LTC4213 datasheet(16/22 Pages) AD

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LTC4213

Rev. A

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Load Supply Power-Up Before VCC

Referring back to Figure 1, the VIN load supply can also

be powered up before VCC. Figure 5 shows the timing

diagram with the VIN load supply active initially. An inter-

nal circuit ensures that the GATE pin is held low. At time

point 1, VCC clears UVLO and at time point 2, ON clears

0.8V. 60µs later at time point 3, the GATE is ramped up

with 100µA. At time point 4, GATE reaches the external

MOSFET threshold VTH and VOUT starts to ramp up. At

time point 5, VSENSEN is near its peak. At time point 6, the

circuit breaker is armed and the circuit breaker can trip if

∆VSENSE > VCB. At time point 7, the GATE voltage peaks.

50µs after time point 6, READY goes HIGH.

Start-up Problems

There is no current limit monitoring during output

charging for the Figure 5 power-up sequence where the

load supply is powered up before VCC. This is because

the GATE voltage is below ∆VGSARM and the MOSFET

may not reach the specified RDS(ON). The VIN load sup-

ply should have sufficient capability to handle the inrush

as the output charges up. For proper startup, the final

APPLICATIONS INFORMATION

Figure 5. Load Supply Power-Up Before VCC

VON > 0.8V

Vth

VCC, VON

CIRCUIT BREAKER ARMS

READY SIGNALS

VREADY

VSENSEN

VSENSEP

RESET MODE

NORMAL CYCLE

tREADY

STARTUP CYCLE

tDEBOUNCE

VGATE

4213 F05

VSENSEP – VSENSEN = VCB

VGATE MAXES OUT

VCC > 2.07V

∆VGSARM + VSENSEN

∆VGSMAX + VSENSEN

LTC4213 Datasheet(PDF) 16 Page - Analog Devices

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