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LTC4216IDE-TRPBF

Ultralow Voltage Hot Swap Controller

Linear Technology 

LTC4216

Applications Information

Power-Up into an Output-Short

Figure 10 shows the timing diagram in the case when the

output is a dead short during power-up. As GATE ramps

up at time point 6, the MOSFET current increases due to

the output short causing the voltage drop across the sense

resistor to rise above 25mV. FILTER sources 60µA, charg-

ing the external capacitor. At time point 7, GATE regulates

to limit the output current to 40mV/RSENSE. If the output

continues to be in analog current limit when the FILTER

pin voltage reaches its threshold (1.253V) at time point

8, the circuit breaker trips and GATE is pulled low. The

device latches-off and FAULT is pulled low, indicating a

fault condition. The FILTER capacitor discharges through

a 2.4µA pull-down until the device resets.

Resetting the Electronic Circuit Breaker

When the LTC4216’s electronic circuit breaker is tripped

during a fault condition, FAULT is asserted low and the

RESET, SS and GATE pins are all pulled to ground. This is

shown in the timing diagram of Figure 11. The LTC4216

remains latched-off until the external fault is cleared. To

clear the internal fault latch and restart the device, pull

the ON pin low (< 0.4V) at time point 4 for at least 100µs,

after which the FAULT will go high at time point 5. Tog-

gling the ON pin from low to high (> 0.8V) initiates a new

start-up cycle.

Sense Resistor Considerations

The circuit breaker trip threshold of 25mV and the value

of the sense resistor, RSENSE, connected between the

SENSEP and SENSEN pins, determine the trip current level

as given by Equation (10). If the fault current level exceeds

the analog current limit, the current is limited to a value

given by Equation (11). Should the overload condition exist

for more than one fault filter delay as given by Equation

(2), the circuit breaker trips and the device is latched-off.

ITRIP(CB)

=

∆VCB(TH)

RSENSE

=

25mV

RSENSE

(10)

IACL

=

∆VACL(TH)

RSENSE

=

40mV

RSENSE

(11)

For a new circuit design, the sense resistor value is first

calculated from the maximum operating load current under

normal conditions and the minimum circuit breaker trip

threshold. This is given by:

RSENSE

=

∆VCB(TH,MIN)

ILOAD(MAX)

=

21.5mV

ILOAD(MAX)

(12)

CIRCUIT BREAKER TRIPS

AND LATCHED-OFF

MILD

OVERCURRENT

RESET PULLED LOW

DUE TO POWER BAD

FAULT LATCH

RESET

ON

SS

GATE

VOUT

SENSEP-SENSEN

TIMER

FILTER

FAULT

RESET

1

23 45 67

8

0.8V

10µA

1µA

10µA

TRACKS SS RAMP

VGATE – VOUT < VGS(TH)

GATE

REGULATING

FPD

VTMR(TH)

2µA

25mV

40mV

60µA

FAULT

FILTER

DELAY

VFILT(TH) 2.4µA

4216 F10

ON

SS

GATE

VOUT

SENSEP-SENSEN

FILTER

FAULT

RESET

1

23

45

0.4V

FPD

25mV

<40mV

VFILT(TH)

60µA

POWER BAD

VFB < 0.6V

2.4µA

tRST(ONLO)

4216 F11

Figure 10. Power-Up into an Output-Short and

Circuit Breaker Trips

Figure 11. Mild Overcurrent Circuit Breaker Trips Followed by

Device Reset

4216fa

For more information www.linear.com/LTC4216

17

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