 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC1643AH Datasheet(PDF) 11 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC1643AH Datasheet(HTML) 11 Page - Linear Technology |
|
|
11 / 16 page  11 LTC1643AL LTC1643AL-1/LTC1643AH 1643afb APPLICATIONS INFORMATION Timer During a power-up sequence, a 22 µA current source is connected to the TIMER pin (Pin 4) and current limit faults are ignored until the voltage ramps to within 0.9V of 12VIN (Pin 1). This feature allows the chip to power up a PCI slot that can accept boards with widely varying capacitive loads on the supplies. The power-up time will be: t CV II ON SUPPLY SUPPLY LIMIT LOAD ≅ − 2 • For CSUPPLY = 2000µF, VSUPPLY = 5V, ILIMIT = 7A, ILOAD = 5A, the turn-on time will be ~10ms. The timer period should be set longer than the maximum supply turn-on time but short enough to not exceed the maximum safe operating area of the pass transistor during a short circuit. The timer period will be: t C V A TIMER TIMER = •. 11 1 22 µ For CTIMER = 0.1µF, the timer period will be ~ 50ms. The TIMER pin (Pin 4) is immediately pulled low when ON (Pin 5) goes low. Thermal Shutdown The internal switches for the 12V and –12V supplies are protected by an internal current limit and thermal shut- down circuit. When the temperature of chip reaches 150 °C, all switches will be latched off and the FAULT pin (Pin 6) will be pulled low. Short-Circuit Protection During a normal power-up sequence, if the TIMER (Pin 4) is done ramping and a supply is still in current limit, all of the pass transistors will be immediately turned off and the FAULT pin (Pin 6) will be pulled low as shown in Figure 4. If a short circuit occurs after the supplies are powered up, the shorted supply’s current will drop immediately to the limit value (Figure 5). If the supply remains in current limit for more than 14.6 µs, all of the supplies will be latched off. The 14.6 µs delay prevents quick current spikes—for example, from a fan turning on—from causing false trips of the circuit breaker. The chip will stay in the latched-off state until ON pin (Pin 5) is cycled low then high, or the 12VIN pin (Pin 1) power supply is cycled. To prevent excessive power dissipation in the pass tran- sistors and to prevent voltage spikes on the supplies during short-circuit conditions, the current limit on each supply is designed to be a function of the output voltage. As the output voltage drops, the current limit decreases. Unlike a traditional circuit breaker function where huge currents can flow before the breaker trips, the current foldback feature assures that the supply current will be kept at a safe level and prevent voltage glitches when powering up into a short. The current limit for the 5V and 3.3V supplies is set by placing a sense resistor between 5VIN (Pin 13) and 5VSENSE (Pin 12) and between 3VIN (Pin 9) and 3VSENSE (Pin 10). The current limit will be set by: ILIMIT = 53mV/RSENSE For a 0.005 Ω resistor, the current limit will be set at 10.6A and fold back to 1.5A when the output is shorted. For a 0.007 Ω resistor, the current limit will be set at 7.6A and fold back to 1.1A when the output is shorted. The current limit for the internal 12V switch is set at 850mA folding back to 250mA and the –12V switch at 450mA folding back to 160mA. In systems where it is possible to exceed the current limit for a short amount of time, it might be necessary to prevent the analog current loop from responding quickly so the output voltage does not droop. This can be accom- plished by adding an RC filter across the sense resistor as shown in Figure 6. R4 should be 20 Ω or less to prevent offset errors. A 0.1 µF capacitor gives a delay of about 1.5 µs and a 1µF capacitor gives a delay of about 15µs. CompactPCI Application The LTC1643AL is designed for hot swapping CompactPCI boards. The typical application is shown in Figure 7. The 3.3V, 5V, 12V and –12V inputs to the LTC1643AL come from the medium length power pins. The long 3.3V, 5V and V(I/O) pins power up the pull-up resistors, bus precharge |
Similar Part No. - LTC1643AH_15 |
|
Similar Description - LTC1643AH_15 |
|
|
|
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
