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LTC4213 No RSENSETM Electronic Circuit Breaker
FEATURES

DESCRIPTIO
Fast 1s Response Circuit Breaker 3 Selectable Circuit Breaker Thresholds No Sense Resistor Required Dual Level Overcurrent Fault Protection Controls Load Voltages from 0V to 6V High Side Drive for External N-Channel FET Undervoltage Lockout READY Pin Signals When Circuit Breaker Armed Small Plastic (3mm x 2mm) DFN Package
The LTC(R)4213 is an Electronic Circuit Breaker. An overcurrent circuit breaker senses the voltage across the drain and source terminals of an external N-channel MOSFET with no need for a sense resistor. The advantages are a lower cost and reduced voltage and power loss in the switch path. An internal high-side driver controls the external MOSFET gate. Two integrated comparators provide dual level overcurrent protection over the bias supply to ground common mode range. The slow comparator has 16s response while the fast comparator trips in 1s. The circuit breaker has three selectable trip thresholds: 25mV, 50mV and 100mV. An ON pin controls the ON/OFF and resets circuit breaker faults. READY signals the MOSFET is conducting and the circuit breaker is armed. The LTC4213 operates from VCC = 2.3V to 6V.
, LTC and LT are registered trademarks of Linear Technology Corporation. No RSENSE is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.
APPLICATIO S

Electronic Circuit Breaker High-Side Switch Hot Board Insertion
TYPICAL APPLICATIO
SI4864DY
1.25V Electronic Circuit Breaker
VIN 1.25V VOUT 1.25V 3.5A
Severe Overload Response
IOUT (50A/DIV)
VBIAS 2.3V TO 6V
VCC
SENSEP GATE SENSEN VBIAS LTC4213 10k READY
VOUT (1V/DIV)
OFF ON
ON
GND
ISEL
VGATE (5V/DIV)
4213 TA01
VIN (1V/DIV)
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2s/DIV
4213 TA01b
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1
LTC4213
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW READY 1 ON 2 ISEL 3 GND 4 9 8 VCC 7 SENSEP 6 SENSEN 5 GATE
Bias Supply Voltage (VCC) ........................... -0.3V to 9V Input Voltages ON, SENSEP, SENSEN .............................- 0.3V to 9V ISEL .......................................... - 0.3V to (VCC + 0.3V) Output Voltages GATE .....................................................- 0.3V to 15V READY .....................................................- 0.3V to 9V Operating Temperature Range LTC4213C ............................................... 0C to 70C LTC4213I ............................................. -40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10sec)................... 300C
ORDER PART NUMBER LTC4213CDDB LTC4213IDDB DDB PART* MARKING LBHV
DDB PACKAGE 8-LEAD (3mm x 2mm) PLASTIC DFN TJMAX = 125C, JA = 250C/W EXPOSED PAD (PIN 9) PCB CONNECTION OPTIONAL
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V, ISEL = 0 unless otherwise noted. (Note 2)
SYMBOL VCC VSENSEP ICC VCC(UVLR) VCC(UVHYST) ISENSEP ISENSEN PARAMETER Bias Supply Voltage SENSEP Voltage VCC Supply Current VCC Undervoltage Lockout Release VCC Undervoltage Lockout Hysteresis SENSEP Input Current SENSEN Input Current VSENSEP = VSENSEN = 5V, Normal Mode VSENSEP = VSENSEN = 0, Normal Mode VSENSEP = VSENSEN = 5V, Normal Mode VSENSEP = VSENSEN = 0, Normal Mode VSENSEP = VSENSEN = 5V, Reset Mode or Fault Mode VCB Circuit Breaker Trip Voltage VCB = VSENSEP - VSENSEN Fast Circuit Breaker Trip Voltage VCB(FAST) = VSENSEP - VSENSEN GATE Pin Pull Up Current GATE Pin Pull Down Current External N-Channel Gate Drive VGS Voltage to Arm Circuit Breaker ISEL = 0, VSENSEP = VCC ISEL = Floated, VSENSEP = VCC ISEL = VCC, VSENSEP = VCC ISEL = 0, VSENSEP = VCC ISEL = Floated, VSENSEP = VCC ISEL = VCC, VSENSEP = VCC VGATE = 0V VSENSEP - VSENSEN = 200mV, VGATE = 8V VSENSEN = 0, VCC 2.97V, IGATE = -1A VSENSEN = 0, VCC = 2.3V, IGATE = -1A VSENSEN = 0, VCC 2.97V VSENSEN = 0, VCC = 2.3V

ELECTRICAL CHARACTERISTICS
CONDITIONS

MIN 2.3 0
TYP
MAX 6 6
UNITS V V mA V mV A A A A A
1.6 1.8 30 15 15 50 22.5 45 90 63 126 252 -50 10 4.8 2.65 4.4 2.5 2.07 100 40 -1 40 -1 280 25 50 100 100 175 325 -100 40 6.5 4.3 5.4 3.5
3 2.23 160 80 15 80 15
VCC Rising

27.5 55 110 115 200 371 -150 8 8 7.6 7
VCB(FAST)
IGATE(UP) IGATE(DN) VGSMAX VGSARM
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mV mV mV mV mV mV A mA V V V V
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LTC4213
ELECTRICAL CHARACTERISTICS
SYMBOL VGSMAX - VGSARM VREADY(OL) IREADY(LEAK) VON(TH) VON(HYST) VON(RST) ION(IN) VOV tOV tFAULT(SLOW) tFAULT(FAST) tDEBOUNCE tREADY tOFF tON tRESET PARAMETER Difference Between VGSMAX and VGSARM READY Pin Output Low Voltage READY Pin Leakage Current ON Pin High Threshold ON Pin Hysteresis ON Pin Reset Threshold ON Pin Input Current Overvoltage Threshold VOV = VSENSEP - VCC Overvoltage Protection Trip Time VCB Trips to GATE Discharging VCB(FAST) Trips to GATE Discharging Startup De-Bounce Time READY Delay Time Turn-Off Time Turn-On Time Reset Time
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V, ISEL = 0 unless otherwise noted. (Note 2)
CONDITIONS VSENSEN = 0, VCC 2.97V VSENSEN = 0, VCC = 2.3V IREADY = 1.6mA, Pull Down Device On VREADY = 5V, Pull Down Device Off ON Rising, GATE Pulls Up ON Falling, GATE Pulls Down ON Falling, Fault Reset, GATE Pull Down VON = 1.2V

MIN 0.3 0.15
TYP 1.1 0.8 0.2 0
MAX
UNITS V V
0.4 1 0.84 90 0.44 1 1.1 160 27 2.5 130 115 10 16 150
V A V mV V A V s s s s s s s s
0.76 10 0.36 0.41 25
0.8 40 0.4 0 0.7 65 16 1
VSENSEP = VSENSEN = Step 5V to 6.2V VSENSE Step 0mV to 50mV, VSENSEN Falling, VCC = VSENSEP = 5V VSENSE Step 0V to 0.3V, VSENSEN Falling, VSENSEP = 5V VON = 0V to 2V Step to Gate Rising, (Exiting Reset Mode) VGATE = 0V to 8V Step to READY Rising, VSENSEP = VSENSEN = 0 VON = 2V to 0.6V Step to GATE Discharging VON = 0.6V to 2V Step to GATE Rising, (Normal Mode) VON Step 2V to 0V

7
27 22 1.5 4 20
60 50 5 8 80
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
Note 2: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to ground unless otherwise specified.
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LTC4213
unless otherwise noted. ICC vs VCC
3.0 2.5 2.0 1.5 1.0 0.5 0 2.0
3.0 2.5 2.0 1.5 1.0 0.5 0 -50
TYPICAL PERFOR A CE CHARACTERISTICS
ICC vs Temperature
UNDERVOLTAGE LOCKOUT THRESHOLD (V)
BIAS SUPPLY CURRENT (mA)
BIAS SUPPLY CURRENT (mA)
2.5
3.0 3.5 4.0 4.5 5.0 BIAS SUPPLY VOLTAGE (V)
Normalized VCB vs VCC
1.06 1.04
NORMALIZED VCB
1.02 1.00 0.98 0.96 0.94 2.0
1.02 1.00 0.98 0.96 0.94 -50
NORMALIZED VCB(FAST)
NORMALIZED VCB
2.5
3.0 3.5 4.0 4.5 5.0 BIAS SUPPLY VOLTAGE (V)
Normalized VCB(FAST) vs Temperature
1.06 1.04
NORMALIZED VCB(FAST)
1.00 0.98 0.96 0.94 -50
IGATE(UP) (A)
100
IGATE(UP) (A)
1.02
-25
75 0 50 25 TEMPERATURE (C)
4
UW
5.5 6.0
4213 G01
Specifications are at TA = 25C. VCC = 5V
VCC(UVLR) vs Temperature
2.3 2.2 2.1 VCC RISING 2.0 1.9 1.8 1.7 -50 VCC FALLING
-25
75 25 0 50 TEMPERATURE (C)
100
125
-25
75 0 50 25 TEMPERATURE (C)
100
125
4213 G02
4213 G03
Normalized VCB vs Temperature
1.06 1.04 1.06 1.04 1.02 1.00 0.98 0.96
Normalized VCB(FAST) vs VCC
5.5
6.0
-25
75 0 50 25 TEMPERATURE (C)
100
125
0.94 2.0
2.5
3.0 3.5 4.0 4.5 5.0 BIAS SUPPLY VOLTAGE (V)
5.5
6.0
4213 G04
4213 G05
4213 G06
IGATE(UP) vs VCC
104 104
IGATE(UP) vs Temperature
102
102
100
98
98
100
125
96 2.0
2.5
3.0 3.5 4.0 4.5 5.0 BIAS SUPPLY VOLTAGE (V)
5.5
6.0
96 -50
-25
75 0 25 50 TEMPERATURE (C)
100
125
4213 G07
4213 G08
4213 G09
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LTC4213
unless otherwise noted.
TYPICAL PERFOR A CE CHARACTERISTICS
VGSMAX and VGSARM vs VCC
8 VGSMAX 8 VGSMAX (FOR 5VCC)
VGSMAX AND VGSARM (V)
VGSMAX AND VGSARM (V)
7 VGSARM
VGSARM (FOR 5VCC) 6 VGSMAX (FOR 2.5VCC) VGSARM (FOR 2.5VCC) 4
ON PIN THRESHOLD (V)
6
5
4
3 2.0
2.5
3.0 3.5 4.0 4.5 5.0 BIAS SUPPLY VOLTAGE (V)
VON(TH) vs Temperature
0.90 OVERVOLTAGE THRESHOLD (V)
0.85
ON PIN THRESHOLD (V)
0.72
OVERVOLTAGE THRESHOLD (V)
HIGH THRESHOLD 0.80 LOW THRESHOLD 0.75
0.70
0.65 -50
-25
75 0 50 25 TEMPERATURE (C)
tDEBOUNCE and tREADY vs VCC
100 100
tDEBOUNCE AND tREADY (s)
tDEBOUNCE AND tREADY (s)
80 tDEBOUNCE tREADY
60
60
tRESET (s)
40
20
0 2.0
2.5
3.0 3.5 4.0 4.5 5.0 BIAS SUPPLY VOLTAGE (V)
UW
5.5
4213 G10
Specifications are at TA = 25C. VCC = 5V
VGSMAX and VGSARM vs Temperature
0.90
VON(TH) vs VCC
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0.85 HIGH THRESHOLD 0.80 LOW THRESHOLD 0.75
5
0.70
6.0
3 -50
-25
75 0 25 50 TEMPERATURE (C)
100
125
0.65 2.0
2.5
3.0 3.5 4.0 4.5 5.0 BIAS SUPPLY VOLTAGE (V)
5.5
6.0
4213 G11
4213 G12
VOV vs VCC
0.74 1.0 0.9 0.8 0.7 0.6 0.5
VOV vs Temperature
0.70
0.68
100
125
0.66 2.0
2.5
3.0 3.5 4.0 4.5 5.0 BIAS SUPPLY VOLTAGE (V)
5.5
6.0
0.4 -50
-25
75 0 25 50 TEMPERATURE (C)
100
125
4213 G13
4213 G14
4213 G15
tDEBOUNCE and tREADY vs Temperature
120 100 80 60 40 20 20
tRESET vs VCC
80 tDEBOUNCE
40
tREADY
5.5
6.0
0 -50
-25
75 0 50 25 TEMPERATURE (C)
100
125
0 2.0
2.5
3.0 3.5 4.0 4.5 5.0 BIAS SUPPLY VOLTAGE (V)
5.5
6.0
4213 G16
4213 G17
4213 G18
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LTC4213
unless otherwise noted.
TYPICAL PERFOR A CE CHARACTERISTICS
tRESET vs Temperature
100 22 20 90
tFAULT(SLOW) (s)
18 16 14 12
tFAULT(SLOW) (s)
tRESET (s)
80
70 12 10 -50
60 -50
-25
75 0 50 25 TEMPERATURE (C)
tFAULT(FAST) vs VCC
1.3 1.2 1.3 1.2
tFAULT(FAST) (s)
1.0 0.9 0.8 0.7 2.0
tFAULT(FAST) (s)
1.1
2.5
3.0 3.5 4.0 4.5 5.0 BIAS SUPPLY VOLTAGE (V)
6
UW
100 125
4213 G19
Specifications are at TA = 25C. VCC = 5V
tFAULT(SLOW) vs VCC
22 20 18 16 14
tFAULT(SLOW) vs Temperature
10 2.0
2.5
3.0 3.5 4.0 4.5 5.0 BIAS SUPPLY VOLTAGE (V)
5.5
6.0
-25
75 0 50 25 TEMPERATURE (C)
100
125
4213 G20
4213 G21
tFAULT(FAST) vs Temperature
1.1 1.0 0.9 0.8 0.7 -50
5.5
6.0
-25
75 0 25 50 TEMPERATURE (C)
100
125
4213 G22
4213 G23
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LTC4213
PI FU CTIO S
READY (Pin 1): READY Status Output. Open drain output that goes high impedance when the external MOSFET is on and the circuit breaker is armed. Otherwise this pin pulls low. ON (Pin 2): ON Control Input. The LTC4213 is in reset mode when the ON pin is below 0.4V. When the ON pin increases above 0.8V, the device starts up and the GATE pulls up with a 100A current source. When the ON pin drops below 0.76V, the GATE pulls down. To reset a circuit breaker fault, the ON pin must go below 0.4V. ISEL (Pin 3): Threshold Select Input. With the ISEL pin grounded, float or tied to VCC the VCB is set to 25mV, 50mV or 100mV, respectively. The corresponding VCB(FAST) values are 100mV, 175mV and 325mV. GND (Pin 4): Device Ground. GATE (Pin 5): GATE Drive Output. An internal charge pump supplies 100A pull-up current to the gate of the external N-channel MOSFET. Internal circuitry limits the voltage between the GATE and SENSEN pins to a safe gate drive voltage of less than 8V. When the circuit breaker trips, the GATE pin abruptly pulls to GND. SENSEN (Pin 6): Circuit Breaker Negative Sense Input. Connect this pin to the source of the external MOSFET. During reset or fault mode, the SENSEN pin discharges the output to ground with 280A. SENSEP (Pin 7): Circuit Breaker Positive Sense Input. Connect this pin to the drain of external N-channel MOSFET. The circuit breaker trips when the voltage across SENSEP and SENSEN exceeds VCB. The input common mode range of the circuit breaker is from ground to VCC + 0.2V when VCC < 2.5V. For VCC 2.5V, the input common mode range is from ground to VCC + 0.4V. VCC (Pin 8): Bias Supply Voltage Input. Normal operation is between 2.3V and 6V. An internal under-voltage lockout circuit disables the device when VCC < 2.07V. Exposed Pad (Pin 9): Exposed pad may be left open or connected to device ground.
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LTC4213
BLOCK DIAGRA
ISEL 3 VCB VCB(FAST) 100mV 325mV 50mV 175mV 25mV 100mV
SENSEP
SLOWCOMP
FASTCOMP 280A
OVCOMP CHARGE PUMP
READY 1
16s DELAY CB TRIPS
1s DELAY CB TRIPS
RESET OR FAULT MODE
65s DELAY BLANK OV TRIPS GATE ON
50s DELAY RESET
LOGIC
STARTUP
NORMAL MODE GATE ON/OFF 8s 5s DELAY GATEOFF
80s DELAY
60s DELAY
-
COMP1
+
+
UV COMP
-
+
COMP2
-
0.4V
VCC 2
2.07V ON
0.8V 4 GND
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8
-
+
-
+
-
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7 VCB 6 SENSEN 8 VCC
+ - +
VCB(FAST)
+ -
+ -
0.7V VCC VCC
100A GATE 5
+
ARM ARM COMP
6.5V CLAMP CIRCUIT
-
+-
VGSARM SENSEN
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LTC4213
TI I G DIAGRA
VON(TH)
VON
VGATE
VSENSE
VGATE
VON
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1 2 3 4 VON(TH) VON(TH) - VON(HYST) 5 6 VGSMAX VGSMAX - 0.3V 0.3V 0.3V tDEBOUNCE tOFF tON 1 1.2V 2 3 4 5 VGSMAX VGSMAX - 0.3V 0.3V VON(TH) VON(RST)
4213 TD
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tFAULT(FAST)
tRESET
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LTC4213
OPERATIO
Overview
The LTC4213 is an Electronic Circuit Breaker (ECB) that senses load current with the the RDSON of the external MOSFET instead of using an external sense resistor. This no RSENSE method is less precise than RSENSE method due to the variation of RDSON. However, the advantages are less complex, lower cost and reduce voltage and power loss in the switch path owing to the absence of a sense resistor. Without the external sense resistor voltage drop, the VOUT improvement can be quite significant especially in the low voltage applications. The LTC4213 is designed to operate over a bias supply range from 2.3V to 6V. When bias supply voltage and the ON pin are sufficiently high, the GATE pin starts charging after an internal debounce delay of 60s. During the GATE ramp-up, the circuit breaker is not armed until the external MOSFET is fully turned on. Once the circuit breaker is armed, the LTC4213 monitors the load current through the RDSON of the external MOSFET. Circuit Breaker Function The LTC4213 provides dual level and dual response time circuit breaker functions for overcurrent protection. The LTC4213 circuit breaker function block consists of two comparators, SLOWCOMP and FASTCOMP. The
APPLICATIO S I FOR ATIO
Figure 1 shows an electronic circuit breaker (ECB) application. An external auxiliary supply biases the VCC pin and the internal circuitry. A VIN load supply powers the load via an external MOSFET. The SENSEP and SENSEN pins
VIN 1.25V CIN 100F Q1 SI4864DY VOUT 1.25V 3.5A
+
CLOAD 100F
VBIAS 2.5V
VCC SENSEP GATE SENSEN C1 0.1F ON LTC4213 GND ISEL READY
R4 10k
OFF ON
Figure 1. LTC4213 Electronic Circuit Breaker Application
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thresholds of SLOWCOMP and FASTCOMP are VCB and VCB(FAST). The ISEL pin selects one of the three settings: 1. VCB = 25mV and VCB(FAST) = 100mV with ISEL at GND 2. VCB = 50mV and VCB(FAST) = 175mV with ISEL floating 3. VCB = 100mV and VCB(FAST) = 325mV with ISEL at VCC ISEL can be stepped dynamically, such as to allow a higher circuit breaker threshold at startup and a lower threshold after supply current has settled. The inputs of the comparators are SENSEP and SENSEN pins. The voltage across the drain and source of the external MOSFET is sensed at SENSEP and SENSEN. VSENSE = VSENSEP - VSENSEN (1) When VSENSE exceeds the VCB threshold but is less than VCB(FAST), the comparator SLOWCOMP trips the circuit breaker after a 16s delay. If VSENSE is greater than VCB(FAST), the comparator FASTCOMP trips the circuit breaker in 1s. A severe short circuit condition can cause the load supply to dip substantially. This does not pose a problem for the LTC4213 as the input stages of the current limit comparators are common mode to ground. sense the load current at the drain and source of the external MOSFET. In ECB applications, large input bypass capacitors are usually recommended for good transient performance. Undervoltage Lockout An internal undervoltage lockout (UVLO) circuit resets the LTC4213 if the VCC supply is too low for normal operation. The UVLO comparator (UVCOMP) has a low-to-high threshold of 2.07V and 100mV of hysteresis. UVLO shares the glitch filters for both low-to-high transition (startup) and high-to-low transition (reset) with the ON pin comparators. Above 2.07V bias supply voltage, the LTC4213 starts if the ON pin conditions are met. Short, shallow bus bias
+
VCC
4213 F01
LTC4213
APPLICATIO S I FOR ATIO
supply transient dips below 1.97V of less than 80s are ignored. ON Function When VON is below comparator COMP1's threshold of 0.4V for 80s, the device resets. The system leaves reset mode if the ON pin rises above comparator COMP2's threshold of 0.8V and the UVLO condition is met. Leaving reset mode, the GATE pin starts up after a tDEBOUNCE delay of 60s. When ON goes below 0.76V, the GATE shuts off after a 5s glitch filter delay. The output is discharged by the external load when VON is in between 0.4V to 0.8V. At this state, the ON pin can re-enable the GATE if VON exceeds 0.8V for more than 8s. Alternatively, the device resets if the ON pin is brought below 0.4V for 80s. Once reset, the GATE pin restarts only after the tDEBOUNCE 60s delay at VON rising above 0.8V. To protect the ON pin from overvoltage stress due to supply transients, a series resistor of greater than 10k is recommended when the ON pin is connected directly to the supply. An external resistive divider at the ON pin can be used with COMP2 to set a supply undervoltage lockout value higher than the internal UVLO circuit. An RC filter can be implemented at the ON pin to increase the powerup delay time beyond the internal 60s delay. Gate Function The GATE pin is held low in reset mode. 60s after leaving reset mode, the GATE pin is charged up by an internal 100A current source. The circuit breaker arms when VGATE > VSENSEN + VGSARM. In normal mode operation, the GATE peak voltage is internally clamped to VGSMAX above the SENSEN pin. When the circuit breaker trips, an internal MOSFET shorts the GATE pin to GND, turning off the external MOSFET. READY Status The READY pin is held low during reset and at startup. It is pulled high by an external pullup resistor 50s after the circuit breaker arms. The READY pin pulls low if the circuit breaker trips or the ON pin is pulled below 0.76V, or VCC drops below undervoltage lockout.
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VGSARM and VGSMAX Each MOSFET has a recommended VGS drive voltage where the channel is deemed fully enhanced and RDSON is minimized. Driving beyond this recommended VGS voltage yields a marginal decrease in RDSON. At startup, the gate voltage starts at ground potential. The GATE ramps past the MOSFET threshold and the load current begins to flow. When VGS exceeds VGSARM, the circuit breaker is armed and enabled. The chosen MOSFET should have a recommended minimum VGS drive level that is lower than VGSARM. Finally, VGS reaches a maximum at VGSMAX. Trip and Reset Circuit Breaker Figure 2 shows the timing diagram of VGATE and VREADY after a fault condition. A tripped circuit breaker can be reset either by cycling the VCC bias supply below UVLO threshold or pulling ON below 0.4V for >tRESET. Figure 3 shows the timing diagram for a tripped circuit breaker being reset by the ON pin. Calculating Current Limit The fault current limit is determined by the RDSON of the MOSFET and the circuit breaker voltage VCB.
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ILIMIT =
VCB RDSON
(2)
The RDSON value depends on the manufacturer's distribution, VGS and junction temperature. Short Kelvin-sense connections between the MOSFET drain and source to the LTC4213 SENSEP and SENSEN pins are strongly recommended. For a selected MOSFET, the nominal load limit current is given by:
ILIMIT (NOM) =
VCB(NOM) RDSON(NOM)
(3)
The minimum load limit current is given by:
ILIMIT (MIN) = VCB(MIN) RDSON(MAX) (4)
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LTC4213
APPLICATIO S I FOR ATIO
The maximum load limit current is given by:
ILIMIT (MAX) =
VCB(MAX) RDSON(MIN)
Most MOSFET data sheets have an RDSON specification with typical and maximum values but no minimum value. Assuming a normal distribution with typical as mean, the minimum value can be estimated as
RDSON(MIN) = 2 * RDSON(NOM) - RDSON(MAX) (6)
The LTC4213 gives higher gate drive than the manufacturer specified gate drive for RDSON. This gives a slightly lower RDSON than specified. Operating temperature also modulates the RDSON value.
SHORT CIRCUIT A >VCB B
VSENSE
VGATE
VREADY
Figure 2. Short Circuit Fault Timing Diagram
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Example Current Limit Calculation
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(5)
An Si4410DY is used for current detection in a 5V supply system with the LTC4213 VCB at 25mV (ISEL pin grounded). The RDSON distribution for the Si4410DY is Typical RDSON = 0.015 = 100% Maximum RDSON = 0.02 = 133.3% Estimated MIN RDSON = 2 * 15 - 20 = 0.010 = 66.7% The RDSON variation due to gate drive is RDSON @ 4.5VGS = 0.015 = 100% (spec. TYP) RDSON @ 4.8VGS = 0.014 = 93% (MIN VGSMAX) RDSON @ 7VGS = 0.0123 = 82% (NOM VGSMAX) RDSON @ 8VGS = 0.012 = 80% (MAX VGSMAX)
CIRCUIT BREAKER TRIPS GATE AND READY PINS PULL LOW
VCB
CB TRIPS
tFAULT
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LTC4213
APPLICATIO S I FOR ATIO
CIRCUIT BREAKER TRIPS GATE AND READY PINS PULL LOW SHORT CIRCUIT NOT RESET 1 2 3 4 5
VCC > 2.07V VON 0.8V 0.76V 0.4V 0V
>VCB VCB VSENSE tFAULT
CB TRIPS VGATE
VREADY
NORMAL MODE
Figure 3. Resetting Fault Timing Diagram
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RESET REINITIALIZE RESTART 67 8 VON < 0.4V DURATION > tRESET FAULT LATCHED OFF tDEBOUNCE STARTUP CYCLE
4213 F03
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LTC4213
APPLICATIO S I FOR ATIO
Operating temperature of 0 to 70C. RDSON @ 25C = 100% RDSON @ 0C = 90% RDSON @ 70C = 120% MOSFET resistance variation: RDSON(NOM) = 15m * 0.82 = 12.3m
RDSON(MAX) = 15m * 1.333 * 0.93 * 1.2 = 15m * 1.488 = 22.3m RDSON(MIN) = 15m * 0.667 * 0.80 * 0.90 = 15m * 0.480 = 7.2m VCB variation: NOM VCB = 25mV = 100% MIN VCB = 22.5mV = 90% MAX VCB = 27.5mV = 110% The current limits are: ILIMIT(NOM) = 25mV/12.3m = 2.03A ILIMIT(MIN) = 22.5mV/22.3m = 1.01A ILIMIT(MAX) = 27.5mV/7.2m = 3.82A For proper operation, the minimum current limit must exceed the circuit maximum operating load current with margin. So this system is suitable for operating load current up to 1A. From this calculation, we can start with the general rule for MOSFET RDSON by assuming maximum operating load current is roughly half of the ILIMIT(NOM). Equation 7 shows the rule of thumb.
IOPMAX = VCB(NOM) 2 * RDSON(NOM) (7)
Note that the RDSON(NOM) is at the LTC4213 nominal operating VGSMAX rather than at typical vendor spec. Table 1 gives the nominal operating VGSMAX at the various operating VCC. From this table users can refer to the MOSFET's data sheet to obtain the RDSON(NOM) value.
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Table 1. Nominal Operating VGSMAX for Typical Bias Supply Voltage
VCC (V) 2.3 2.5 2.7 3.0 3.3 5.0 6.0 VGSMAX (V) 4.3 5.0 5.6 6.5 7.0 7.0 7.0
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Load Supply Power-Up after Circuit Breaker Armed Figure 4 shows a normal power-up sequence for the circuit in Figure 1 where the VIN load supply power-up after circuit breaker is armed. VCC is first powered up by an auxiliary bias supply. VCC rises above 2.07V at time point 1. VON exceeds 0.8V at time point 2. After a 60s debounce delay, the GATE pin starts ramping up at time point 3. The external MOSFET starts conducting at time point 4. At time point 5, VGATE exceed VGSARM and the circuit breaker is armed. After 50s (tREADY delay), READY pulls high by an external resistor at time point 6. READY signals the VIN load supply module to start its ramp. The load supply begins soft-start ramp at time point 7. The load supply ramp rate must be slow to prevent circuit breaker tripping as in equation (8).
VIN IOPMAX - ILOAD < t C LOAD (8)
Where IOPMAX is the maximum operating current defined by equation 7. For illustration, VCB = 25mV and RDSON = 3.5m at the nominal operating VGSMAX. The maximum operating current is 3.5A (refer to equation 7). Assuming the load can draw a current of 2A at power-up, there is a margin of 1.5A available for CLOAD of 100F and VIN ramp rate should be <15V/ms. At time point 8, the current through the MOSFET reduces after CLOAD is fully charged.
4213f
LTC4213
APPLICATIO S I FOR ATIO
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3
2.07V 0.8V VCC, VON VGSMAX + VSENSEN
VGATE
Vth
VSENSEP, VSENSEN
VREADY
VSENSE
RESET MODE
tDEBOUNCE
Figure 4. Load Supply Power-Up After Circuit Breaker Armed
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CIRCUIT BREAKER ARMS 4 5 67 8 VGSMAX VGSARM 100A VCB STARTUP CYCLE tREADY NORMAL CYCLE
4213 F04
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LTC4213
APPLICATIO S I FOR ATIO
Load Supply Power-Up Before VCC
Referring back to Figure 1, the VIN load supply can also be powered up before VCC. Figure 5 shows the timing diagram with the VIN load supply active initially. An internal circuit ensures that the GATE pin is held low. At time point 1, VCC clears UVLO and at time point 2, ON clears 0.8V. 60s later at time point 3, the GATE is ramped up with 100A. At time point 4, GATE reaches the external MOSFET threshold VTH and VOUT starts to ramp up. At time point 5, VSENSEN is near its peak. At time point 6, the circuit breaker is armed and the circuit breaker can trip if VSENSE > VCB.
0
1
2
VCC > 2.07V VON > 0.8V VCC, VON VGSMAX + VSENSEN VGSARM + VSENSEN
VGATE
VSENSEP
VSENSEN
VREADY tREADY RESET MODE tDEBOUNCE STARTUP CYCLE NORMAL CYCLE
4213 F05
Figure 5. Load Supply Power-Up Before VCC
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At time point 7, the GATE voltage peaks. 50s after time point 6, READY goes HIGH. Startup Problems There is no current limit monitoring during output charging for the figure 5 power-up sequence where the load supply is powered up before VCC. This is because the GATE voltage is below VGSARM and the MOSFET may not reach the specified RDSON. The VIN load supply should have sufficient capability to handle the inrush as the output charges up. For proper startup, the final load at time
CIRCUIT BREAKER ARMS VSENSEP - VSENSEN = VCB VGATE MAXES OUT READY SIGNALS 3 4 5 6 7 8 Vth
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LTC4213
APPLICATIO S I FOR ATIO
point 6 should be within the circuit breaker limits. Otherwise, the system fails to start and the circuit breaker trips immediately after arming. In most applications additional external gate capacitance is not required unless CLOAD is large and startup becomes problematic. If an external gate capacitor is employed, its capacitance value should not be excessive unless it is used with a series resistor. This is because a big gate capacitor without resistor slows down the GATE turn off during a fault. An alternative method would be a stepped ISEL pin to allow a higher current limit during startup. In the event of output short circuit or a severe overload, the load supply can collapse during GATE ramp up due to load supply current limit. The chosen MOSFET must withstand this possible brief short circuit condition before time point 6 where the circuit breaker is allowed to trip. Bench short circuit evaluation is a practical verification of a reliable design. To have current limit while powering a MOSFET into short circuit conditions, it is preferred that the load supply sequences to turn on after the circuit breaker is armed as described in an earlier section. Power-Off Cycle The system can be powered off by toggling the ON pin low. When ON is brought below 0.76V for 5s, the GATE and READY pins are pulled low. The system resets when ON is brought below 0.4V for 80s. MOSFET Selection The LTC4213 is designed to be used with logic (5V) and sub-logic (3V) MOSFETs for VCC potentials above 2.97V with VGSMAX exceeding 4.5V. For a VCC supply range between 2.3V and 2.97V, sub-logic MOSFETs should be used as the minimum VGSMAX is less than 4.5V.
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The selected MOSFET VGS absolute maximum rating should meet the LTC4213 maximum VGSMAX of 8V. Other MOSFET criteria such as VBDSS, IDMAX, and RDSON should be reviewed. Spikes and ringing above maximum operating voltage should be considered when choosing VBDSS. IDMAX should be greater than the current limit. The maximum operating load current is determined by the RDSON value. See the section on "Calculating Current Limit" for details. Supply Requirements The LTC4213 can be powered from a single supply or dual supply system. The load supply is connected to the SENSEP pin and the drain of the external MOSFET. In the single supply case, the VCC pin is connected to the load supply, preferably with an RC filter. With dual supplies, VCC is connected to an auxiliary bias supply VAUX where VAUX voltage should be greater or equal to the load supply voltage. The load supply voltage must be capable of sourcing more current than the circuit breaker limit. If the load supply current limit is below the circuit breaker trip current, the LTC4213 may not react when the output overloads. Furthermore, output overloads may trigger UVLO if the load supply has foldback current limit in a single supply system. VIN Transient and Overvoltage Protection Input transient spikes are commonly observed whenever the LTC4213 responds to overload. These spikes can be large in amplitude, especially given that large decoupling capacitors are absent in hot swap environments. These short spikes can be clipped with a transient suppressor of adequate voltage and power rating. In addition, the LTC4213 can detect a prolonged overvoltage condition. When
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LTC4213
APPLICATIO S I FOR ATIO
SENSEP exceeds VCC + 0.7V for more than 65s, the LTC4213's internal overvoltage protection circuit activates and the GATE pin pulls down and turns off the external MOSFET. Typical Electronic Fuse Application for a Single Supply System Figure 6 shows a single supply electronic fuse application. An RC filter at VCC pin filters out transient spikes. An optional Schottky diode can be added if severe VCC dips during a fault start-up condition is a concern. The use of the Schottky and RC filter combination is allowed if the load supply is above 2.9V and the total voltage drop towards the VCC pin is less than 0.4V. The LTC4213's internal UVLO filter further rejects bias supply's transients of less than tRESET. During power-up, it is good engineering practice to ensure that VCC is fully established before the ON pin enables the system at VON = 0.8V. In this application, the VCC voltage reached final value approximately after a 5.3 * R1 C1 delay. This is followed by the ON pin exceeding 0.8V after a 0.17 * R2C2 delay. The GATE pin starts up after an internal tDEBOUNCE delay.
VIN 5V CIN 100F
+
R1 33 R3 324k C1 10F
Q2 2N7002 RESET R2 80.6k
Figure 6. Single Supply Electronic Fuse
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Typical Single Supply Hot SwapTM Application A typical single supply Hot Swap application is shown in Figure 7. The RESET signal at the backplane is held low initially. When the PCB long edge makes contact the ON pin is held low (<0.4V) and the LTC4213 is kept in reset mode. When the short edge makes contact the VIN load supply is connected to the card. The VCC is biased via the RC filter. The VOUT is pre-charged via R5. To power-up successfully, the R5 resistor value should be small enough to provide the load requirement and to overcome the 280A current source sinking into the SENSEN pin. On the other hand, the R5 resistor value should be big enough avoiding big inrush current and preventing big short circuit current. When RESET signals high at backplane, C2 capacitor at the ON pin charges up via the R3/R2 resistive divider. When ON pin voltage exceeds 0.8V, the GATE pin begins to ramp up. When the GATE voltage peaks, the external MOSFET is fully turned on and the VIN-to-VOUT voltage drop reduces. In normal mode operation, the LTC4213 monitors the load current through the RDSON of the external MOSFET.
Hot Swap is a trademark of Linear Technology Corporation. Q1 SI4410DY D1 MBRO520L CLOAD 100F
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VOUT 5V 1A
VCC SENSEP GATE SENSEN LTC4213 ON C2 0.22F GND ISEL READY R4 10k
VIN
4213 F06
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LTC4213
PACKAGE DESCRIPTIO U
DDB Package 8-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1702)
0.61 0.05 (2 SIDES) 0.675 0.05 2.50 0.05 1.15 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.20 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229 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 PIN 1 BAR TOP MARK (SEE NOTE 6) 2.00 0.10 (2 SIDES) 3.00 0.10 (2 SIDES) R = 0.115 TYP 5 0.56 0.05 (2 SIDES) 0.38 0.10 8 0.200 REF 0.75 0.05 4 0.25 0.05 2.15 0.05 (2 SIDES) BOTTOM VIEW--EXPOSED PAD 1 PIN 1 CHAMFER OF EXPOSED PAD
(DDB8) DFN 1103
0.50 BSC
0 - 0.05
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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.
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LTC4213
TYPICAL APPLICATIO
STAGGERED PCB EDGE CONNECTOR VIN 3.3V Zx SMAJ6.0A D1 BAT54ALT1 RESET R1 68 R2 80.6k C2 1F VCC ISEL NC ON
BACKPLANE GND
RELATED PARTS
PART NUMBER LTC1421 LTC1422 LTC1642 LTC1645 LTC1647 LTC4210 LTC4211 LTC4216 LTC4221 LTC4230 LTC4251 LTC4252 LTC4253 DESCRIPTION Dual Channel, Hot SwapTM Controller Single Channel, Hot Swap Controller in SO-8 Fault Protected, Hot Swap Controller Dual Channel Hot Swap Controller Dual Channel, Hot Swap Controller Single Channel, Hot Swap Controller in SOT-23 Single Channel, Hot Swap Controller in MSOP Ultra Low Voltage Hot Swap Controller Dual Channel, Hot Swap Controller Triple Channel, Hot Swap Controller -48V Hot Swap Controller in S0T-23 -48V Hot Swap Controller in MSOP -48V Hot Swap Controller and Sequencer COMMENTS 24-Pin, Operates from 3V to 12V and Supports -12V Operates from 2.7V to 12V, System Reset Output Operates up to 16.5V, Overvoltage Protection to 33V 3.3V, 5V and 12V Supplies Operates from 1.2V to 12V, Power Sequencing Operates from 2.7V to 16.5V Operates from 2.7V to 16.5V, Multifunction Current Control 2.5V to 16.5V, Multifunction Current Control Operates from 2.7V to 16.5V, Multifunction Current Protects Load Voltages from 0V to 6V 1.7V to 16.5V, Multifunction Current Control -48V Hot Swap Controller, Active Current Limiting Active Current Limiting with Drain Acceleration Active Current Limiting with Drain Acceleration and Three Sequenced Power Good Outputs
LTC1643AL/LTC1643AH PCI Hot Swap Controllers
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
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VIN Q1 IRF7455 R3 182k R5 330 VOUT 3.3V 3.6A
+
CLOAD 100F
SENSEP GATE
SENSEN R4 10k READY GND
LTC4213
C1 2.2F
4213 TA02
CARD GND
Figure 7. Single Supply Hot Board Insertion
4213f LT/TP 0405 500 * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2005

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