LTC7000 datasheet(13/28 Pages) LINER

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LTC7000/LTC7000-1

7000fa

For more information www.linear.com/LTC7000

applicaTions inForMaTion

to values between 20mV and 75mV. The value of resistor

for a particular sense threshold voltage can be selected

using Figure 2 or the following equation:

RISET =

Δ VTH

0.5µA

Where 20mV< ΔVTH < 75mV.

ISET RESISTOR TO GROUND (k)

90 120 150 180 210 240

7000 F02

Figure 2. RISET Selection

Optional filtering can be placed in series with the SNS– pin

as shown in Figure 3. Note that the SNS– pin takes 4µA

of bias current which will affect the current sense and

current monitoring functions. The value of RFLT needs to

be less than 250Ω to keep current sensing error less than

1mV due to the bias current associated with SNS– pin.

SNS+

SNS–

TGUP

TGDN

7000 F03

LTC7000/

LTC7000-1

INP = LO, 0µA

INP = HI, 4µA

RFLT

CFLT

RSNS

POWER

LOAD

Figure 3. Sense Pins Filtering

Fault Timer and Fault Flag

The LTC7000/LTC7000-1 includes an adjustable fault

timer. Connecting a capacitor from the TIMER pin to

ground sets the delay period before the external MOSFET

is turned off during an overcurrent fault condition. The

same capacitor also sets the cooldown period before the

external MOSFET is allowed to turn back on. Once a fault

condition is detected, a 100µA current charges the TIMER

pin. When the voltage on the TIMER pin reaches 1.3V, the

FAULT pin pulls low to indicate the detection of a fault

condition and provide warning of an impending power

loss. After the TIMER voltage crosses the 1.4V thresh-

old, TGDN is immediately pulled to TS turning off the

external MOSFET. The on-time of the external MOSFET,

TOVER_CURRENT, during an overcurrent event is given by

the following equation:

TOVER_CURRENT =

1.4V • CTIMER

100µA

+1.5µs

The warning time, TWARNING, generated by an overcurrent

event is given by the following equation:

TWARNING =

0.1V • CTIMER

100µA

+1.5µs

If the overcurrent fault condition disappears before

TIMER has reached 1.4V, TIMER is discharged by a

2.5µA current. If TIMER had reached 1.3V (FAULT has

gone low) and the overcurrent fault condition disappears,

TIMER is discharged with a 2.5µA current and FAULT will

be reset when TIMER reaches 0.4V. The on-time and

warning times are shown graphically in Figure 4.

TIME

VTMR (V)

7000 F04

TOVER_CURRENT

14ms/µF

TWARNING

1ms/µF

TFAULT

13ms/µF

1.4

1.3

Figure 4. Fault Timer Trip Points

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