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SC4150
Negative Voltage
Hot Swap Controller
POWER MANAGEMENT
Revision: April 14, 2004
Programmable slew of the inrush current when
used for hot insertion in the negative 24V and 48V
backplane
Closed loop operation limits the maximum current
even in short circuit condition
Built in timer prevents false shutdown, when the
closed loop operation limits the current.
Sensing the drain voltage allows for immediate
shutdown in short circuit condition, where current
spikes and noise is ignored.
Power good signal
Input UVLO and OVLO sensing
SO-8 package
Central office switching
-48V Distributed power systems
Power supply hotswap & inrush control
Description Features
Applications
Typical Application Circuit
The SC4150 is a negative voltage hotswap controller that
allows the insertion of line cards into a live backplane.
The inrush current is programmable and closed loop op-
eration limits the maximum current even under short cir-
cuit conditions. A built in timing circuit prevents false shut-
down. The signal from the drain voltage is fed to the
timer, providing safety for the MOSFET when in linear
mode. The SC4150 latches off under abnormal condi-
tion and attempts to restart after a time out period.
The device comes in two options, PWRGD (SC4150H)
and PWRGD (SC4150L). These signals can be directly
used to enable power modules.
Figure 1
Q1
C3
0.33
C5
150
GND
-- 48V
R5
10
R1
562k
R3
10.2k
R4
0.01
R6
18k
R2
9.31k
C4
3.3nF
DRAIN 7
UV
3
VEE
4
GATE 6
PWRGD
1
SENSE 5
VCC 8
OV
2
U1
SC4150
GND(remote)
C2
0.001
C1
0.1
Vee
PWRGD/PWRGD
/PWRGD VEE
22004 Semtech Corp. www.semtech.com
SC4150
POWER MANAGEMENT
Absolute Maximum Ratings
Electrical Characteristics
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters
specified in the Electrical Characteristics section is not implied.
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Unless specified: TA = 25°C, VCC = 48V, VEE = 0V.
Values in bold apply over full operating temperature range.
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32004 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC4150
Electrical Characteristics (Cont.)
Unless specified: TA = 25°C, VCC = 48V, VEE = 0V.
Values in bold apply over full operating temperature range.
Note:
(1) This device is ESD sensitive. Use of standard ESD handling precaution is required.
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42004 Semtech Corp. www.semtech.com
SC4150
POWER MANAGEMENT
Notes:
(1) Only available in tape and reel packaging. A reel
contains 2500 devices.
(2) Device marking:
SC4150H, SC4150L - 100ms
4150H-4, 4150L-4 - 400ms
(3) Lead free product.
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TRT4-SIL0514CS
Pin Configuration Ordering Information
Pin Descriptions
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1
2
3
4
VCCPWRGD/PWRGD
TOP VIEW
(SO-8)
5
6
7
8
DRAINOV
GATEUV
SENSEVEE
52004 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC4150
Block Diagram
Active Low PWRGD
Active High PWRGD
60mV
+
_
_
+
_
+
_
+
+
_
+7V
Delay
DRAINGATESENSEVee
Vcc
12.5V Reg 1.223V
1.75V
PWRGD
50uA
UV
OV Timer
60mV
+
_
_
+
_
+
_
+
+
_
+7V
Delay
DRAINGATESENSEVee
Vcc
12.5V Reg 1.223V
1.75V
PWRGD
50uA
UV
OV Timer
62004 Semtech Corp. www.semtech.com
SC4150
POWER MANAGEMENT
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.
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
Applications Information
Figure 2
60mV
+
_
_
+
_
+
_
+
+
_
+7V
Delay
DRAINGATESENSEVee
Vcc
12.5V Reg 1.223V
1.75V
PWRGD
50uA
UV
OV Timer
Q1
R4
Cloa d
150uF
C3
R5
R1
R2
R3
C2
-48V
+48V
C
1
R6
72004 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC4150
With the input bias current of the UV and OV comparators
in the range of 20-30nA, let’s choose the R1 to be
562kΩ. This yields the values of R2=9.31kΩ and R3 =
10.2kΩ. With these values the accuracy is about 1%
which is quite acceptable for those functions.
Resistor R4 sets the over-current trip. To choose R4,
the user must determine the level of the current where
it should trip. As a rule of thumb, the over-current is set
to be 200-300% of the nominal value. In our case, we
assumed this value to be 5A.
Considering the minimum trip voltage is 50mV the value
of R4 is 50mV ÷ 5A = 10 mΩ.
The tolerance of this resistor is usually price driven and
5% is an adequate range of accuracy.
The actual position and layout of the circuitry around the
sense resistor R4 is critical to avoid a false over-current
tripping. The trace routing between R4 and SC4150
should be as short as possible and wide enough to handle
the maximum current with zero current in the sense lines
– ideally “Kelvin” like.
Additionally, there is a short delay circuit at the
comparator to filter out unwanted noise and otherwise
induced transients.
Inrush Current
is being controlled by the R5C3 network
and swamping capacitor C2.
When a board is plugged into a live backplane, the input
bulk capacitance of the board’s power supply produces
large current transients due to the rush of the currents
charging those capacitors. The main feature of the
SC4150 is to provide an orderly and well-controlled inrush
current.
Since the minimum trip voltage is 50mV, let’s choose
the inrush current to be 3A.
Imax = Cload · ∆Vmax /dt
dt = Cload · ∆Vmax /Imax = 150µF · 70V / 3A = 3.5ms
This would be the minimum time for the gate voltage
plateau during which the Vdd linearly decreases
maintaining 3A charge current of the Cload.
The inrush can be calculated using the following equation:
IMAX = (50µA • CLOAD) / C3
With the values shown in the schematic the actual inruch
current will be about 2A, which is within the limits we
have chosen.
Resistor R5 will produce a time constant which prevents
Q1 from turning on when power is initially applied and
the circuit is not ready to actively pull the gate low. It’s
value is not critical and 18k ensures the adequate delay.
The value of C2 is chosen to prevent false turn-on of the
FET due to the current flowing via C3 into the gate of the
FET when the circuit initially connects to the power source.
Capacitors C2 and C3 form a divider from Vin to GND.
C2 must keep the initial voltage at the gate below Vth
minimum.
For the typical FET, this threshold is around 1V to 2V,
therefore C2 = 100 • C3 will keep gate voltage at 0.7V,
even at the ”worst” case of Vin = 70V.
The choice of the Q1 is quite straightforward and is guided
mostly by thermal considerations due to the power
dissipation in the steady state.
For instance, in our case, the nominal current is 2A, the
power dissipation due to the conducting losses will be
Pdis = Inom² • Rds_on.
The MOSFET should be able to withstand Vdss ≥ 100V
with continuous drain current Id ≥ 6A. Device SUD06N10
or similar fits this application. It has an Rds_on = 0.2Ω,
and will dissipate
Pdis = 2² • 0.2 = 0.8W, which can be handled by this
DPAK device.
If there is a consideration of reducing the temperature
of the MOSFET then the lower Rds_on device should be
chosen or a different style (D2PAK) which has lower
Junction-to-Ambient thermal characteristics.
The R6
has a function of dumping high frequency
oscillations. The value of it is not critical and can be in
the range of 5Ω to 20Ω.
Applications Information (Cont.)
82004 Semtech Corp. www.semtech.com
SC4150
POWER MANAGEMENT
Typical Characteristics
Below are the snap-shots taken at start-up with different loading conditions and during the application of the over-
current at the output of the circuit.
For all figures, Ch1: VDRAIN; Ch2: VGATE; Ch3: PWRGD; Ch4: VR4 (Input current)
Figure 3. Start-up with no load.
Figure 5. Start-up with 1Amp load.
Figure 4. Start-up in over load.
Figure 6. From 3A load into “short circuit”.
92004 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC4150
Typical Characteristics (Cont.)
The following set of snapshots demonstrates effectiveness of SC4250 circuit in the case where connection to the
live back plane is very “bouncy”, which is usually the situation with manual replacements of the power cards.
For all figures, Ch1: VDRAIN; Ch2: VGATE; Ch3: PWRGD (referenced to VDRAIN); Ch4: VR4 (Input current)
Figure 7. Short circuit hiccup. Figure 8. Inrush limit.
Figure 9. Inrush limit. Figure 10. Inrush limit.
102004 Semtech Corp. www.semtech.com
SC4150
POWER MANAGEMENT
Evaluation Board Schematic
Evaluation Board
C3
0.33
C5
150
+Vout
-Vout
GND
-- 48V
R5
10
R1
562k
R3
10.2k
R4
0.01
R6
18k
R2
9.31k
C4
3.3nF
DRAIN 7
UV
3
VEE
4
GATE 6
PWRGD/PWRGD
1
SENSE 5
VCC 8
OV
2
U1
SC4150H/L
GND(remote)
C2(opt)
0.01
+Vin
-Vin
ON/OFF
POWER
MODULE
C1
0.1
C6(opt)
0.1
R7
(opt) Copt
0.1
Q1
IRF1310
112004 Semtech Corp. www.semtech.com
POWER MANAGEMENT
SC4150
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Evaluation Board - Bill of Materials
122004 Semtech Corp. www.semtech.com
SC4150
POWER MANAGEMENT
JEDEC REF: MS-012AA
Outline Drawing - SO-8
Minimum Land Pattern - SO-8
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
Contact Information
Mouser Electronics
Authorized Distributor
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