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LTC4361-1/LTC4361-2 Overvoltage/Overcurrent Protection Controller FEATURES
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DESCRIPTION
The LTC(R)4361 overvoltage/overcurrent protection controller safeguards 2.5V to 5.5V systems from input supply overvoltage. It is designed for portable devices with multiple power supply options including wall adaptors, car battery adaptors and USB ports. The LTC4361 controls an external N-channel MOSFET in series with the input power supply. During overvoltage transients, the LTC4361 turns off the MOSFET within 1s, isolating downstream components from the input supply. Inductive cable transients are absorbed by the MOSFET and load capacitance. In most applications, the LTC4361 provides protection from transients up to 80V without requiring transient voltage suppressors or other external components. The LTC4361 has a delayed start-up and adjustable dV/dt ramp-up for inrush current limiting. A PWRGD pin provides power good monitoring for VIN. The LTC4361 features a soft shutdown controlled by the ON pin and drives an optional external P-channel MOSFET for negative voltage protection. Following an overvoltage condition, the LTC4361 automatically restarts with a start-up delay. After an overcurrent fault, the LTC4361-1 remains off while the LTC4361-2 automatically restarts after a 130ms start-up delay.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and ThinSOT, Hot Swap, No RSENSE and PowerPath are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
2.5V to 5.5V Operation Overvoltage Protection Up to 80V No Input Capacitor or TVS Required for Most Applications 2% Accurate 5.8V Overvoltage Threshold 10% Accurate 50mV Overcurrent Circuit Breaker <1s Overvoltage Turn-Off, Gentle Shutdown Controls N-Channel MOSFET Adjustable Power-Up dV/dt Limits Inrush Current Reverse Voltage Protection Power Good Output Low Current Shutdown Latchoff (LTC4361-1) or Auto-Retry (LTC4361-2) After Overcurrent Available in 8-Lead ThinSOTTM and 8-Lead (2mm x 2mm) DFN Packages
APPLICATIONS
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USB Protection Handheld Computers Cell/Smart Phones MP3/MP4 Players Digital Cameras
TYPICAL APPLICATION
Protection from Overvoltage and Overcurrent
VIN 5V 0.025 Si1470DH COUT GATE SENSE OUT IN LTC4361 ON PWRGD GND
436112 TA01a
Output Protected from Overvoltage at Input
VIN
VOUT 5V 1.5A
VOUT VIN, VOUT 5V/DIV VGATE 10V/DIV
0.5s/DIV Si1470DH COUT = 10F
436112 TA01b
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LTC4361-1/LTC4361-2 ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
Bias Supply Voltage (IN) ............................ -0.3V to 85V Input Voltages SENSE ................................................... -0.3V to 85V OUT, ON ................................................... -0.3V to 9V Output Voltages PWRGD.................................................... -0.3V to 9V GATE (Note 3) ........................................ -0.3V to 15V GATEP.................................................... -0.3V to 85V IN to GATEP ........................................... -0.3V to 10V
Operating Temperature Range LTC4361C ................................................ 0C to 70C LTC4361I .............................................-40C to 85C Storage Temperature Range .................. -65C to 150C Lead Temperature (Soldering, 10 sec) TSOT................................................................. 300C
PIN CONFIGURATION
TOP VIEW TOP VIEW ON 1 OUT 2 GATEP 3 GND 4 8 PWRGD 7 GATE 6 SENSE 5 IN GND 1 GATEP 2 OUT 3 ON 4 9 8 IN 7 SENSE 6 GATE 5 PWRGD
TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 TJMAX = 125C, JA = 195C/W
DC PACKAGE 8-LEAD (2mm 2mm) PLASTIC DFN TJMAX = 125C, JA = 102C/W EXPOSED PAD (PIN 9) IS GND, CONNECTION OPTIONAL
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI) LTC4361CTS8-1#TRMPBF LTC4361CTS8-2#TRMPBF LTC4361ITS8-1#TRMPBF LTC4361ITS8-2#TRMPBF LTC4361CDC-1#TRMPBF LTC4361CDC-2#TRMPBF LTC4361IDC-1#TRMPBF LTC4361IDC-2#TRMPBF TAPE AND REEL LTC4361CTS8-1#TRPBF LTC4361CTS8-2#TRPBF LTC4361ITS8-1#TRPBF LTC4361ITS8-2#TRPBF LTC4361CDC-1#TRPBF LTC4361CDC-2#TRPBF LTC4361IDC-1#TRPBF LTC4361IDC-2#TRPBF PART MARKING* LTDWN LTFMN LTDWN LTFMN LDWP LFMP LDWP LFMP PACKAGE DESCRIPTION 8-Lead Plastic TSOT-23 8-Lead Plastic TSOT-23 8-Lead Plastic TSOT-23 8-Lead Plastic TSOT-23 8-Lead (2mm x 2mm) Plastic DFN 8-Lead (2mm x 2mm) Plastic DFN 8-Lead (2mm x 2mm) Plastic DFN 8-Lead (2mm x 2mm) Plastic DFN TEMPERATURE RANGE 0C to 70C 0C to 70C -40C to 85C -40C to 85C 0C to 70C 0C to 70C -40C to 85C -40C to 85C
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
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LTC4361-1/LTC4361-2 ELECTRICAL CHARACTERISTICS
SYMBOL Supplies VIN VIN(UVL) IIN Thresholds VIN(OV) VOV VOC VGATE VGATE(TH) IGATE(UP) VGATE(UP) IGATE(FST) IGATE(DN) Input Pins IOUT(IN) VON(TH) ION Output Pins VGATEP(CLP) RGATEP VPWRGD(OL) RPWRGD Delay tON tOFF tPWRGD tON(OFF) GATE On Delay GATE Off Propagation Delay PWRGD Delay ON High to GATE Off VIN High to IGATE = -5A VIN = Step 5V to 6.5V VIN - VSENSE = Step 0mV to 100mV VIN = Step 5V to 6.5V VGATE > VGATE(TH) to PWRGD Low VON = Step 0V to 2.5V
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The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 5V, VON = 0V, unless otherwise noted.
PARAMETER Input Voltage Range Input Undervoltage Lockout Input Supply Current VIN Rising VON = 0V VON = 2.5V IN Pin Overvoltage Threshold Overvoltage Hysteresis Overcurrent Threshold External N-Channel MOSFET Gate Drive (VGATE - VOUT) VIN - VSENSE 2.5V VIN < 3V, IGATE = -1A 3V VIN < 5.5V, IGATE = -1A VIN Rising CONDITIONS
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MIN 2.5 1.8
TYP
MAX 80
UNITS V V A A V mV mV V V V V A V/ms mA A A A V A V M V k ms s s s ms s
2.1 220 1.5
2.45 400 10 5.916 200 55 6 7.9 6.8 7.8 -15 4.5 60 80 20 3 1.5 10 7.5 3.2 0.4 800 200 1 20 1 100 5
5.684 25 45 3.5 4.5 5.7 6.7 -5 1.5 15 10 5 0.4 2.5 5 0.8 250 50 5 25
5.8 100 50 4.5 6 6.3 7.2 -10 3 30 40 10 0 5 5.8 2 0.23 500 130 0.25 10 0.25 65 2
External Gate Drive
GATE High Threshold for PWRGD Status VIN = 3.3V VIN = 5V GATE Pull-Up Current GATE Ramp-Up GATE Pull-Down Current GATE Pull-Down Current OUT Input Current ON Input Threshold ON Pull-Down Current IN to GATEP Clamp Voltage GATEP Resistive Pull-Down PWRGD Output Low Voltage PWRGD Pull-Up Resistance to OUT VGATEP = 3V VIN = 5V, IPWRGD = 3mA VIN = 6.5V, VPWRGD = 1V VON = 2.5V VGATE = 1V VGATE = 1V to 7V Fast Turn-Off, VIN = 6V, VGATE = 9V VON = 2.5V, VGATE = 9V VOUT = 5V, VON = 0V VOUT = 5V, VON = 2.5V
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Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to GND unless otherwise specified.
Note 3: An internal clamp limits VGATE to a minimum of 4.5V above VOUT. Driving this pin to voltages beyond this clamp may damage the device.
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LTC4361-1/LTC4361-2 TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25C, VIN = 5V, VON = 0V, unless otherwise noted. Input Supply Current vs Input Voltage
10000 8 7 1000 VON = 0V IIN (A) 100 VON = 2.5V 10 VGATE (V) 6 5 4 3 2 1 1 0.1 1 10 VIN (V) 100
436112 G01
GATE Drive vs GATE Current
40
GATE Fast Pull-Down Current vs Temperature
VIN = 6V VGATE = 9V
35 IGATE(FST) (mA) VIN = 5V VIN = 3V
30
VIN = 2.5V
25
0 0 2 4 6 IGATE (A)
436112 G02
8
10
12
20 -50
-25
50 0 25 TEMPERATURE (C)
75
100
436112 G03
PWRGD Voltage vs PWRGD Current
500 8 7 400 VPWRGD(OL) (mV)
GATE Off Propagation Delay vs Overdrive
VIN = STEP 5V TO (VIN(OV) + VOVDRV) 12 11
GATE Voltage and GATE High Threshold (for PWRGD Status) vs Input Voltage
VIN = VOUT VGATE VGATE /VGGATE(TH) (V) 10 9 8 7 6 5 VGATE(TH)
6 tOFF (s) 5 4 3 2 1
300
200
100
0 0 1 3 IPWRGD (mA) 2 4 5
436112 G04
0 0 0.5 1 1.5 VOVDRV (V) 2 2.5
436012 G05
4 2.5
3
3.5
4 4.5 VIN (V)
5
5.5
6
436112 G06
Normal Start-Up Sequence
VIN 5V/DIV VOUT 5V/DIV VIN 5V/DIV VOUT 5V/DIV
GATE Slow Ramp-Up
VON 5V/DIV
Entering Sleep Mode
VOUT 5V/DIV
VGATE 10V/DIV
VGATE 10V/DIV
VGATE 10V/DIV
ICABLE 0.5A/DIV 20ms/DIV FIGURE 5 CIRCUIT RIN = 150m, LIN = 0.7H RSENSE = 25m LOAD = 10, COUT = 10F
436112 G07
ICABLE 0.5A/DIV
436112 G08
ICABLE 0.5A/DIV
1ms/DIV FIGURE 5 CIRCUIT RIN = 150m, LIN = 0.7H RSENSE = 25m LOAD = 10, COUT = 10F
50s/DIV FIGURE 5 CIRCUIT RIN = 150m, LIN = 0.7H RSENSE = 25m LOAD = 10, COUT = 10F
436112 G09
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LTC4361-1/LTC4361-2 PIN FUNCTIONS
Exposed Pad (DFN): Ground. Connection to PCB is optional. GATE: Gate Drive for External N-Channel MOSFET. An internal charge pump provides a 10A pull-up current to charge the gate of the external N-channel MOSFET. An additional ramp circuit limits the GATE ramp rate when turning on to 3V/ms. For slower ramp rates, connect an external capacitor from GATE to GND. An internal clamp limits GATE to 6V above the OUT pin voltage. An internal GATE high comparator controls the PWRGD pin. GATEP: Gate Drive for External P-Channel MOSFET. GATEP connects to the gate of an optional external P-channel MOSFET to protect against negative voltages at IN. This pin is internally clamped to 5.8V below VIN. An internal 2M resistor connects this pin to ground. Connect to IN if not used. GND: Device Ground. IN: Supply Voltage Input. Connect this pin to the input power supply. This pin has an overvoltage threshold of 5.8V. After an overvoltage event, this pin must fall below VIN(OV) - VOV to release the overvoltage lockout. During lockout, GATE is held low and the PWRGD pull-down releases. ON: On Control Input. A logic low at ON enables the LTC4361. A logic high at ON activates a low current pulldown at the GATE pin and causes the LTC4361 to enter a low current sleep mode. An internal 5A current pulls ON down to ground. Connect to ground or leave open if unused. OUT: Output Voltage Sense Input for GATE Clamp. Connect to the source of the external N-channel MOSFET to sense the output voltage for GATE to OUT clamp. PWRGD: Power Good Status. Open-drain output with internal 500k resistive pull-up to OUT. Pulls low 65ms after GATE ramps above VGATE(TH). SENSE: Current Sense Input. Connect a sense resistor between IN and SENSE. An overcurrent protection circuit turns off the N-channel MOSFET when the voltage across the sense resistor exceeds 50mV for more than 10s.
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LTC4361-1/LTC4361-2 BLOCK DIAGRAM
GATEP 200k 5.8V IN SENSE
CHARGE PUMP 10A
1.8M GATE
ON 1V 5A
+ -
OVERCURRENT COMPARATOR
GATE HIGH COMPARATOR
5.8V
+ - + - -
50mV
OUT VGATE(TH)
CONTROL
OVERVOLTAGE COMPARATOR
GND
436112 BD
6
+
500k
+
5.8V
-
5.7V
PWRGD
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LTC4361-1/LTC4361-2 OPERATION
Mobile devices like cell phones and MP3/MP4 players have highly integrated subsystems fabricated from deep submicron CMOS processes. The small form factor is accompanied by low absolute maximum voltage ratings. The sensitive electronics are susceptible to damage from transient or DC overvoltage conditions from the power supply. Failures or faults in the power adaptor can cause an overvoltage event. So can hot-plugging an AC adaptor into the power input of the mobile device (see LTC Application Note 88). Today's mobile devices derive their power supply or recharge their internal batteries from multiple alternative inputs like AC wall adaptors, car battery adaptors and USB ports. A user may unknowingly plug in the wrong adaptor, damaging the device with a high or even a negative power supply voltage. The LTC4361 protects low voltage electronics from these overvoltage conditions by controlling a low cost external N-channel MOSFET configured as a pass transistor. At power-up (VIN > 2.1V), a start-up delay cycle begins. Any overvoltage condition causes the delay cycle to continue until a safe voltage is present. When the delay cycle completes, an internal high side switch driver slowly ramps up the MOSFET gate, powering up the output at a controlled rate and limiting the inrush current to the output capacitor. If the voltage at the IN pin exceeds 5.8V (VIN(OV)), GATE is pulled low quickly to protect the load. The incoming power supply must remain below 5.7V (VIN(OV) - VOV) for the duration of the start-up delay to restart the GATE ramp-up. A sense resistor placed between IN and SENSE implements an overcurrent protection with a 50mV trip threshold and a 10s glitch filter. After an overcurrent, the LTC4361-1 latches off while the LTC4361-2 restarts following a 130ms delay. The LTC4361 has a CMOS compatible ON input. When driven low, the part is enabled. When driven high, the external N-channel MOSFET is turned off and the supply current of the LTC4361 drops to 1.5A. The PWRGD pulldown releases during this low current sleep mode, UVLO, overvoltage or overcurrent and the subsequent 130ms start-up delay. After the start-up delay, GATE starts its slow ramp-up and ramps higher than VGATE(TH) to trigger a 65ms delay cycle. When that completes, PWRGD pulls low.The LTC4361 has a GATEP pin that drives an optional external P-channel MOSFET to provide protection against negative voltages at IN.
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LTC4361-1/LTC4361-2 APPLICATIONS INFORMATION
The typical LTC4361 application protects 2.5V to 5.5V systems in portable devices from power supply overvoltage. The basic application circuit is shown in Figure 1. Device operation and external component selection is discussed in detail in the following sections.
RSENSE 0.025 M1 Si1470DH COUT 10F GATE SENSE OUT LTC4361 IN ON PWRGD GND
436112 F01
The GATE ramp rate is limited to 3V/ms. VOUT follows at a similar rate which results in an inrush current into the load capacitor COUT of: IINRUSH = COUT * dVGATE = COUT * 3 [mA/F ] dt
VIN 5V
VOUT 5V 1.5A
The servo loop is compensated by the parasitic capacitance of the external MOSFET. No further compensation components are normally required. In the case where the parasitic capacitance is less than 100pF a 100pF , compensation capacitor between GATE and ground may be required. An even slower GATE ramp and lower inrush current can be achieved by connecting an external capacitor, CG, from GATE to ground. The voltage at GATE then ramps up with a slope equal to 10A/CG [V/s]. Choose CG using the formula: CG = 10A IINRUSH * COUT
Figure 1. Protection from Input Overvoltage and Overcurrent
Start-Up When VIN is less than the undervoltage lockout level of 2.1V, the GATE driver is held low and the PWRGD pull-down is high impedance. When VIN rises above 2.1V and ON is held low, a 130ms delay cycle starts. Any undervoltage or overvoltage event at IN (VIN < 2.1V or VIN > 5.7V) restarts the delay cycle. This delay allows the N-channel MOSFET to isolate the output from any input transients that occur at start-up. When the delay cycle completes, GATE starts its slow ramp-up. GATE Control An internal charge pump enhances the external N-channel MOSFET with 6V from GATE to OUT. This allows the use of logic-level N-channel MOSFETs. An internal 6V clamp between GATE and OUT protects the MOSFET gate.
Overvoltage When power is first applied, VIN must remain below 5.7V (VIN(OV) - VOV) for more than 130ms before GATE is ramped up to turn on the MOSFET. If VIN then rises above 5.8V (VIN(OV)), the overvoltage comparator activates the 30mA fast pull-down on GATE within 1s. After an overvoltage condition, the MOSFET is held off until VIN once again remains below 5.7V for 130ms. Overcurrent The overcurrent comparator protects the MOSFET from excessive current. It trips when the SENSE pin falls more than 50mV below IN for more than 10s. When the overcurrent comparator trips, GATE is pulled low quickly and the PWRGD pull-down releases. The LTC4361-2 automatically tries to apply power again after a 130ms start-up delay.
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LTC4361-1/LTC4361-2 APPLICATIONS INFORMATION
The LTC4361-1 has an internal latch that maintains this off state until it is reset. To reset this latch, cycle IN below 2.1V (VIN(UVL)) or ON above 1.5V (VON(TH)) for more than 500s. After reset, the LTC4361-1 goes through the start-up cycle. In applications not requiring the overcurrent protection, tie the SENSE pin to the IN pin. To implement an overcurrent threshold ITRIP , choose RSENSE using the formula: RSENSE = VOC I TRIP VOC(MAX) RSENSE(MIN) VOC(MIN) RSENSE(MAX)
START-UP FROM UVLO OV RESTART FROM OV ON RESTART FROM ON OC RESTART FROM OC
PWRGD Output PWRGD is an active low output with a MOSFET pull-down to ground and a 500k resistive pull-up to OUT. The PWRGD pin pull-down releases during the low current sleep mode (invoked by ON high), UVLO, overvoltage or overcurrent and the subsequent 130ms start-up delay. After the startup delay, GATE starts its slow ramp-up and control of the PWRGD pull-down passes on to the GATE high comparator. VGATE > VGATE(TH) for more than 65ms asserts the PWRGD pull-down and VGATE < VGATE(TH) releases the pull-down. The PWRGD pull-down is capable of sinking up to 3mA of current allowing it to drive an optional LED. To interface PWRGD to another I/O rail, connect a resistor from PWRGD to the I/O rail with a resistance low enough to override the internal 500k pull-up to OUT. Figure 2 details PWRGD behavior for a LTC4361-2 with 1k pull-up to 5V at PWRGD.
After choosing the RSENSE, keep in mind that: ITRIP(MAX) = ITRIP(MIN) =
OC THRESHOLD ICABLE VIN(UVL) IN VIN(OV) VIN(OV)- VOV
OUT VGATE(TH) GATE VGATE(TH) VGATE(TH) VGATE(TH) VGATE(TH)
ON PWRGD 130ms 65ms 130ms 65ms 130ms 65ms
436112 F02
130ms
65ms
10s (NOT TO SCALE)
Figure 2. PWRGD Behavior
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LTC4361-1/LTC4361-2 APPLICATIONS INFORMATION
ON Input ON is a CMOS compatible, active low enable input. It has a default 5A pull-down to ground. Connect this pin to ground or leave open to enable normal device operation. If it is driven high while the external MOSFET is turned on, GATE is pulled low with a weak pull-down current (40A) to turn off the external MOSFET gradually, minimizing input voltage transients. The LTC4361 then goes into a low current sleep mode, drawing only 1.5A at IN. When ON goes back low, the part restarts with a 130ms delay cycle. GATEP Control GATEP has a 2M resistive pull-down to ground and a 5.8V Zener clamp in series with a 200k resistor to IN. It controls the gate of an optional external P-channel MOSFET to provide negative voltage protection. The 2M resistive pull-down turns on the MOSFET once VIN - VGATEP is more than the MOSFET gate threshold voltage. The IN to GATEP Zener protects the MOSFET from gate overvoltage by clamping its VGS to 5.8V when VIN goes high. MOSFET Configurations and Selection The LTC4361 can be used with various external MOSFET configurations (see Figure 3). The simplest configuration is a single N-channel MOSFET. It has the lowest RDS(ON) and voltage drop and is thus the most power efficient solution. When GATE is pulled to ground, the N-channel MOSFET can isolate OUT from a positive voltage at IN up to the BVDSS of the N-channel MOSFET. However, reverse current can still flow from OUT to IN via the parasitic body diode of the N-channel MOSFET. For near zero reverse-leakage current protection when GATE is pulled to ground, back-to-back N-channel MOSFETs can be used. Adding an additional P-channel MOSFET controlled by GATEP provides negative input voltage protection down to the BVDSS of the P-channel MOSFET. Another configuration consists of a P-channel MOSFET controlled by GATEP and a N-channel MOSFET controlled by GATE. This provides protection against overvoltage and negative voltage but not reverse current.
SUPPLY IN RSENSE OVERVOLTAGE PROTECTION M1 OUT GATE OVERVOLTAGE, REVERSECURRENT PROTECTION M1 M3 OUT GATE NEGATIVE VOLTAGE PROTECTION M2
SENSE
SUPPLY IN
RSENSE
SENSE
SUPPLY
RSENSE
OVERVOLTAGE, REVERSECURRENT PROTECTION M1 M3 OUT GATE
IN GATEP NEGATIVE VOLTAGE PROTECTION M2 IN GATEP
SENSE
SUPPLY
RSENSE
OVERVOLTAGE PROTECTION M1 OUT GATE
436112 F03
SENSE
Figure 3. MOSFET Configurations
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LTC4361-1/LTC4361-2 APPLICATIONS INFORMATION
WALL ADAPTOR AC/DC RIN LIN ICABLE IN MOBILE DEVICE
+
COUT CABLE LOAD
VIN 10V/DIV
ICABLE 20A/DIV
436112 F04a
5s/DIV RIN = 150m, LIN = 0.7H LOAD = 10, COUT = 10F
436112 F04b
Figure 4. 20V Hot-Plug into a 10F Capacitor
WALL ADAPTOR AC/DC
RIN
LIN ICABLE
IN
RSENSE
M1 Si1470DH
OUT
MOBILE DEVICE VIN 10V/DIV
+
GATE CABLE SENSE OUT LTC4361 IN GND
COUT LOAD VOUT 1V/DIV ICABLE 20A/DIV
436112 F05a
5s/DIV RIN = 150m, LIN = 0.7H, RSENSE = 25m LOAD = 10, COUT = 10F
436112 F05b
Figure 5. 20V Hot-Plug into the LTC4361
Input Transients Figure 4 shows a typical setup when an AC wall adaptor charges a mobile device. The inductor LIN represents the lumped equivalent inductance of the cable and the EMI filter found in some wall adaptors. RIN is the lumped equivalent resistance of the cable, adaptor output capacitor ESR and the connector contact resistance.
LIN and RIN form an LC tank circuit with any capacitance at IN. If the wall adaptor is powered up first, plugging the wall adaptor output to IN does the equivalent of applying a voltage step to this LC circuit. The resultant voltage overshoot at IN can rise to twice the DC output voltage of the wall adaptor as shown in Figure 4. Figure 5 shows the 20V adaptor output applied to the LTC4361. Due to the low capacitance at the IN pin, the plug-in transient has been brought down to a manageable level.
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LTC4361-1/LTC4361-2 APPLICATIONS INFORMATION
As the IN pin can withstand up to 80V, a high voltage Nchannel MOSFET can be used to protect the system against rugged abuse from high transient or DC voltages up to the BVDSS of the MOSFET. Figure 6 shows a 50V input plugged into the LTC4361 controlling a 60V rated MOSFET. Input transients also occur when the current through the cable inductance changes abruptly. This can happen when the LTC4361 turns off the N-channel MOSFET rapidly in an overvoltage or overcurrent event. Figure 7 shows an input transient after an overcurrent. The current in LIN will cause VIN to overshoot and avalanche the N-channel MOSFET to COUT . Typically, IN will be clamped to a voltage of VOUT + 1.3 * (BVDSS of Si1470DH) = 45V. This is well below the 85V absolute maximum voltage rating of the LTC4361. The single, nonrepetitive, pulse of energy (EAS) absorbed by the MOSFET during this avalanche breakdown with a peak current IAS is approximated by the formula: EAS = 0.5 * LIN * IAS2 For LIN = 0.7H and IAS = 4A, then EAS = 5.6J. This is within the IAS and EAS capabilities of most MOSFET's including the Si1470DH. So in most instances, the LTC4361 can ride through such transients without a bypass capacitor, transient voltage suppressor or other external components at IN. Note that if an IN bypass capacitor is used, the VIN transients will overshoot less but last longer. If VIN dips below VIN(UVL) for more than 10s, the internal latch-off latch in the LTC4361-1 could be inadvertently reset.
VIN 20V/DIV
VIN 20V/DIV VOUT 5V/DIV
VOUT 1V/DIV ICABLE 5A/DIV
436112 F06 5s/DIV FDC5612 RIN = 150m, LIN = 0.7H RSENSE = 25m, LOAD = 10, COUT = 10F
VGATE 10V/DIV ICABLE 5A/DIV
2s/DIV FIGURE 5 CIRCUIT RIN = 150m, LIN = 0.7H RSENSE = 25m, LOAD = 10, COUT = 10F
436112 F07
Figure 6. 50V Hot-Plug into the LTC4361
Figure 7. Overcurrent Turn-Off and Resulting Input Transient
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LTC4361-1/LTC4361-2 APPLICATIONS INFORMATION
Figure 8 shows a particularly severe situation which can occur in a mobile device with dual power inputs. A 20V wall adaptor is mistakenly hot-plugged into the 5V device with the USB input already live. As shown in Figure 9, a large current can build up in LIN to charge up COUT . When the N-channel MOSFET shuts off, the energy stored in LIN is dumped into COUT, causing a large 40V input transient. The LTC4361 limits this to a 1V rise in the output voltage. If the VOUT due to the discharge of the energy in LIN into COUT is not acceptable or the avalanche capability of the MOSFET is exceeded, an additional external clamp such as the SMAJ24A can be placed between IN and GND. COUT is the decoupling capacitor of the protected circuits and its value will largely be determined by their requirements. Using a larger COUT will work with LIN to slow down the dV/dt at OUT, allowing time for the LTC4361 to shut off the
RIN 20V WALL ADAPTER LIN ICABLE IN RSENSE M1 Si1470DH
MOSFET before VOUT overshoots to a dangerous voltage. A larger COUT also helps to lower the VOUT due to the discharge of the energy in LIN if the MOSFET BVDSS is used as an input clamp. Layout Considerations Figure 10 shows an example PCB layout for the LTC4361 (TS8 package) with a single N-channel MOSFET (SC70 package) and a 0603 size sense resistor. Keep the traces to the N-channel MOSFET wide and short. The PCB traces associated with the power path through the N-channel MOSFET should have low resistance. Use Kelvin connections to RSENSE for an accurate overcurrent threshold.
VIN 20V/DIV VOUT 5V/DIV OUT VGATE 10V/DIV D1 B160 GATE LTC4361 SENSE IN R1 100k OUT GND
436112 F08
+ -
COUT LOAD
ICABLE 10A/DIV
436112 F09 1s/DIV FIGURE 8 CIRCUIT RIN = 150m LIN = 2H, RSENSE = 25m, LOAD = 10 COUT = 10F (16V, SIZE 1210)
+
5V USB
-
Figure 8. Setup for Testing 20V Plugged into 5V System
Figure 9. Overvoltage Protection Waveforms When 20V Plugged into 5V System
LTC4361 GND 5 SUPPLY 6 7 8
6
5
RSENSE
Si1470DH 1 2 3
436112 F10
Figure 10. Layout for N-Channel MOSFET Configuration
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4
4
3
IN
2
1 OUT
13
LTC4361-1/LTC4361-2 PACKAGE DESCRIPTION
DC Package 8-Lead Plastic DFN (2mm x 2mm)
(Reference LTC DWG # 05-08-1719 Rev A)
0.70 0.05 2.55 0.05 1.15 0.05 0.64 0.05 (2 SIDES)
PACKAGE OUTLINE
0.25 0.45 BSC 1.37 0.05 (2 SIDES)
0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.05 TYP 2.00 0.10 (4 SIDES)
R = 0.115 TYP 5
8 0.40 0.10
PIN 1 BAR TOP MARK (SEE NOTE 6)
0.64 0.10 (2 SIDES)
PIN 1 NOTCH R = 0.20 OR 0.25 45 CHAMFER
(DC8) DFN 0106 REVO
4 0.200 REF 0.75 0.05 1.37 0.10 (2 SIDES) 0.00 - 0.05
0.23 0.45 BSC
1
0.05
BOTTOM VIEW--EXPOSED PAD
NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
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14
LTC4361-1/LTC4361-2 PACKAGE DESCRIPTION
TS8 Package 8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
2.90 BSC (NOTE 4)
0.52 MAX
0.65 REF
1.22 REF
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC
1.50 - 1.75 (NOTE 4) PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.65 BSC
0.22 - 0.36 8 PLCS (NOTE 3)
0.80 - 0.90 0.20 BSC 1.00 MAX DATUM `A' 0.01 - 0.10
0.30 - 0.50 REF
NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193
0.09 - 0.20 (NOTE 3)
1.95 BSC
TS8 TSOT-23 0802
436112f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC4361-1/LTC4361-2 TYPICAL APPLICATION
5V System Protected from 24V Power Supplies and Overcurrent 5V System Protected from 24V Power Supplies, Overcurrent and Reverse Current
M2 Si1471DH RSENSE 0.05 FDC6561AN M1 M3 COUT 10F VOUT 5V 0.5A
VIN 5V
M2
RSENSE 0.05
Si3590DV M1 COUT 10F GATE SENSE LTC4361 IN GATEP ON GND PWRGD
436112 TA02
VOUT 5V 0.5A
VIN 5V
GATE OUT VIO 5V IN R1 1k D1 LN1351CTR GATEP ON GND PWRGD
436112 TA03
SENSE LTC4361
OUT VIO 5V R1 1k D1 LN1351CTR
RELATED PARTS
PART NUMBER LTC2935 LT3008 LT3009 LTC3576/ LTC3576-1 LTC4090/ LTC4090-5 LTC4098 LTC4210 LTC4213 LT4356 LTC4411 LTC4412 LTC4413-1/ LTC4413-2 DESCRIPTION Ultralow Power Supervisor with Eight Pin-Selectable Thresholds 20mA, 45V, 3A IQ Micropower LDO 20mA, 3A IQ Micropower LDO COMMENTS 500nA Quiescent Current, 2mm x 2mm 8-Lead DFN and TSOT-23 Packages 280mV Dropout Voltage, Low IQ: 3A, VIN = 2.0V to 45V, VOUT = 0.6V to 39.5V; ThinSOT and 2mm x 2mm DFN-6 Packages 280mV Dropout Voltage, Low IQ: 3A, VIN = 1.6V to 20V, VOUT = 0.6V to 19.5V; ThinSOT and SC-70 Packages
Switching USB Power Manager with USB OTG + Triple Complete Multifunction PMIC: Bi-Directional Switching Power Manager + 3 Step-Down DC/DCs Bucks + LDO High Voltage USB Power Manager with Ideal Diode Controller and High Efficiency Li-Ion Battery Charger USB-Compatible Switchmode Power Manager with OVP Single Channel, Low Voltage Hot SwapTM Controller No RSENSETM Electronic Circuit Breaker Surge Stopper- Overvoltage/Overcurrent Protection Regulator SOT-23 Ideal Diode 2.5V to 28V, Low Loss PowerPathTM Controller in ThinSOT Dual 2.6A, 2.5V to 5.5V Fast Ideal Diodes in 3mm x 3mm DFN High Efficiency 1.2A Charger from 6V to 38V (60V Max) Input Charges Single Cell Li-Ion Batteries Directly from a USB Port High VIN: 38V operating, 60V transient; 66V OVP 1.5A Max Charge Current . from Wall, 600mA Charge Current from USB Operates from 2.7V to 16.5V, Active Current Limiting, SOT23-6 Controls Load Voltages from 0V to 6V. 3 Selectable Circuit Breaker Thresholds. Dual Level Overcurrent Fault Protection Wide Operation Range: 4V to 80V. Reverse Input Protection to -60V. Adjustable Output Clamp Voltage 2.6A Forward Current, 28mV Regulated Forward Voltage More Efficient than Diode-ORing, Automatic Switching Between DC Sources, Simplified Load Sharing 130m On Resistance, Low Reverse Leakage Current, 18mV Regulated Forward Voltage (LTC4413-2 with Overvoltage Protection Sensor)
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16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0410 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2010

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