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LT1641

1641fd

Positive High Voltage

Hot Swap Controller

The LT

1641 is an 8-pin Hot Swap

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 a program-

mable rate. A high side switch driver controls an N-channel

gate for supply voltages ranging from 9V to 80V.

The chip features a programmable analog foldback cur-

rent limit circuit. If the chip remains in current limit for

more than a programmable time, the N-channel pass

transistor turns off and is optionally set to automatically

restart after a time-out delay.

The PWRGD output indicates when the output voltage,

sensed by the FB pin, is within tolerance. The ON pin

provides programmable undervoltage lockout.

The LT1641-1/LT1641-2 are recommended for new

designs.

The LT1641 is available in the 8-lead SO package.

■

Hot Board Insertion

■

Electronic Circuit Breaker

■

Industrial High Side Switch/Circuit Breaker

■

24V/48V Industrial/Alarm Systems

■

Allows Safe Board Insertion and Removal from a

Live Backplane

■

Controls Supply Voltage from 9V to 80V

■

Programmable Analog Foldback Current Limiting

■

High Side Drive for an External N-Channel

■

Automatic Retry Capability

■

User Programmable Supply Voltage Power-Up Rate

■

Undervoltage Lockout

■

Overvoltage Protection

■

Available in 8-Lead SO Package

TIMER

SENSE GATE

CMPZ

5248B

GND

PWRGD

10Ω

49.9k

*SMAT70A

*DIODES, INC.

24V

SHORT

GND

1641 TA01

3.4k

0.68µF

0.01Ω

10nF

59k

3.57k

24k

OUT

LT1641

IRF530

24V Input Voltage Automatic Restart Application

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

Summary of content (12 pages)

PAGE 1
LT1641 Positive High Voltage Hot Swap Controller U FEATURES DESCRIPTIO ■ The LT®1641 is an 8-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 a programmable rate. A high side switch driver controls an N-channel gate for supply voltages ranging from 9V to 80V.
PAGE 2
LT1641 U W W W ABSOLUTE AXI U RATI GS (Note 1) Supply Voltage (VCC) ...............................– 0.3V to 100V Input Voltage (SENSE) .............................– 0.3V to 100V Input Voltage (TIMER) ...............................– 0.3V to 44V Input Voltage (FB, ON) ...............................– 0.3V to 60V Output Voltage (PWRGD) ........................– 0.3V to 100V Output Voltage (GATE) ............................– 0.3V to 100V Operating Temperature Range LT1641CS8 .........................
PAGE 3
LT1641 AC ELECTRICAL CHARACTERISTICS TA = 25°C, VCC = 24V SYMBOL PARAMETER CONDITIONS tPHLON ON Low to GATE Low Figures 1, 2 6 µs tPLHON ON High to GATE High Figures 1, 2 1.7 µs tPHLFB FB Low to PWRGD Low Figures 1, 3 3.2 µs tPLHFB FB High to PWRGD High Figures 1, 3 tPHLSENSE (VCC – SENSE) High to GATE Low Figures 1, 4 Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device.
PAGE 4
LT1641 U W TYPICAL PERFOR A CE CHARACTERISTICS Gate Drive vs Temperature 16 15 14 GATE DRIVE (VGATE – VCC) (V) VCC = 48V 13 12 11 10 9 8 VCC = 10.8V 7 TA = 25°C 14 12 10 8 0 25 50 TEMPERATURE (°C) 75 0 100 20 40 VCC (V) 60 TA = –45°C TA = 0°C 10 TA = 25°C TA = 85°C 6 70 90 1.330 1.325 1.320 1.315 1.310 1.305 1.300 1.295 1.290 1.285 –50 –25 0 25 50 TEMPERATURE (°C) 75 1.233 1.231 1.229 1.227 1.225 1.223 –50 0.090 75 0.080 0.070 0.
PAGE 5
LT1641 U U U PI FU CTIO S ON (Pin 1): The ON pin is used to implement undervoltage lockout. When the ON pin is pulled below the 1.233V Highto-Low threshold voltage, an undervoltage condition is detected and the GATE pin is pulled low to turn the MOSFET off. When the ON pin rises above the 1.313V Low-to-High threshold voltage, the MOSFET is turned on again. FB (Pin 2): Power Good Comparator Input. It monitors the output voltage with an external resistive divider.
PAGE 6
LT1641 W BLOCK DIAGRA VCC SENSE VP VP GEN FB – 12mV ~ 47mV CHARGE PUMP AND GATE DRIVER + + REF GEN 0.5V GATE + – PWRGD 1.233V 1.233V – + ON – VCC – 8.3V + UNDERVOLTAGE LOCKOUT LOGIC + 0.5V VP – 80µA + 1.
PAGE 7
LT1641 W UW TI I G DIAGRA S 1.313V 1.313V 1.233V ON tPLHON FB 1.233V tPLHFB tPHLON tPHLFB 1V 1V PWRGD GATE 5V 1V 1641 F03 1641 F02 Figure 2. ON to GATE Timing Figure 3. FB to PWRGD Timing VCC – SENSE 47mV tPHLSENSE VCC GATE 1641 F04 Figure 4.
PAGE 8
LT1641 U W U U APPLICATIO S I FOR ATIO RS 0.025Ω VIN 24V Q1 IRF530 SHORT PIN D1 CMPZ 5248B R5 10Ω 5% R1 49.9k 1% VOUT CL R3 59k 1% C1 R6, 10nF 1k, 5% 8 VCC 1 7 6 SENSE GATE ON R7 24k 5% FB 2 R4 3.57k 1% LT1641 R2 3.4k 1% PWRGD TIMER 3 PWRGD GND 5 GND + 4 C2 0.68µF 1641 F05 Figure 5.
PAGE 9
LT1641 U U W U APPLICATIO S I FOR ATIO VCC – VSENSE RESPONSE TIME 12µs 10µs 47mV 8µs 6µs 4µs 12mV 2µs 0V 0.5V VFB 50mV 100mV 150mV 200mV 1641 F07 Figure 7. Current Limit Sense Voltage vs Feedback Pin Voltage Automatic Restart To force the LT1641 to automatically restart after an overcurrent fault, the bottom plate of capacitor C1 can be tied back to the ON pin (Figure 10). VCC – VSENSE 1641 F08 Figure 8. Response Time to Overcurrent turning off transistor Q1.
PAGE 10
LT1641 U W U U APPLICATIO S I FOR ATIO RS 0.025Ω VIN 24V Q1 IRF530 VOUT SHORT PIN R1 49.9k 1% D1 CMPZ 5248B R5 10Ω 5% R3 59k 1% C1 10nF 8 VCC 1 7 6 SENSE GATE R7 24k 5% ON FB 2 R4 3.57k 1% LT1641 R2 3.4k 1% PWRGD TIMER 3 PWRGD GND 5 4 C2 0.68µF GND Figure 9. Short-Circuit Waveforms 1641 F10 Figure 10. Automatic Restart Application Q1 IRF530 RS 0.025Ω VIN 24V SHORT PIN R1 49.
PAGE 11
LT1641 U U W U APPLICATIO S I FOR ATIO Layout Considerations high current applications. To make the system immune to noise, the resistor divider to the ON pin needs to be close to the chip and keep traces to VCC and GND short. A 0.1µF capacitor from the ON pin to GND also helps reject induced noise. Figure 16 shows a layout that addresses these issues. To achieve accurate current sensing, a Kelvin connection is recommended. The minimum trace width for 1oz copper foil is 0.
PAGE 12
LT1641 U PACKAGE DESCRIPTIO S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 .245 MIN 7 6 5 .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) .030 ±.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 2 3 4 .053 – .069 (1.346 – 1.752) .004 – .010 (0.101 – 0.254) 0°– 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1.