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LT4250L/LT4250H

4250lhfa

TYPICAL APPLICATION

DESCRIPTION

Negative 48V

Hot Swap Controller

Voltage Step on Input Supply

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

trademark of Linear Technology Corporation.

FEATURES

APPLICATIONS

Allows Safe Board Insertion and Removal from a

Live –48V Backplane

Circuit Breaker Immunity to Voltage Steps and

Current Spikes

Programmable Inrush and Short-Circuit Current

Limits

Pin Compatible With LT1640L/LT1640H

Operates from –18V to –80V

Programmable Overvoltage Protection

Programmable Undervoltage Lockout

Power Good Control Output

Bell-Core Compatible ON/OFF Threshold

Central Office Switching

–48V Distributed Power Systems

Negative Power Supply Control

The LT

4250L/LT4250H are 8-pin, negative 48V Hot Swap™

controllers that allow 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 tran-

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

programmable undervoltage threshold or greater than

the overvoltage threshold. A programmable current limit

protects the system against shorts. After a 500μs timeout

the current limit activates the electronic circuit breaker.

The PWRGD (LT4250L) or PWRGD (LT4250H) signal can

be used to directly enable a power module. The LT4250L

is designed for modules with a low enable input and the

LT4250H for modules with a high enable input.

The LT4250L/LT4250H are available in 8-pin PDIP and

SO packages

LT4250L

SENSE

†

470nF

25V

†

15nF

100V

0.1μF

100V

100μF

100V

IRF530

10Ω

†

1k, 5%

†

549k

†

10k

†

0.02Ω

–48V RTN

(SHORT PIN)

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 =

38.5V

GATE DRAIN

PWRGD

4250 TA01a

OUT

SENSE

TRIM

SENSE

–

OUT

–

ON/OFF

LUCENT

JW050A1-E

100μF

16V

–48V

INPUT 1

–48V

INPUT 2

RELEASE

AT 43V

†

6.49k

0.1μF

10V

AND

DRAIN

20V/DIV

(Q1)

5A/DIV

500μs/DIV

4250 TA01b

Summary of content (14 pages)

PAGE 1
LT4250L/LT4250H Negative 48V Hot Swap Controller FEATURES DESCRIPTION n The LT®4250L/LT4250H are 8-pin, negative 48V Hot Swap™ controllers that allow 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.
PAGE 2
LT4250L/LT4250H ABSOLUTE MAXIMUM RATINGS (Note 1), All Voltages Referred to VEE Supply Voltage (VDD – VEE) ...................... –0.3V to 100V PWRGD, PWRGD Pins ............................. –0.3V to 100V SENSE, GATE Pins ..................................... –0.3V to 20V UV, OV Pins ................................................ –0.3V to 60V DRAIN Pin ................................................... –2V to 100V Maximum Junction Temperature...........................
PAGE 3
LT4250L/LT4250H ELECTRICAL CHARACTERISTICS The l 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 DC VDD Supply Voltage Operating Range IDD Supply Current VUVL Undervoltage Lockout l UV = 3V, OV = VEE, SENSE = VEE 18 l 1.6 80 V 5 mA 15.
PAGE 4
LT4250L/LT4250H TYPICAL PERFORMANCE CHARACTERISTICS Supply Current vs Supply Voltage Supply Current vs Temperature 1.8 VDD = 48V 1.5 1.4 1.3 1.2 13 GATE VOLTAGE (V) 1.6 1.4 1.3 1.2 11 10 9 8 7 20 0 40 80 60 SUPPLY VOLTAGE (V) 1.0 –50 100 –25 0 25 50 TEMPERATURE (°C) 75 6 100 0 15.0 55 48 54 47 13.0 12.5 GATE PULL-UP CURRENT (μA) TRIP VOLTAGE (mV) 14.5 53 52 51 50 49 12.
PAGE 5
LT4250L/LT4250H PIN FUNCTIONS PWRGD/PWRGD (Pin 1): Power Good Output Pin. This pin will latch a power good indication when VDRAIN is within VDL of VEE and VGATE is within VGH of ΔVGATE. This pin can be connected directly to the enable pin of a power module. When the DRAIN pin of the LT4250L is above VEE by more than VDL or VGATE is more than VGH from ΔVGATE, the PWRGD pin will be high impedance, allowing the pull-up current of the module’s enable pin to pull the pin high and turn the module off.
PAGE 6
LT4250L/LT4250H BLOCK DIAGRAM VDD – UV UVLO + VCC AND REFERENCE GENERATOR VCC REF OUTPUT DRIVE REF – OV + PWRGD/PWRGD LOGIC 50mV –+ – + 500μs DELAY GATE DRIVER + + – – VDL VEE + – +– VGH ΔVGATE 4250 BD VEE SENSE GATE DRAIN 4250lhfa 6
PAGE 7
LT4250L/LT4250H TEST CIRCUIT R 5k V+ 5V PWRGD/PWRGD OV VOV VDD + – DRAIN UV OV VDRAIN LT4250L/LT4250H + – DRAIN 20V 48V LT4250L/LT4250H 10k 10Ω GATE UV VUV VEE + – PWRGD/PWRGD VDD 48V 0.1μF VUV SENSE IRF530 GATE VEE SENSE VSENSE 10Ω 4250 F01a 4250 F01b Figure 1a. Test Circuit 1 Figure 1b. Test Circuit 2 TIMING DIAGRAM 2V 1.255V OV 2V 1.235V 1.125V UV 0V 1.255V 0V tPHLOV GATE tPLHOV 1V 1V tPHLUV GATE tPLHUV 1V 4250 F02 Figure 2.
PAGE 8
LT4250L/LT4250H APPLICATIONS INFORMATION where CL is the total load capacitance = C3 + C4 + module input capacitance. Hot Circuit Insertion 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 9
LT4250L/LT4250H APPLICATIONS INFORMATION DRAIN voltage has finished ramping, the GATE pin then ramps to its final value. Current Limit/Electronic Circuit Breaker The LT4250 features a current limit function that protects against short circuits or excessive supply currents. If the current limit is active for more than 500μs the electronic circuit breaker will trip.
PAGE 10
LT4250L/LT4250H APPLICATIONS INFORMATION A circuit that automatically resets the circuit breaker after a current fault is shown in Figure 10. 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
LT4250L/LT4250H APPLICATIONS INFORMATION Undervoltage and Overvoltage Detection The UV (Pin 3) and OV (Pin 2) pins can be used to detect undervoltage and overvoltage conditions at the power supply input. The UV and OV pins are internally connected to analog comparators with 130mV and 20mV of hysteresis respectively. When the UV pin falls below its threshold or the OV pin rises above its threshold, the GATE pin is immediately pulled low. The GATE pin will be held low until UV is high and OV is low.
PAGE 12
LT4250L/LT4250H APPLICATIONS INFORMATION ACTIVE LOW ENABLE MODULE –48V RTN (SHORT PIN) VIN+ VOUT+ –48V RTN 8 VDD LT4250L R4 3 UV 2 OV R6 – VGH + + – ΔVGATE + VDL VEE C3 7 GATE SENSE 5 6 C1 R2 R3 C2 4 R1 1 ON/OFF VIN– VOUT– DRAIN * 3 Q2 VEE – 4 –48V * DIODES INC. SMAT70A 1 + – R5 PWRGD + GATE 2 4250 F13 Q1 Figure 13. Active Low Enable Module –48V RTN (SHORT PIN) PWRGD –48V RTN R4 549k 1% R5 6.
PAGE 13
LT4250L/LT4250H PACKAGE DESCRIPTION N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .300 – .325 (7.620 – 8.255) .065 (1.651) TYP +.035 .325 –.015 ( .130 ± .005 (3.302 ± 0.127) .045 – .065 (1.143 – 1.651) .008 – .015 (0.203 – 0.381) +0.889 8.255 –0.381 .400* (10.160) MAX 7 6 5 1 2 3 4 .255 ± .015* (6.477 ± 0.381) .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 .100 (2.54) BSC ) 8 (0.457 ± 0.076) N8 1002 NOTE: 1.
PAGE 14
LT4250L/LT4250H TYPICAL APPLICATION application using the Lucent FLTR100V10 filter module is shown in Figure 15. When using a filter, an optoisolator is required to prevent common mode transients from destroying the PWRGD and ON/OFF pins. Using an EMI Filter Module Many applications place an EMI filter module in the powerpath to prevent switching noise of the module from being injected back onto the power supply. A typical –48V RTN (SHORT PIN) –48V RTN R7 51k 5% 8 VDD R4 549k 1% R5 6.