ISL6142 Datasheet, PDF (21/23 Pages) Intersil Corporation – Negative Voltage Hot Plug Controller

ISL6142, ISL6152
The switch SW1 is shown as a simple push button. It can be
replaced by an active switch, such as an NPN or NFET; the
principle is the same; pull the UV node below its trip point,
and then release it (toggle low). To connect an NFET, for
example, the DRAIN goes to UV; the source to -V_IN, and the
GATE is the input; if it goes high (relative to -V_IN), it turns the
NFET on, and UV is pulled low. Just make sure the NFET
resistance is low compared to the resistor divider, so that it
has no problem pulling down against it.
R12 is a pull-up resistor for PWRGD, if there is no other
component acting as a pull-up device. The value of R12 is
determined by how much current is needed when the pin is
pulled low (also affected by the V_DD voltage); and it should
be pulled low enough for a good logic low level. An LED can
also be placed in series with R12, if desired. In that case, the
criteria is the LED brightness versus current.
GND
(SHORT PIN)
GND
GND
-48V IN
Logic
Supply
R10 (V_EE+5V)
R4
R5
D1* Logic
Input
SW1*
TO
ADC ^R6
Q2
R9
C4*
R11*
FAULT
DIS
IS_OUT
UV
V_DD
ISL6142
PWRGD
OV
CT V_EE IS-
IS+ SENSE GATE
DRAIN
C3
R7
R8
C1
R3
R2
C2
R1
Q1
FIGURE 38. ISL6142/52 OPTIONAL COMPONENTS (SHOWN WITH *)
R12*
CL
RL
-48V OUT
Applications: Layout Considerations
For the minimum application, there are 10 resistors, 3
capacitors, one IC and 2 FETs. A sample layout is shown in
Figure 39. It assumes the IC is 8-SOIC; Q1 is in a D2PAK (or
similar SMD-220 package).
Although GND planes are common with multi-level PCBs, for
a -48V system, the -48V rails (both input and output) act
more like a GND than the top 0V rail (mainly because the IC
signals are mostly referenced to the lower rail). So if
separate planes for each voltage are not an option, consider
prioritizing the bottom rails first.
Note that with the placement shown, most of the signal lines
are short, and there should be minimal interaction between
them.
Although decoupling capacitors across the IC supply pins
are often recommended in general, this application may not
need one, nor even tolerate one. For one thing, a decoupling
cap would add to (or be swamped out by) any other input
capacitance; it also needs to be charged up when power is
applied. But more importantly, there are no high speed (or
any) input signals to the IC that need to be conditioned. If still
desired, consider the isolation resistor R10, as shown in
figure 38.
NOTE:
1. Layout scale is approximate; routing lines are just for illustration
purposes; they do not necessarily conform to normal PCB
design rules. High current buses are wider, shown with parallel
lines.
2. Approximate size of the above layout is 0.8 x 0.8 inches,
excluding Q1 (D2PAK or similar SMD-220 package).
3. R1 sense resistor is size 2512; all other R’s and C’s shown are
0805; they can all potentially use smaller footprints, if desired.
4. The RL and CL are not shown on the layout.
5. Vias are needed to connect R4 and V_DD to GND on the bottom
of the board, and R8 to pin 9; all other routing can be on the top
level.
6. PWRGD signal is not used here.
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