operation.
The cooldown period is related to C
TIMER
by Equation 8.
t
COOL
≈ 550 × C
TIMER
ms/μF (8)
Therefore, the retry duty cycle is as given by Equation 9.
t
FAULT
/(t
COOL
+ t
FAULT
) × 100% = 3.8% (9)