22
ASC Breakout Board
Figure 17. 5 V Hot Swap – Fast Shutdown Circuit
Current Sense Feedback Circuit
The 5 V Hot Swap circuit on the ASC Breakout board includes a current sense feedback circuit, shown in
Figure 18. The purpose of this circuit is for demonstration and evaluation only, it does not need to be included on a
customer application board. The current sense amplifier (U2 – ZXCT1009 from Diodes, Inc) provides an output
current proportional to the voltage measured over R60. Based on the R60 resistance (5 m
Ω
) and the R94 resis-
tance (20 k
Ω
), the ratio of output voltage at TP17 (I_5V_HS) to sensed current across R60 is about 1 V / 1A (this
ratio is also maintained when Q5 and R57 are used instead of Q6 and R60). The test point I_5V_HS can be moni-
tored on an oscilloscope to confirm the Hot Swap operation and evaluate the current behavior during Hot Swap.
The internal current sense amplifier in the ASC is used in the Hot Swap algorithm, the circuit formed by U2 and
R94 is only included to provide observable current feedback during the evaluation stage.
Figure 18. 5 V Hot Swap - Current Sense Feedback Circuit
ASC INT
Connector
Fast
Shutdown
+3.3
V
ASC_5
V
_OC_SHUTDO
WN
Sheet [2]
TP16
5
V
_SD
N
1
R64
1k
Q7
2
N
3904
To Hot Swap
MOSFET Gate
I_5V_HS - 1V per 1A sensed
Demonstration Circuit to Output
Monitored Current to Test Point
(Not required for Hot Swap Operation)
R5
8
0
R60
0.005
2
W
, 1%
TP17
I_5
V
_HS
1
R59
0
R94
20k
1%
U2
ZXCT1009
V
sense+
2
V
sense-
3
Io
u
t
1
From Hot Swap
Standard MOSFET
To ASC IMON 1P
Current Monitor
To ASC IMON 1N
Current Monitor
To 5V_HS Load
Capacitor
