Datasheet

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LTC1642

1642fb

Hot Swap Controller

The LTC

1642 is a 16-pin Hot Swap

controller that

allows a board to be safely inserted and removed from a

live backplane. Using an external N-Channel pass transis-

tor, the board supply voltage can be ramped up at an

adjustable rate. A high side switch driver controls the

N-Channel gate for supply voltages above 2.97V.

The SENSE pin allows foldback limiting of the load current,

with circuit breaker action after an adjustable delay time.

The delay allows the part to power-up in current limit. The

CRWBR output can be used to trigger an SCR for crowbar

protection of the load if the input supply exceeds an

adjustable threshold. The RESET output can generate a

system reset with adjustable delay when the supply

voltage falls below an adjustable threshold. The ON

pin cycles the board power. The LTC1642 is available in

the 16-pin SSOP package.

■

Adjustable Undervoltage and Overvoltage

Protection

■

Foldback Current Limit

■

Adjustable Current Limit Time-Out

■

Protected Against Surges to 33V

■

Single Channel NFET Driver

■

Latch Off or Automatic Retry on Current Fault

■

Driver for SCR Crowbar on Overvoltage

■

Adjustable Reset Timer

■

Reference Output with Uncommitted Comparator

■

16-Pin SSOP Package

■

Hot Board Insertion

■

Electronic Circuit Breaker

■

InfiniBand

Systems

1N4705

18V

12V

BACKPLANE

(SHORT PIN)

PLUG-IN CARD

SENSE GATE

GND BRK TMR

LTC1642

RST TMR

FAULT

RESET

CRWBR

COMP

–

0.33µF 0.33µF

2N2222

MCR

12DC

REF

0.1µF

2.87k

110k

100Ω

107k

13k

FDS6630A

0.01µF

0.047µF

LOAD

12V

AT 2.5A

330Ω

0.010Ω

11.3k

POWER-GOOD = 11.4V

1642 TA01

COMPOUT

GND

UV = 10.8V

OV = 13.2V

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

, LTC and LT are registered trademarks of Linear Technology Corporation. Hot Swap is

a trademark of Linear Technology Corporation. All other trademarks are the property of

their respective owners.

Summary of content (16 pages)

PAGE 1
LTC1642 Hot Swap Controller U FEATURES DESCRIPTIO ■ The LTC®1642 is a 16-pin Hot SwapTM controller that allows a board to be safely inserted and removed from a live backplane. Using an external N-Channel pass transistor, the board supply voltage can be ramped up at an adjustable rate. A high side switch driver controls the N-Channel gate for supply voltages above 2.97V.
PAGE 2
LTC1642 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) TOP VIEW Supply Voltage (VCC) .................................– 0.3V to 33V SENSE Pin ................................... – 0.3V to (VCC + 0.3V) ON, FB, OV, COMP +, COMP – RESET, FAULT, COMPOUT .....................– 0.3V to 18.5V Operating Temperature Range LTC1642C ............................................... 0°C to 70°C LTC1642I ............................................
PAGE 3
LTC1642 DC ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS ICR CRWBR Pin Current ● ● – 30 –1000 Circuit Breaker Trip Voltage ● ● 15 45 – 45 –1500 2.3 25 52.5 – 60 VCB CRWBR On, VCRWBR = 0V CRWBR On, VCRWBR = 2.1V CRWBR Off, VCRWBR = 1.
PAGE 4
LTC1642 U W TYPICAL PERFOR A CE CHARACTERISTICS GATE Pull-Down Current (Current Limit Active) IGATE Pull-Up Current vs VCC CRWBR-TMR Threshold Voltage vs Temperature 128 TA = 25°C 405 VCC = 12V CRWBR–TMR THRESHOLD VOLTAGE (mV) 25 112 96 15 80 IGATE (A) 10 64 VCC = 5V 48 32 5 0 VGATE = 0V TA = 25°C 16 0 3 6 VCC = 3.3V 9 VCC (V) 12 15 0 4 8 12 16 VGATE (V) 20 1.2 0.8 0.4 9 VCC (V) 12 1.43 1.42 1.41 1.40 1.39 1.38 –50 15 –25 OV THRESHOLD VOLTAGE (V) 1.220 1.216 1.212 1.
PAGE 5
LTC1642 U W TYPICAL PERFOR A CE CHARACTERISTICS FAULT and RESET VOL vs Temperature FAULT and RESET Pull-Up Current (IOH) vs VCC 600 160 IOL = 5mA 3.0 500 TA = 25°C 80 60 40 TA = 125°C 6 9 VCC (V) 12 VCC = 3V VCC = 5V 300 VCC = 12V 200 –25 0 25 50 75 TEMPERATURE (°C) 100 CURRENT LIMIT THRESHOLD VOLTAGE (mV) CURRENT LIMIT THRESHOLD VOLTAGE (mV) FB = 0V VCC = 15V 26.5 VCC = 12V 26.0 VCC = 5V 25.5 VCC = 3V 25.0 0 25 50 75 TEMPERATURE (°C) 100 125 125 VCC = 15V 56.0 55.
PAGE 6
LTC1642 U U U PI FU CTIO S CRWBR (Pin 1): Overvoltage Crowbar Circuit Timer and Trigger. This pin controls an external overvoltage crowbar circuit. A capacitor from the pin to ground sets a 9ms/µF delay after an overvoltage occurs until an external SCR is triggered. See Applications Information. Ground the CRWBR pin if unused. BRK TMR (Pin 2): Circuit Breaker Timer.
PAGE 7
LTC1642 U U U PI FU CTIO S OV (Pin 9): Overvoltage Input. When the voltage on OV exceeds its trip point the GATE pin is pulled low immediately and the CRWBR timer starts. If OV remains above its trip point (minus 3mV of hysteresis) long enough for CRWBR to reach its trip point, then the part turns off until reset by pulsing the ON pin low. Otherwise, the GATE pin begins ramping up one RST TMR timing cycle after OV goes below its trip point. Ground the OV pin to disable overvoltage protection.
PAGE 8
LTC1642 W BLOCK DIAGRA GATE 14 VCC 16 CRWBR 1 VCC + 21V 21V – – – 21V 1.22V + 21V + + FB 7 + 13 REF 45µA 1.5mA 25µA – SENSE 15 1.22V CHARGE PUMP 23mV TO 53mV 0.41V – VCC RISING DELAY 15µs TO 100µs 10µA AT 5V + OV 9 21V 1.22V – 5 RESET RISING DELAY 15µs TO 100µs 21V LOGIC + ON 4 21V 1.22V – VCC RISING DELAY 2µs 10µA AT 5V + VCC 2.7V – 6 FAULT RISING DELAY 10µs 21V 20µA 2µA 10 COMPOUT COMP + 11 + COMP – 12 – 21V + 21V + – 1.22V – 1.
PAGE 9
LTC1642 U U W U APPLICATIO S I FOR ATIO Hot Circuit Insertion When a circuit board is inserted into a live backplane its supply bypass capacitors can draw large currents from the backplane power bus as they charge. These currents can permanently damage connector pins and can glitch the backplane supply, resetting other boards in the system. The LTC1642 limits the charging currents drawn by a board’s capacitors, allowing safe insertion into a live backplane.
PAGE 10
LTC1642 U W U U APPLICATIO S I FOR ATIO an internal servo loop adjusts the GATE pin voltage such that Q1 acts as a constant current source. The voltage limit across R2 increases as the output charges; this foldback in the current limit helps to even out Q1’s power dissipation. The output is sensed at the FB pin. When FB is grounded, the sense voltage is limited to 26mV. When FB is greater than 0.7V, the limit is 56mV and the full dependence is shown in Figure 3.
PAGE 11
LTC1642 U U W U APPLICATIO S I FOR ATIO Automatic Restart After the Circuit Breaker Opens The LTC1642 will automatically attempt to restart itself after the circuit breaker opens if the FAULT output is tied to the ON pin. The circuit is shown in Figure 5. Diode D1 blocks the weak FAULT pull-up current source from unbalancing the R6-R5 divider.
PAGE 12
LTC1642 U U W U APPLICATIO S I FOR ATIO Overvoltage Protection The LTC1642 can protect a load from overvoltages by turning off the pass transistor if the supply voltage exceeds an adjustable limit, and by triggering a crowbar SCR if the overvoltage lasts longer than an adjustable time. The part can also be configured to automatically restart when the overvoltage clears. The overvoltage protection circuitry is shown in Figure 8.
PAGE 13
LTC1642 U W U U APPLICATIO S I FOR ATIO If there is an overvoltage, and the resistor divider feeding OV is connected to the output of the N-Channel pass transistor, the LTC1642 will automatically restart even if FAULT is not tied to ON. If the divider is connected to the input side, the LTC1642 will restart itself only if FAULT is tied to ON, and only after the overvoltage clears.
PAGE 14
LTC1642 U U W U APPLICATIO S I FOR ATIO The undervoltage monitor behaves differently if FB is above its threshold when the GATE begins ramping: RESET goes high as soon as the GATE ramp begins. RESET goes low immediately if VCC falls below the chip’s 2.5V internal undervoltage lockout threshold. To disable the undervoltage monitor, tie FB to REF and ground RESET. R2 0.015Ω VIN 12V 2.5A 16 VCC 4 ON 15 SENSE CLOAD R3 100Ω 14 R4 330Ω C2 0.047µF FB RESET VOUT + LTC1642 7 D1 1N4705 18V R9 95.
PAGE 15
LTC1642 U W U U APPLICATIO S I FOR ATIO Uncommitted Comparator Layout Considerations The uncommitted comparator has an open drain output. The comparator has 3mV of hysteresis: the output goes high when the differential input voltage exceeds 1.5mV and goes low when the differential input is less than –1.5mV. One ounce copper exhibits a sheet resistance of 530µΩ per square. To minimize self-heating, traces should be at least 0.02" wide per ampere of current and 0.03" is recommended.
PAGE 16
LTC1642 U TYPICAL APPLICATIO 12V Hot Swap Circuit for InfiniBand Modules InfiniBand BACKPLANE InfiniBand MODULE LONG R2 Q1 DC/DC CONVERTER INPUT VB_In R6 127k 1% D2 1N4705 18V 16 R5 SHORT 10.2k 1% 9 VBxEn_L 11 R4 330Ω 5% R3 100Ω R12 84.5k 1% VCC 15 14 SENSE GATE 10 COMPOUT OV COMP+ 6 4 ON REF C7 0.01µF COMP 13 C5 0.01µF CRWBR RST TMR BRK TMR 12 1 3 C6 0.1µF GND 2 C1* 0.033µF TO CONVERTER'S RUN/SS 7 FB FAULT – UV 5 RESET LTC1642 R11 12.4k 1% R9 681k 1% C2 0.