LTC4213 datasheet(17/22 Pages) AD

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LTC4213

Rev. A

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load at time point 6 should be within the circuit breaker

limits. Otherwise, the system fails to start and the circuit

breaker trips immediately after arming. In most applica-

tions additional external gate capacitance is not required

unless CLOAD is large and startup becomes problematic.

If an external gate capacitor is employed, its capacitance

value should not be excessive unless it is used with a

series resistor. This is because a big gate capacitor with-

out resistor slows down the GATE turn off during a fault.

An alternative method would be a stepped ISEL pin to allow

a higher current limit during startup.

In the event of output short circuit or a severe overload,

the load supply can collapse during GATE ramp up due

to load supply current limit. The chosen MOSFET must

withstand this possible brief short circuit condition before

time point 6 where the circuit breaker is allowed to trip.

Bench short circuit evaluation is a practical verification

of a reliable design. To have current limit while powering

a MOSFET into short circuit conditions, it is preferred

that the load supply sequences to turn on after the circuit

breaker is armed as described in an earlier section.

Power-Off Cycle

The system can be powered off by toggling the ON pin

low. When ON is brought below 0.76V for 5µs, the GATE

and READY pins are pulled low. The system resets when

ON is brought below 0.4V for 80µs.

MOSFET Selection

The LTC4213 is designed to be used with logic (5V) and

sub-logic (3V) MOSFETs for VCC potentials above 2.97V

with ∆VGSMAX exceeding 4.5V. For a VCC supply range

between 2.3V and 2.97V, sub-logic MOSFETs should be

used as the minimum ∆VGSMAX is less than 4.5V.

APPLICATIONS INFORMATION

The selected MOSFET VGS absolute maximum rating

should meet the LTC4213 maximum ∆VGSMAX of 8V.

Other MOSFET criteria such as VBDSS, IDMAX, and RDS(ON)

should be reviewed. Spikes and ringing above maximum

operating voltage should be considered when choosing

VBDSS. IDMAX should be greater than the current limit. The

maximum operating load current is determined by the

RDS(ON) value. See the Calculating Current Limit section

for details.

Supply Requirements

The LTC4213 can be powered from a single supply or

dual supply system. The load supply is connected to the

SENSEP pin and the drain of the external MOSFET. In the

single supply case, the VCC pin is connected to the load

supply, preferably with an RC filter. With dual supplies,

VCC is connected to an auxiliary bias supply VAUX where

VAUX voltage should be greater or equal to the load sup-

ply voltage. The load supply voltage must be capable of

sourcing more current than the circuit breaker limit. If

the load supply current limit is below the circuit breaker

trip current, the LTC4213 may not react when the output

overloads. Furthermore, output overloads may trigger

UVLO if the load supply has foldback current limit in a

single supply system.

VIN Transient and Overvoltage Protection

Input transient spikes are commonly observed whenever

the LTC4213 responds to overload. These spikes can be

large in amplitude, especially given that large decoupling

capacitors are absent in hot swap environments. These

short spikes can be clipped with a transient suppressor

of adequate voltage and power rating. In addition, the

LTC4213 can detect a prolonged overvoltage condition.

When SENSEP exceeds VCC + 0.7V for more than 65µs,

the LTC4213’s internal overvoltage protection circuit

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