LT4254 Linear Technology Corporation, LT4254 Datasheet
LT4254
Available stocks
Related parts for LT4254
LT4254 Summary of contents
Page 1
... If the supply remains in current limit for more than a programmable time, the N-channel MOSFET shuts off, the PWRGD output goes low and the LT4254 either automatically restarts after a time-out delay or latches off until the UV pin is cycled low. The RETRY pin sets whether the part will automatically restart after an overcurrent fault will latch off until the UV pin is cycled low ...
Page 2
... RETRY ........................................................ – 0.3 to 15V TIMER ..................................................... – 0.3V to 4.3V Maximum Input Current (TIMER) ....................... 100µA Operating Temperature LT4254C ................................................. 0°C to 70°C LT4254I ............................................. – 40°C to 85°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T ...
Page 3
... SENSE Pin Regulation Voltage vs Temperature, FB > –50 – 100 125 TEMPERATURE (°C) 4254 G02 LT4254 MIN TYP MAX UNITS µA 0.1 10 µA –1 –0.1 µA ● – 60 – 120 –180 µA ● ...
Page 4
... LT4254 W U TYPICAL PERFOR A CE CHARACTERISTICS I vs Temperature CC 2 36V 24V CC 1 10.8V CC 1.6 1.4 1.2 1.0 –50 – 125 100 TEMPERATURE (°C) 4254 G04 FB Pin Hysteresis vs Temperature 480 460 440 420 400 380 360 340 320 300 –50 – 100 125 TEMPERATURE (° ...
Page 5
... V (V) CC 4254 G17 UV Hysteresis vs Temperature 500 450 400 350 300 250 200 –50 – 100 125 TEMPERATURE (°C) 4254 G20 LT4254 TIMER Pin Pull-Down Current 3 25°C A 3.2 3.0 2.8 2.6 2.4 2 / # UV Threshold Voltage (High-to- Low) vs Temperature 3 ...
Page 6
... V : Input Supply Voltage. The positive supply input CC ranges from 10.8V to 36V for normal operation. I typically 1.9mA. An internal circuit disables the LT4254 for inputs less than 9.8V (typ). GND: Device Ground. This pin must be tied to a ground plane for best performance. FB: Power Good Comparator Input. FB monitors the output voltage through an external resistive divider ...
Page 7
... If the RETRY pin is floating or connected to a voltage above its 1.2V threshold, the LT4254 automatically restarts after a current fault. Under an output short-circuit condition, the LT4254 cycles on and off with a 3% on-time duty cycle. RETRY: Current Fault Retry. RETRY commands the opera- tional mode of the current limit. If the RETRY pin is floating, the LT4254 automatically restarts after a current fault ...
Page 8
... LT4254 W BLOCK DIAGRA GEN REF GEN 4V 7 RETRY – INTERNAL + 9.8V + 0.65V – + – 4.65V 8 SENSE 15 + OPEN- CIRCUIT 3.5mV DETECT – – CURRENT 12mV ~ 50mV LIMIT + + FOLDBACK – UV – 4V LOGIC UV + TIMER LOW – ...
Page 9
... The transient currents can permanently damage the con- nector pins and glitch the system supply, causing other boards in the system to reset. The LT4254 is designed to turn on a board’s supply voltage in a controlled manner, allowing the board to be safely inserted or removed from a live backplane. The ...
Page 10
... When the FB pin voltage goes above the low-to-high V threshold, the PWRGD pin goes high. Short-Circuit Protection The LT4254 features a programmable foldback current limit with an electronic circuit breaker that protects against short circuits or excessive load currents. The current limit is set by placing a sense resistor (R5) between V SENSE ...
Page 11
... The duty cycle under short-circuit con- ditions is 3% which prevents Q1 from overheating. Latch Off Operation If the RETRY pin is grounded, the LT4254 will latch off after a current fault. After the part latches off, it may be LT4254 0 ...
Page 12
... F09 Open FET Detection The LT4254 can be used to detect the presence of an open FET. When the voltage across the sense resistor is less than 3.5mV, the open collector pull-down device is shut off allowing the OPEN pin to be externally pulled high. ...
Page 13
... Figure 12. Delay Circuit for OPEN FET Detection LT4254 stays in current limit long enough for the TIMER pin to fully charge up to its threshold, the LT4254 will either latch off (RETRY = into the current limit hiccup mode (RETRY = floating). In either case, an open FET condition will be falsely signalled ...
Page 14
... In some applications it may be possible for the V ring below ground (due to the parasitic trace inductance). Higher current applications, especially where the output load is physically far away from the LT4254 will be more susceptible to these transients. This is normal and the LT4254 has been designed to allow for some ringing below ground ...
Page 15
... BSC .015 ± .004 × 45° .0532 – .0688 (0.38 ± 0.10) (1.35 – 1.75) 0° – 8° TYP .008 – .012 (0.203 – 0.305) TYP INCHES (MILLIMETERS) LT4254 R5 R SENSE V OUT Q1 R4 PWRGD OPEN GND 4254 F15 .189 – .196* (4.801 – ...
Page 16
... IRF530 D1 CMPZ5241B 11V V SENSE 324k 10Ω UV GATE R7 R2 IN4148W 100Ω 40.2k LT4254 C1 10nF 40.2k OPEN RETRY TIMER PWRGD C2 GND UV = 20V 33nF OV = 40V PWRGD = 18V COMMENTS 9V to 80V Operation, Active Current Limit, Autoretry/Latchoff Floating Supply from –15V, Active Current Limiting, Fast Circuit Breaker Floating Supply from – ...