 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC1642A Datasheet(PDF) 9 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC1642A Datasheet(HTML) 9 Page - Linear Technology |
|
|
9 / 16 page  9 LTC1642A 1642af 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 LTC1642A limits the charging currents drawn by a board’s capacitors, allowing safe insertion into a live backplane. In the circuit shown in Figure 1 the LTC1642A and the external NMOS pass transistor Q1 work together to limit charging currents. Waveforms at board insertion are shown in Figure 2. When power is first applied to VCC the chip holds Q1’s gate at ground. After an adjustable delay a 25 µA current source begins to charge the external capacitor C2, so choose C2 to limit the inrush current IINRUSH charging the board’s bypass capacitance CLOAD according to the equation: C2 C • 25 A I LOAD INRUSH = µ An internal charge pump supplies the 25 µA gate current, ensuring sufficient gate drive to Q1. At 3V VCC the minimum gate drive is 4.5V; at 5V VCC the minimum is 10V; at 15V VCC the minimum is again 6.5V, due to an internal zener clamp from the GATE pin to ground. Resistor R3 limits this zener’s transient current during board insertion and removal and protects against high frequency oscillations in Q1. D1 provides additional protection against supply spikes. The delay before the GATE pin voltage begins ramping is determined by the system timer. It comprises an external capacitor C1 from the RST TMR pin to ground; an internal 2 µAcurrentsourcefeedingRSTTMRfromVCC;aninternal comparator, with the noninverting input tied to RST TMR and the inverting input tied to the 1.22V reference; and an internal NMOS pull-down. In standby, the NMOS holds RST TMR at ground. When the timer starts the NMOS turns off and the RST TMR voltage ramps up as the current source charges the capacitor. When RST TMR reaches 1.22V the timer comparator trips, the GATE voltage begins ramping up and RST TMR returns to ground. The timer delay is: tRSTTMR = (615ms/µF) C1. The second RST TMR cycle indicates that VOUT is within tolerance; it is discussed in the Undervoltage Monitor section. Figure 1. Supply Control Circuitry Powering-Up in Current Limit Ramping the GATE pin voltage limits the current to I = 25 µA • CLOAD/C2, where C2 is the external capacitor connected to the GATE and CLOAD is the load capacitance. If the value of CLOAD is uncertain, then a worst-case design can often result in needlessly long ramp times, and it may be better to limit the charging current by powering up in current limit. Current Limiting and Solid-State Circuit Breaker The current can be limited by connecting a sense resistor between the LTC1642A’s VCC and SENSE pins. When the voltage drop across this resistor reaches a limiting value, Figure 2. Timing at Board Insertion 100ms/DIV 1642a F02 OV 10V/DIV RST TMR 2V/DIV GATE 20V/DIV VOUT 20V/DIV GATE ON 14 SENSE 15 FAULT 6 4 BRK TMR 2 VCC 16 R2 0.010 Ω Q1 FDS6630A GND LTC1642A 8 RST TMR 3 1642a F01 R3 100 Ω R4 330 Ω D1 1N4705 18V C2 0.047 µF CLOAD + C1 0.33 µF C4 0.33 µF ALL RESISTORS ±5% UNLESS NOTED RESET DELAY = 200ms SHORT-CIRCUIT DURATION = 10ms VIN 12V 2.5A VOUT R7 24k R10 30k |
Similar Part No. - LTC1642A |
|
Similar Description - LTC1642A |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
