sc4150his-4tr Semtech Corporation, sc4150his-4tr Datasheet - Page 6

• Manufacturer Part Number: sc4150his-4tr
• Description: Sc4150 Negative-voltage Hot-swap Controller
• Manufacturer: Semtech Corporation

Insertion of a power circuit board into a live backplane
would draw enormous inrush currents. This is mostly due
to the charging of the bulk electrolytic capacitors at the
input of the power module being plugged in.
The transient currents would send glitches all over the
power system and could cause corruption of the signals
and even a power down if the source isn’t able to handle
these high surges.
This section describes the components selection needed
for a typical application utilizing the SC4150. Let’s assume
the following requirements for a representative system:
Input voltage range: 36V to 72V
Nominal current: 2A typ.
Over-current condition: 5A
Bulk capacitance: Cload = 150µF
The schematic in Figure 2 combines internal function
blocks along with the external components of the
application circuit.
POWER MANAGEMENT
Applications Information
2004 Semtech Corp.
C1
+48V
-48V
R1
R2
R3
UV
OV
Vee
Vcc
60mV
R4
12.5V Reg
SENSE
+
+
+
_
_
_
Delay
1.223V
C2
+
_
Figure 2
+7V
GATE
6
R6
Resistors R1, R2 and R3 make up a voltage divider to
set the Under-Voltage (UV) and Over-Voltage (OV) trip
points.
When the input power supply ramps up the UV trips at
1.273V and OV trips at 1.223V; during the ramp down
transition the UV trips at 1.223V and OV trips at 1.198V.
The 50mV hysteresis for UV and 25mV hysteresis for OV
provide the necessary guard-bands to prevent false
tripping during power up and power down conditions.
As an additional noise killing and stabilizing measure, the
capacitor C1 should be placed at the OV terminal with
the value in range from 1,000 to 10,000pF.
For the UV=38V and OV=70V the values of the resistor
can be calculated as follows:
Vuv = 1.273V · (R1+R2+R3) ÷ (R2+R3)
Vov = 1.223V · (R1+R2+R3) ÷ R3
R5
Q1
C3
DRAIN
Timer
50uA
_
+
1.75V
PWRGD
Cload
150uF
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SC4150