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LT1640L/LT1640H

1640lhfb

Negative Voltage

Hot Swap Controller

■

Allows Safe Board Insertion and Removal

from a Live – 48V Backplane

■

Operates from –10V to – 80V

■

Programmable Inrush Current

■

Programmable Electronic Circuit Breaker

■

Programmable Overvoltage Protection

■

Programmable Undervoltage Lockout

■

Power Good Control Output

The LT

1640L/LT1640H is an 8-pin, negative voltage Hot

Swap

controller that allows a board to be safely inserted

and removed from a live backplane. Inrush current is

limited to a programmable value by controlling the gate

voltage of an external N-channel pass transistor. The pass

transistor is turned off if the input voltage is less than the

programmable undervoltage threshold or greater than the

overvoltage threshold. A programmable electronic circuit

breaker protects the system against shorts. The PWRGD

(LT1640L) or PWRGD (LT1640H) signal can be used to

directly enable a power module. The LT1640L is designed

for modules with a low enable input and the LT1640H for

modules with a high enable input.

The LT1640L/LT1640H is available in 8-pin PDIP and SO

packages.

■

Central Office Switching

■

–48V Distributed Power Systems

■

Negative Power Supply Control

Hot Swap is a trademark of Linear Technology Corporation.

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

Input Inrush Current

1640 F06b

LT1640L

SENSE

†

150nF

25V

†

3.3nF

100V

0.1µF

100V

100µF

100V

IRF530

10Ω

†

18k

1N4148

†

562k

†

9.09k

†

10k

†

0.02Ω

GND

(SHORT PIN)

–48V

OV = 71V

* DIODES INC. SMAT70A

†

THESE COMPONENTS ARE APPLICATION

SPECIFIC AND MUST BE SELECTED BASED

UPON OPERATING CONDITIONS AND DESIRED

PERFORMANCE. SEE APPLICATIONS

INFORMATION.

UV = 37V

GATE DRAIN

PWRGD

1640 TA01

OUT

SENSE

TRIM

SENSE

–

OUT

–

ON/OFF

LUCENT

JW050A1-E

100µF

16V

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

INRUSH

CURRENT

1A/DIV

GATE – V

10V/DIV

DRAIN

50V/DIV

5ms/DIV

CONTACT

BOUNCE

Summary of content (16 pages)

PAGE 1
LT1640L/LT1640H Negative Voltage Hot Swap Controller U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ The LT®1640L/LT1640H is an 8-pin, negative voltage Hot SwapTM controller that allows a board to be safely inserted and removed from a live backplane. Inrush current is limited to a programmable value by controlling the gate voltage of an external N-channel pass transistor.
PAGE 2
LT1640L/LT1640H U W W W ABSOLUTE MAXIMUM RATINGS (Note 1), All Voltages Referred to VEE Supply Voltage (VDD – VEE) .................... – 0.3V to 100V DRAIN, PWRGD, PWRGD Pins ............... – 0.3V to 100V SENSE, GATE Pins .................................... – 0.3V to 20V UV, OV Pins .............................................. – 0.3V to 60V Maximum Junction Temperature ......................... 125°C Operating Temperature Range LT1640LC/LT1640HC .............................
PAGE 3
LT1640L/LT1640H ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 2), VDD = 48V, VEE = 0V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VPG Power Good Threshold VDRAIN – VEE, High to Low Transition 1.1 1.4 2.
PAGE 4
LT1640L/LT1640H U W TYPICAL PERFOR A CE CHARACTERISTICS 48 14.5 54 47 14.0 13.5 13.0 GATE PULL-UP CURRENT (µA) 55 TRIP VOLTAGE (mV) GATE VOLTAGE (V) 15.0 12.5 53 52 51 50 49 12.0 – 50 – 25 25 50 0 TEMPERATURE (°C) 75 48 – 50 100 – 25 50 0 25 TEMPERATURE (°C) 75 43 42 49 46 43 75 100 – 25 0 25 50 TEMPERATURE (°C) 75 PWRGD Output Impedance vs Temperature (LT1640H) 8 VDRAIN – VEE > 2.4V IOUT = 1mA 7 0.4 0.3 0.2 0.
PAGE 5
LT1640L/LT1640H U U U PIN FUNCTIONS UV (Pin 3): Analog Undervoltage Input. When UV is pulled below the 1.223V high to low threshold, an undervoltage condition is detected and the GATE pin will be immediately pulled low. The GATE pin will remain low until UV rises above the 1.243 low to high threshold. The UV pin is also used to reset the electronic circuit breaker.
PAGE 6
LT1640L/LT1640H TEST CIRCUIT R 5k V+ 5V PWRGD/PWRGD VDD OV VOV + – DRAIN VDRAIN LT1640L/LT1640H UV GATE VEE SENSE 48V VUV VSENSE 1640 F01 Figure 1. Test Circuit W UW TIMING DIAGRAMS 2V OV 1.223V 2V 1.203V 1.223V UV 0V 0V tPHLOV GATE 1V tPLHOV 1V tPHLUV GATE tPLHUV 1V 1640 F02 Figure 2. OV to GATE Timing SENSE 1.243V 1V 1640 F03 Figure 3. UV to GATE Timing 1.8V 50mV 1.4V DRAIN VEE tPHLSENSE GATE PWRGD 1V VEE 1640 F04 Figure 4.
PAGE 7
LT1640L/LT1640H U U W U APPLICATIONS INFORMATION Hot Circuit Insertion Power Supply Ramping When circuit boards are inserted into a live – 48V backplane, the bypass capacitors at the input of the board’s power module or switching power supply can draw huge transient currents as they charge up. The transient currents can cause permanent damage to the board’s components and cause glitches on the system power supply.
PAGE 8
LT1640L/LT1640H U U W U APPLICATIONS INFORMATION Capacitor C1 and resistor R3 prevent Q1 from momentarily turning on when the power pins first make contact. Without C1 and R3, capacitor C2 would pull the gate of Q1 up to a voltage roughly equal to VEE • C2/CGS(Q1) before the LT1640 could power up and actively pull the gate low. By placing capacitor C1 in parallel with the gate capacitance of Q1 and isolating them from C2 using resistor R3 the problem is solved.
PAGE 9
LT1640L/LT1640H U W U U APPLICATIONS INFORMATION Electronic Circuit Breaker The LT1640 features an electronic circuit breaker function that protects against short circuits or excessive supply currents. By placing a sense resistor between the VEE and SENSE pin, the circuit breaker will be tripped whenever the voltage across the sense resistor is greater than 50mV for more than 3µs as shown in Figure 7. on R7.
PAGE 10
LT1640L/LT1640H U U W U APPLICATIONS INFORMATION Under some conditions, a short circuit at the output can cause the input supply to dip below the UV threshold, resetting the circuit breaker immediately. Transistors Q2 and Q3 along with R7, R8, C4 and D1 form a programmable one-shot circuit. Before a short occurs, the GATE pin is pulled high and Q3 is turned on, pulling node 2 to VEE. Resistor R8 turns off Q2. When a short occurs, the GATE pin is pulled low and Q3 turns off.
PAGE 11
LT1640L/LT1640H U U W U APPLICATIONS INFORMATION Undervoltage and Overvoltage Detection undervoltage threshold is set to 37V and the overvoltage threshold is set to 71V. The resistor divider will also gain up the 20mV hysteresis at the UV pin and OV pin to 0.6V and 1.2V at the input respectively. The UV (Pin 3) and OV (Pin 2) pins can be used to detect undervoltage and overvoltage conditions at the power supply input.
PAGE 12
LT1640L/LT1640H U U W U APPLICATIONS INFORMATION The new threshold voltage when the input moves from low to high is:  R4 + R5  VOV = VOVH    R5   R2 • R3 + R1 • R3 + R1 • R2  VUV,LH = VUVH   R2 • R3   With R4 = 506k, R5 = 8.87k and VOVH = 1.223V, the overvoltage threshold will be 71V. where VUVH is typically 1.243V.
PAGE 13
LT1640L/LT1640H U U W U APPLICATIONS INFORMATION When the DRAIN voltage of the LT1640L is high with respect to VEE, the internal pull-down transistor Q2 is off and the PWRGD pin is in a high impedance state (Figure␣ 12). The PWRGD pin will be pulled high by the module’s internal pull-up current source, turning the module off. When the DRAIN voltage drops below VPG, Q2 will turn on and the PWRGD pin will pull low, enabling the module.
PAGE 14
LT1640L/LT1640H U PACKAGE DESCRIPTION N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) 0.400* (10.160) MAX 8 7 6 5 1 2 3 4 0.255 ± 0.015* (6.477 ± 0.381) 0.300 – 0.325 (7.620 – 8.255) 0.009 – 0.015 (0.229 – 0.381) ( +0.035 0.325 –0.015 8.255 +0.889 –0.381 ) 0.045 – 0.065 (1.143 – 1.651) 0.130 ± 0.005 (3.302 ± 0.127) 0.065 (1.651) TYP 0.100 (2.54) BSC 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003 (0.457 ± 0.
PAGE 15
LT1640L/LT1640H U PACKAGE DESCRIPTION S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.014 – 0.019 (0.355 – 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.
PAGE 16
LT1640L/LT1640H U TYPICAL APPLICATION Using an EMI Filter Module Many applications place an EMI filter module in the power path to prevent switching noise of the module from being injected back onto the power supply. A typical application using the Lucent FLTR100V10 filter module is shown in Figure 14. When using a filter, an optoisolator is required to prevent common mode transients from destroying the PWRGD and ON/OFF pins. R7 51k 5% (SHORT PIN) GND MOC207 GND R4 562k 1% R5 9.