LTC4367 datasheet(16/30 Pages) AD

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LTC7000A

Rev. 0

For more information www.analog.com

APPLICATIONS INFORMATION

Cooldown Period and Restart

As soon as TIMER reaches 1.4V, TGDN is pulled to TS in an

overcurrent fault condition and the TIMER pin starts dis-

charging with a 2.5µA current. When TIMER reaches 0.4V,

TIMER charges with a 2.5µA current. When TIMER reaches

1.4V, it starts discharging again with a 2.5µA current. This

pattern repeats 32 times to form a long cooldown timer

period (TCOOL_DOWN) before retry (Figure 5).

If INP is cycled low, TGDN will be pulled to TS and TIMER

will be pulled low with an internal 100kΩ resistor. If INP is

cycled low during the cooldown period, the timer counter

will be reset. If INP then goes high, TGUP will pulled to

BST and the fault timer will be reactivated with the TIMER

voltage starting from it’s current value.

At the end of the cooldown period (when TIMER drops

below 0.4V for the 32nd time), the LTC7000A/LTC7000A-1

retries, pulling TGUP to BST and turning on the external

MOSFET. The FAULT pin will then go to a high impedance

state. The total cooldown timer period is given by:

TCOOL_DOWN =

63 • 1.0V • CTIMER

2.5µA

The retry duty cycle in percent is to a first order indepen-

dent of CT and is defined by:

100 • TOVER_CURRENT

TOVER_CURRENT + TCOOL_DOWN

To defeat the automatic retry, place a 100kΩ resistor in

parallel with the TIMER capacitor. Note that the time to

turn off from an overcurrent fault will be increased by 7%

and the FAULT pin will remain low indicating a fault has

occurred. To get the LTC7000A/LTC7000A-1 to retry and

to clear the fault flag the INP signal needs to cycle low

then back high.

Typical turn-off times and cooldown periods for some

standard value timer capacitors are shown Table 1:

Table 1. Fault Time for Typical Capacitors

CTIMER

(nF)

TOVER_CURRENT

(µs)

TCOOL_DOWN

(s)

Retry Duty Cycle

<0.1

0.0005

~0.6

0.025

0.06

142

0.250

0.06

100

1402

2.500

0.06

COOLDOWN PERIOD (TCOOL_DOWN)

7000A F05

TIMER

∆VSNS

V(TG-TS)

(TGUP SHORTED TO TGDN)

FAULT

>30mV

<30mV

0.4V

1ST

2ND

31ST

32ND

INP

1.30V

1.40V

Figure 5. Auto Retry Cool-Down Timer Cycle

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