LTC4211 Hot Swap Controller with Multifunction Current Control FEATURES DESCRIPTION n The LTC®4211 is a Hot Swap™ controller that allows a board to be safely inserted and removed from a live backplane. An internal high side switch driver controls the gate of an external N-channel MOSFET for supply voltages ranging from 2.5V to 16.5V. The LTC4211 provides soft-start and inrush current limiting during the start-up period which has a programmable duration.
LTC4211 ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (VCC) ................................................17V Input Voltage FB, ON .................................................. – 0.3V to 17V SENSE, FILTER ........................... –0.3V to VCC + 0.3V TIMER ...................................................... –0.3V to 2V Output Voltage GATE ................................. Internally Limited (Note 3) RESET, FAULT ....................................... –0.
LTC4211 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS IINON ON Input Current VON = VCC or GND ILEAK RESET, FAULT Leakage Current VRESET = VFAULT = 15V, Pull-Down Device Off IINSENSE SENSE Input Current VSENSE = VCC or GND MIN l TYP MAX UNITS ±1 ±10 μA ±0.1 ±2.
LTC4211 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS tRESET Circuit Breaker Reset Delay Time ON Low to FAULT High tOFF Turn-Off Time ON Low to GATE Off Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device.
LTC4211 TYPICAL PERFORMANCE CHARACTERISTICS VGATE – VCC vs Supply Voltage GATE Voltage vs Temperature 18 30 VCC = 15V VGATE – VCC vs Temperature 18 TA = 25°C 16 16 14 14 12 12 VGATE – VCC (V) VCC = 5V 15 VCC = 3V 10 5 0 –75 –50 –25 10 8 6 2 0 2 4 4211 G08 4211 G07 GATE Output Source Current vs Supply Voltage 12 11 10 9 8 7 0 2 4 12 11 VCC = 15V 10 VCC = 12V 9 8 7 –75 –50 –25 6 8 10 12 14 16 18 20 SUPPLY VOLTAGE (V) VCC = 5V VCC = 3V 200 180 160 140 –75 –50 –25 4211 G13 200
LTC4211 TYPICAL PERFORMANCE CHARACTERISTICS Feedback Threshold vs Supply Voltage 1.250 1.245 HIGH THRESHOLD 1.240 LOW THRESHOLD 1.235 1.230 1.225 0 2 4 6 8 10 12 14 16 18 20 SUPPLY VOLTAGE (V) 1.40 VCC = 5V HIGH THRESHOLD 1.240 1.235 LOW THRESHOLD 1.230 1.20 LOW THRESHOLD 1.15 1.10 –75 –50 –25 2.0 1.9 1.8 1.7 0 2 4 9.5 9.0 8.5 8.0 2 4 2.1 2.0 1.9 1.8 1.
LTC4211 TYPICAL PERFORMANCE CHARACTERISTICS TIMER Low Threshold vs Supply Voltage TIMER High Threshold vs Temperature 1.0 1.25 1.24 1.23 1.22 1.21 1.20 –75 –50 –25 1.0 TA = 25°C 0.8 TIMER LOW THRESHOLD (V) VCC = 5V TIMER LOW THRESHOLD (V) TIMER HIGH THRESHOLD (V) 1.26 0.6 0.4 0.2 0 0 25 50 75 100 125 150 TEMPERATURE (°C) 0 2 4 2.00 1.90 1.80 1.70 4 2.1 2.0 1.9 1.8 1.7 –75 –50 –25 6 8 10 12 14 16 18 20 SUPPLY VOLTAGE (V) 6 2.
LTC4211 TYPICAL PERFORMANCE CHARACTERISTICS VCB (SLOW COMP) vs Temperature VCB (SLOW COMP) vs Supply Voltage 60 60 TA = 25°C 58 50 48 46 54 52 50 48 46 44 44 42 42 2 4 40 –75 –50 –25 6 8 10 12 14 16 18 20 SUPPLY VOLTAGE (V) 26 160 155 150 145 140 135 24 22 20 18 16 14 12 0 500 400 300 200 100 2 4 0 6 8 10 12 14 16 18 20 SUPPLY VOLTAGE (V) 4211 G40 8-PIN VERSION OR FILTER FLOATING 24 VCC = 12V 22 VCB = 0mV TO 200mV STEP 700 600 500 VCC = 3V VCC = 12V 400 300 200 VCC = 5V VCC = 15V
LTC4211 TYPICAL PERFORMANCE CHARACTERISTICS Circuit Breaker RESET Time vs Supply Voltage 200 6.0 5.0 4.5 4.0 3.5 200 CIRCUIT BREAKER RESET TIME (μs) 5.5 180 160 140 120 100 80 3.0 –75 –50 –25 0 0 25 50 75 100 125 150 TEMPERATURE (°C) 2 4.0 3.5 3.0 2.5 2.0 1.5 0 2 4 6 8 10 12 14 16 18 20 SUPPLY VOLTAGE (V) 4.5 3.0 2.5 2.0 1.5 –75 –50 –25 1.30 HIGH THRESHOLD 1.25 LOW THRESHOLD 1.20 1.15 1.
LTC4211 TYPICAL PERFORMANCE CHARACTERISTICS 0.5 TA = 25°C 0.4 0.3 0.2 0.1 0 0 2 4 GATE Overvoltage Lockout Threshold vs Temperature GATE OVERVOLTAGE LOCKOUT THRESHOLD (V) GATE OVERVOLTAGE LOCKOUT THRESHOLD (V) GATE Overvoltage Lockout Threshold vs Supply Voltage 6 8 10 12 14 16 18 20 SUPPLY VOLTAGE (V) 4211 G52 PIN FUNCTIONS 0.5 VCC = 5V 0.4 0.3 0.2 0.
LTC4211 PIN FUNCTIONS (8-Lead Package/10-Lead Package) clamps at the GATE pin determine the gate drive voltage (ΔVGATE = VGATE – VCC). The charge pump produces a minimum 4.5V of ΔVGATE for supplies in the range of 2.7V ≤ VCC < 4.75V. For 4.75V ≤ VCC ≤ 12V the ΔVGATE is limited by zener clamp Z1 connected between the GATE and VCC pins. The ΔVGATE is typically at 12V and with guaranteed minimum value of 10V. For VCC > 12V, the Zener clamp Z2 begins to set the limitation for ΔVGATE.
LTC4211 BLOCK DIAGRAM VCC 8 (9) SENSE 7 (8) GATE 6 (7) – COMP7 VCC + UVLO – + – + 50mV Z2 VZ (TYP) = 26V Z1 VZ (TYP) = 12V 0.2V 10μA CHARGE PUMP 150mV tTIMER RESET + VCC 0.
LTC4211 OPERATION COMP2 output goes high. After a glitch filter delay, RESET is pulled low (Time Point 1). When the voltage at the FB pin rises above its reset threshold (1.239V), COMP2’s output goes low and a timing cycle starts (Time Point 4). After a complete timing cycle, RESET is pulled high by the external pull-up resistor. If the FB pin rises above the reset threshold for less than a timing cycle, the RESET output remains low (Time Points 2 to 3).
LTC4211 OPERATION 250 The LTC4211’s power-on reset circuit initializes the startup procedure and ensures the chip is in the proper state if the input supply voltage is too low. If the supply voltage falls below 2.18V, the LTC4211 is in undervoltage lockout (UVLO) mode, and the GATE pin is pulled low. Since the UVLO circuitry uses hysteresis, the chip restarts after the supply voltage rises above 2.3V and the ON pin goes high.
LTC4211 OPERATION The CTIMER value is vital to ensure a proper start-up and reliable operation. A system may not start up if a timing period is set too short relative to the time needed for the output voltage to ramp up from zero to its rated value. Conversely, this timing period should not be too long as an output short can occur at start-up causing the external MOSFET to overheat. A good starting point is to set CTIMER = 10nF and adjust its value accordingly to suit the specific applications. Table 1.
LTC4211 OPERATION a start-up check to make sure the supply voltage is above its 2.3V UVLO threshold (see Time Point 1). If the input supply voltage is valid, the gate of the external pass transistor is pulled to ground by the internal 200μA current source connected at the GATE pin. The TIMER pin is held low by an internal N-channel pull-down transistor (see M6, LTC4211 Block Diagram) and the FILTER pin voltage is pulled to ground by an internal 10μA current source. Once VCC and ON (the ON pin is >1.
LTC4211 OPERATION SOFT-START WITH CURRENT LIMITING During the second timing cycle, the inrush current was described by Equation 4. Note that there is a one-to-one correspondence in the inrush current to CLOAD.
LTC4211 OPERATION FREQUENCY COMPENSATION AT SOFT-START If the external gate capacitance is greater than 600pF, no external gate capacitor is required at GATE to stabilize the internal current-limiting loop during soft-start. Otherwise, connect a gate capacitor between the GATE pin and ground to increase the total gate capacitance to be equal to or above 600pF.
LTC4211 OPERATION FAST COMPARATOR ARMED SLOW COMPARATOR ARMED CIRCUIT BREAKER TRIPS SHORT CIRCUIT RESET PULLED LOW DUE TO POWER BAD 1 2 VCC 3 4 5 6 7 8 A B C ON TIMER GATE FPD VOUT GATE VOUT POWER BAD VFB < VREF POWER GOOD VFB > VREF RESET >150mV VCC – VSENSE FAULT 300ns TYP 4211 F08 Figure 8.
LTC4211 OPERATION FAST COMPARATOR ARMED SLOW COMPARATOR ARMED CIRCUIT BREAKER TRIPS OVER CURRENT RESET PULLED LOW DUE TO POWER BAD 1 2 VCC 3 4 5 6 7 8 A B C ON TIMER GATE VOUT GATE VOUT FPD POWER BAD VFB < VREF POWER GOOD VFB > VREF RESET >50mV VCC – VSENSE VREF FILTER 2μA 10μA FAULT 4211 F09 CIRCUIT BREAKER TRIPS Figure 9.
LTC4211 OPERATION FAST COMPARATOR ARMED SLOW COMPARATOR ARMED CIRCUIT BREAKER TRIPS CIRCUIT BREAKER RESET 1 2 VCC 3 4 5 6 7 8 B 9 9A ON ON 1 ON TIMER GATE GATE VOUT FPD VFB < VREF VOUT RESET VSENSE = 50mV VCC – VSENSE REGULATING LOAD CURRENT FILTER >50mV tFAULTSC 2μA VREF 10μA FAULT 4211 F10 tRESET Figure 10.
LTC4211 OPERATION For proper circuit breaker operation, Kelvin-sense PCB connections between the sense resistor and the LTC4211’s VCC and SENSE pins are strongly recommended. The drawing in Figure 11 illustrates the correct way of making connections between the LTC4211 and the sense resistor. PCB layout should be balanced and symmetrical to minimize wiring errors.
LTC4211 OPERATION The maximum load current that trips the circuit breaker is given in Equation 12. ITRIP(MAX) = VCB(MAX) RSENSE(MIN) = 60mV RSENSE(MIN) (12) where ⎡⎢ ⎛R ⎞ ⎤⎥ RSENSE(MIN) = RSENSE(NOM) s ⎢1– ⎜ TOL ⎟ ⎥ ⎣ ⎝ 100 ⎠ ⎦ For example: If a sense resistor with 7mΩ ±5% RTOL is used for current limiting, the nominal trip current ITRIP(NOM) = 7.1A. From Equations 11 and 12, ITRIP(MIN) = 5.4A and ITRIP(MAX) = 9.02A respectively.
LTC4211 OPERATION RDS(ON). Table 5 lists some power MOSFETs that can be used with the LTC4211. For reliable circuit operation, the maximum junction temperature (TJ(MAX)) for a power MOSFET should not exceed the manufacturer’s recommended value. This includes normal mode operation, start-up, current-limit and autoretry mode in a fault condition.
LTC4211 APPLICATIONS INFORMATION BACKPLANE PCB EDGE CONNECTOR CONNECTOR (FEMALE) (MALE) LONG 5V VCC VIN 5V RSENSE 0.007Ω R1 10Ω C1 0.1μF Z1* SHORT RESET Q1 Si4410DY VOUT 5V 5A R6 10k 1 SHORT 2 RESET ON R2 10k VCC SENSE LTC4211 LONG 4 GATE GND Z1 = 1SMA10A OR SMAJ10A * OPTIONAL FB + 8 COUT 7 R4 36k 6 5 R5 15k TIMER 3 CTIMER 10nF 4211 F13 Figure 13. Hot Swap Controller On Daughter Board (Staggered Pin Connections) RSENSE 0.
LTC4211 APPLICATIONS INFORMATION BACKPLANE PCB EDGE CONNECTOR CONNECTOR (FEMALE) (MALE) RSENSE 0.007Ω LONG VCC 5V CLOAD 8 7 VCC SHORT R1 10k 6 SENSE GATE 2 M2 4 CTIMER 10nF PCB CONNECTION SENSE LONG RESET GND 3 GND μP LOGIC 1 RESET TIMER R7 10k R6 15k LTC4211 ON R2 10k R5 36k 5 FB R4 10k SHORT ON/OFF VOUT 5V 5A + RX 10Ω CX 100nF Z1* M1 Si4410DY 4211 F15 ZZ1 = 1SMA10A OR SMAJ10A M2: 2N7002LT1 * OPTIONAL Figure 15.
LTC4211 APPLICATIONS INFORMATION 12V Hot Swap Application Figure 18. In this case, the autoretry circuitry will attempt to restart the LTC4211 with a 50% duty cycle, as shown in the timing diagram of Figure 19. To prevent overheating the external MOSFET and other components during the autoretry sequence, adding a capacitor (CAUTO) to the circuit introduces an RC time constant (tOFF) that adjusts the autoretry duty cycle.
LTC4211 APPLICATIONS INFORMATION FAST COMPARATOR ARMED SLOW COMPARATOR ARMED 1 VCC 2 3 45 6 7 8 B ON/FAULT ON/FAULT tRESET TIMER GATE GATE VOUT FPD VFB < VREF VOUT RESET VSENSE = 50mV VCC – VSENSE >50mV REGULATED LOAD CURRENT VREF FILTER 10μA 2μA tOFF t1 t2 tFILTER tOFF 4211 F19 DUTY CYCLE = t2 << t1, t2 AND tOFF) (t tOFF + t1 + t2 FILTER Figure 19. Autoretry Timing To increase the RC delay, the user may either increase CAUTO or RAUTO.
LTC4211 APPLICATIONS INFORMATION BACKPLANE PCB EDGE CONNECTOR CONNECTOR (FEMALE) (MALE) 3.3V 5V OUT 3.3V OUT R8 10Ω C4 0.1μF Z1* 5V ON R9 10Ω C5 0.1μF SHORT CURRENT LIMIT: 3.3A SHORT LONG R11 10k 3 4 C1 10nF 16V VOUT1 3.3V 2A + CLOAD VOUT2 5V 2A + D2 1N4148 LTC4211 2 D3** R7 10Ω 5% Q1 1/2 Si4936DY 10k 1 R10 10k GND R2 0.015Ω 5% LONG Z2* RESET Q2 1/2 Si4936DY LONG RESET ON TIMER VCC SENSE GATE GND FB 8 7 6 CLOAD D1 R3 1N4148 10Ω 5% R6 R1 1M 10k 5% 5% R4 2.
LTC4211 APPLICATIONS INFORMATION CURRENT FLOW TO LOAD CURRENT FLOW TO LOAD POWER MOSFET (SO-8) SENSE RESISTOR (RSENSE) D G D S W W CX D S D S Z1* TRANSIENT VOLTAGE SUPPRESSOR RGX* CGX* FB GATE SENSE VIA TO GND PLANE VCC SNUBBER NETWORK RX R4 15k R3 36k NOTES: DRAWING IS NOT TO SCALE! *OPTIONAL COMPONENTS **ADDITIONAL DETAILS OMITTED FOR CLARITY GND TIMER ON RESET LTC4211** 1 CTIMER 10nF CURRENT FLOW FROM LOAD W 4211 F22 Figure 22.
LTC4211 APPLICATIONS INFORMATION SUPPLY OVERVOLTAGE DETECTION/ PROTECTION USING FILTER PIN In addition to using external protection devices around the LTC4211 for large scale transient protection, low power Zener diodes can be used with the LTC4211’s FILTER pin to act as a supply overvoltage detection/protection circuit on either the high side (input) or low side (output) of the external pass transistor. Recall that internal control circuitry keeps the LTC4211 GATE voltage from ramping up if VFILTER > 1.
LTC4211 APPLICATIONS INFORMATION IF ANY FAULT HAPPENS AFTER THIS POINT, THE CIRCUIT BREAKER TRIPS AND FAULT LATCHES LOW IF OVERVOLTAGE GOES AWAY, SECOND CYCLE CONTINUES OVERVOLTAGE 1 2 VCC 2A 3 4 5 SLOW COMPARATOR ARMED OVERVOLTAGE CIRCUIT BREAKER TRIPS, GATE PULLS DOWN AND FAULT LATCHES LOW 6 7 8 A B C ON TIMER GATE VOUT GATE VOUT FPD POWER BAD VFB < VREF POWER GOOD VFB > VREF RESET >VREF >VREF – 80mV FILTER FAULT 4211 F24 FAULT IS PULLED LOW (BUT NOT LATCHED) DUE TO A START-UP OVERVOLT
LTC4211 APPLICATIONS INFORMATION BACKPLANE PCB EDGE CONNECTOR CONNECTOR (FEMALE) (MALE) D1 IN4148 LONG 5V R3 10k R4 10Ω C1 0.1μF Z1* RSENSE 0.007Ω Q1 Si4410DY VOUT 5V 5A SHORT FAULT R5 10k SHORT RESET Z2 6.2V 1 SHORT ON/OFF 2 R6 10k R1 36k LTC4211 R7 10k 3 4 CFILTER 47pF RESET FAULT VCC ON FILTER SENSE TIMER CTIMER 5 GND 10nF GATE FB 9 8 + CLOAD 10 R2 15k 7 6 4211 F25 LONG GND Z1 = 1SMA10A OR SMAJ10A Z2 = 1N4691 * OPTIONAL Figure 25.
LTC4211 APPLICATIONS INFORMATION In either case, the LTC4211 can be configured to automatically initiate a start-up sequence. Please refer to the section on AutoRetry After a Fault for additional information. PCB Layout Considerations For proper operation of the LTC4211’s circuit breaker function, a 4-wire Kelvin connection to the sense resistors is highly recommended.
LTC4211 APPENDIX Table 4 lists some current sense resistors that can be used with the circuit breaker. Table 5 lists some power MOSFETs that are available. Table 6 lists the web sites of several manufacturers. Since this information is subject to change, please verify the part numbers with the manufacturer. Table 4. Sense Resistor Selection Guide CURRENT LIMIT VALUE PART NUMBER DESCRIPTION MANUFACTURER 1A LR120601R050 0.05Ω 0.5W 1% Resistor IRC-TT 2A LR120601R025 0.025Ω 0.
LTC4211 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660 Rev F) 3.00 p 0.102 (.118 p .004) (NOTE 3) 0.889 p 0.127 (.035 p .005) 0.254 (.010) 8 7 6 5 3.00 p 0.102 (.118 p .004) (NOTE 4) 4.90 p 0.152 (.193 p .006) DETAIL “A” 0.52 (.0205) REF 0o – 6o TYP GAUGE PLANE 5.23 (.206) MIN 1 3.20 – 3.45 (.126 – .136) 0.53 p 0.152 (.021 p .006) DETAIL “A” 0.42 p 0.038 (.
LTC4211 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661 Rev E) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 10 9 8 7 6 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0.497 ± 0.076 (.
LTC4211 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610 Rev G) .189 – .197 (4.801 – 5.004) NOTE 3 .045 t.005 .050 BSC 8 .245 MIN 7 6 5 .160 t.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) .030 t.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 w 45s (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 0s– 8s TYP .
LTC4211 REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION B 03/12 Updated Pin description information PAGE NUMBER 10, 11 Updated Figure 2 and supporting text 13 Moved Figure 7 and supporting text to page 16 and renumbered to Figure 6 16 Updated text under Second Timing (Soft-Start) Cycle 16 Replaced CGX with CGATE in Figure 6 Revised Figure 26 and supporting Low Side (Output) Overvoltage Protection text 16 32, 33 4211fb Information furnished by Linear Technology Corp
LTC4211 TYPICAL APPLICATION LOW COST OVERVOLTAGE PROTECTION There is an alternative method to implementing the overvoltage protection using a resistor divider at the FILTER pin (see Figures 27 and 28). In this implementation, the SLOW COMP is NULL in Normal Mode. Only the FAST COMP circuit breaker is available and the current limit level is 150mV/RSENSE. During the soft-cycle, the inrush current servo loop is at 50mV/RSENSE.