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Negative Voltage Hot Swap Controller
POWER MANAGEMENT Description
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 operation limits the maximum current even under short circuit conditions. A built in timing circuit prevents false shutdown. 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 condition 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.
SC4150
Features
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
Applications
Central office switching -48V Distributed power systems Power supply hotswap & inrush control
Typical Application Circuit
GND C1 0.1
8
PWRGD/PWRGD
1
U1 SC4150
PWRGD /PWRGD VCC
GND(remote) R1 562k
2 OV DRAIN 7
VEE Vee
R6 18k
3 UV GATE 6
C4 3.3nF
C5 150
R2 9.31k
4
VEE
SENSE
5
R5 10 R3 10.2k -- 48V C2 0.001 R4 0.01 C3 0.33
Q1
Figure 1
Revision: April 14, 2004
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SC4150
POWER MANAGEMENT Absolute Maximum Ratings
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.
Parameter Supply Voltage DRAIN, PWRGD/ PWRGD SENSE, GATE UV, OV Thermal Resistance Junction to Ambient Thermal Resistance Junction to Case Operating Junction Temperature Range Storage Temperature Range Lead Temperature (Soldering) 10 sec
Symbol V CC
Maximum -0.3 to 100 -0.3 to 100 -0.3 to 20 -0.3 to 60
Units V V V V C C C C C
J A J C TJ TSTG TLEAD
163 38.8 -40 to 125 -65 to 150 300
Electrical Characteristics
Unless specified: TA = 25C, VCC = 48V, VEE = 0V. Values in bold apply over full operating temperature range.
Parameter DC Characteristics Supply Operating Range Supply Current Circuit Breaker Trip Voltage Gate Pin Pull-up Current Gate Pin Pull-down Current Sense Pin Current External Gate Drive
Symbol
Test Conditions
Min
Typ
Max
Units
V CC ICC V CB IPU IPD ISENSE VGATE UV = 3V, 0V = VEE, SENSE = VEE VCB = (VSENSE - VEE) Gate drive ON, VGATE = VEE Any fault condition VSENSE = 50mV (VGATE -VEE), 20V < VDD 80V (VGATE -VEE), 10V VDD 20V
10 4 50 60 -50 40 -0.05 9 13 8 1.241 1.192 1.273 1.223 50 VUV = VEE OV Low to High transition OV High to Low transition 1.192 1.153 -0.1 1.223 1.188 35 VOV 1.5V
2
80 7 70
V mA mV A mA A
16
V
UV Pin High Threshold Voltage UV Pin Low Threshold Voltage UV Pin Hystersis UV Pin Input Current OV Pin High Threshold Voltage OV Pin Low Threshold Voltage OV Pin Hystersis OV Pin Input Current
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VUVH VUVL VUVHY IINUV VOVH VOVL VOVHY IINOV
UV Low to High transition UV High to Low transition
1.305 1.253
V V mV A
1.253 1.223
V V mV A
-0.05
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SC4150
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: TA = 25C, VCC = 48V, VEE = 0V. Values in bold apply over full operating temperature range.
Parameter Power Good Threshold Power Good Threshold Hysteresis Drain Input Bias Current Output Low Voltage
Symbol V PG VPGHY IDRAIN VOL
Test Conditions VDRAIN - VEE, High to Low transition
Min 1.5
Typ 1.75 0.4
Max 2.0
Units V V
VDRAIN = 48V SC4150H, VOL = PWRGD - VDRAIN @ VDRAIN = 5V, IO = 1mA SC4150L, VOL = PWRGD - VEE @ VDRAIN = 1V, IO = 1mA
15 1 1 1.0 1.0
50
A V V
Output Leakage
IOH
SC4150H, VDRAIN -VEE = 1V, VPWRGD = 80V SC4150L, VDRAIN -VEE = 5V
10 10
A A
AC Characteristics OV High to Gate Low UV Low to Gate Low OV Low to Gate High UV Low to Gate High SENSE High to Gate Low DRAIN Low to PWRGD Low DRAIN Low to (PWRGD - DRAIN) High DRAIN High to PWRGD High DRAIN High to (PWRGD - DRAIN) Low Gate ON Time - Time Delay Gate ON Time - Time Delay Gate OFF Time tPHLOV tPHLUV tPLHOV tPLHUV tPHLSENSE tPHLPG 1.7 1.5 5.5 6.5 3 0.5 0.5 s s s s s s
tPLHPG
s
tON_1 tON_2 tOFF
VDRAIN > 8V, after short circuit VDRAIN < 7V, after short circuit SC4150, After short, prior to retry SC4150-4, After short, prior to retry
5 250 100 400
s s ms
Note: (1) This device is ESD sensitive. Use of standard ESD handling precaution is required.
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SC4150
POWER MANAGEMENT Pin Configuration
TOP VIEW
PWRGD/PWRGD OV UV VEE 1 2 3 4 8 7 6 5 VCC DRAIN GATE SENSE
Ordering Information
Part Number(1)(2)(3) SC4150HISTRT SC4150LISTRT SC4150HIS-4TRT SC4150LIS-4TRT P ackag e SO-8
(SO-8)
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.
Pin Descriptions
Pin 1 2 Pin Name PWRGD/PWRGD OV Pin Function Power Good output pin. This pin will toggle when VDRAIN is within VPG of VEE. This pin can be connected directly to the enable pin of a power module, 0.1F to VEE is optional. Analog Overvoltage input. When OV is pulled above 1.223V threshold, an overvoltage condition is detected and the GATE pin will be immediately pulled low. The GATE pin will remain low until OV drops below the 1.188V high to low threshold. Analog Undervoltage input. When UV is pulled below the 1.223V threshold, an undervoltage condition is detected and the GATE pin will be immediately pulled low. The GATE pin will remain low until UV rises above the 1.273 threshold. Negative supply voltage input. Connect to the lower potential of the power supply. Circuit breaker sense pin. With a sense resistor placed in the supply path between VEE and SENSE, the circuit breaker will trip when the voltage across the resistor exceeds 60mV. Noise spikes of less than 2s are filtered out and will not trip the circuit breaker. If the circuit breaker trip current is set to twice the normal operating current, only 25mV is dropped across the sense resistor during normal operation. To disable the circuit breaker, VEE and SENSE can be shorted together. Gate drive output for external n-channel. The GATE pin will go high when the following start-up conditions are met: the UV pin is high, t he OV pin is low and (VSENSE - VEE) < 60mV. The GATE pin is pulled high by a 50A current source and pulled low with a 40mA current source. Analog Drain sense input. Connect this pin to the drain of the external N-channel FET and the V(-) pin of the power module. When the DRAIN pin is below VPG, the PWRGD or PWRGD pin will toggle. Positive supply voltage input. Connect this pin to the higher potential of the power supply input and the V(+) pin of the power module.
3
UV
4 5
VEE SENSE
6
GATE
7
DRAIN
8
VC C
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SC4150
POWER MANAGEMENT Block Diagram
Active High PWRGD
Vcc PWRGD
12.5V Reg
1.223V
50uA UV _ +
_ OV Timer + _ + _ Delay _
60mV 1.75V
+7V
+
+
Vee
SENSE
GATE
DRAIN
Active Low PWRGD
Vcc
PWRGD
12.5V Reg
1.223V
50uA UV _ +
_ OV Timer + _ + +7V
Delay _
60mV
_
+
1.75V
+
Vee
SENSE
GATE
DRAIN
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SC4150
POWER MANAGEMENT Applications Information
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 = 150F The schematic in Figure 2 combines internal function blocks along with the external components of the application circuit.
+48V
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
Vcc
PWRGD
12.5V Reg
R1
1.223V
50uA UV _ +
R2
_ OV Timer + _ +
C1 R3
+7V
Delay _
60mV
_
+
1.75V
+
Vee
SENSE
GATE
R5
DRAIN
C3 Cload 150uF R6
C2
-48V
R4
Q1
Figure 2
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SC4150
POWER MANAGEMENT Applications Information (Cont.)
With the input bias current of the UV and OV comparators in the range of 20-30nA, let's choose the R1 to be 562k. This yields the values of R2=9.31k and R3 = 10.2k. 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 m. 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 shor t 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 = 150F * 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.
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The inrush can be calculated using the following equation: IMAX = (50A * 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 = Inom * 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 = 0.2, and will dissipate Pdis = 2 * 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 5 to 20.
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SC4150
POWER MANAGEMENT Typical Characteristics
Below are the snap-shots taken at start-up with different loading conditions and during the application of the overcurrent 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 4. Start-up in over load.
Figure 5. Start-up with 1Amp load.
Figure 6. From 3A load into "short circuit".
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SC4150
POWER MANAGEMENT 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.
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SC4150
POWER MANAGEMENT Evaluation Board Schematic
GND U1 SC4150H/L GND(remote)
1 PWRGD/PWR GD VC C 8
R7 (opt)
Copt 0.1
C1 0.1 R1 562k
2 OV DR AIN 7
ON/OFF +Vin R6 18k
3 UV GATE 6
+Vout
C4 3.3nF
C5 150
C6(opt) 0.1
POWER MODULE
-Vin -Vout
R2 9.31k
4
VEE
SENSE
5
R3 10.2k -- 48V
C2(opt) 0.01 R4 0.01
R5 10 C3 0.33 Q1 IRF1310
Evaluation Board
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SC4150
POWER MANAGEMENT Evaluation Board - Bill of Materials
R ef 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Qty 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 C1 C2 (opt.) C3 C4 C5 C6 (opt.) Q1 R1 R2 R3 R4 R5 R6 R7 U1 Designator 0.1/100V 0.01 0.33 0.0033/100V 150/80V 0.1/100V IRF1310 562k 9.31k 10.2k 0.01 10 18k 5.1k S C 4150 Value Description Ceramic cap Ceramic cap Ceramic cap Ceramic cap Aluminum cap Ceramic cap MOSFET Resistor Resistor Resistor Resistor Resistor Resistor Resistor Semtech IC Footprint 1210 0805 1206S 0805 CAP-AL-H 1210 D2PAK 0805 0805 0805 2010C S 0805 0805 1206S SO-8
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SC4150
POWER MANAGEMENT Outline Drawing - SO-8
JEDEC REF: MS-012AA
Minimum Land Pattern - SO-8
Contact Information
Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804
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