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NIS5101

SMART HotPlug IC/Inrush Limiter/Circuit Breaker

ON Semiconductor 

NIS5101

The theoretical equation for the UVLO turn−on voltage is:

RUVLO

(kW)

+

215 Vin * 2970

46.8 * Vin

Where Vin is the desired turn−on voltage, and RUVLO is

the programming resistance from the UVLO pin to the

Input + pin.

The UVLO trip point voltage calculated through the

theoretical formula may show small variations with respect

to Figure 3, therefore it is recommended to use the formulas

gotten from the UVLO characterization, which are shown

below:

RUVLO (kW) = e [(y+4.4706) / 6.4484]; for TJ = 25°C

RUVLO (kW) = e [(y+4.6185) / 6.8525]; for TJ = 120°C

RUVLO (kW) = e [(y+5.7642) / 6.7234]; for TJ = −40°C

where “y” is the desired UVLO value.

Drain

Vreg

Input +

280 k

OVLO

400 k

11 V

40 k

Input −

400 k

Figure 18. Overvoltage Lockout Circuit

To reduce nuisance tripping due to transients and noise

spikes, a capacitor may be added from the UVLO pin to the

Input – pin. This will create a low pass filter with a cutoff

frequency of f. The required capacitance on this pin is:

ƪ ǒ Ǔƫ C +

1

2p · f

150 k )

RUVLO · 200 k

RUVLO)200 k

Overvoltage Lockout: The overvoltage shutdown circuit

is an optional protection feature that can be disabled by

simply grounding the OVLO pin.

This circuit contains an internal Zener diode/resistor

combination in series with the gate of a FET. When the

input + to input − voltage reaches a level sufficient to apply

the required gate voltage to the FET, operation of the

SMART HotPlug will be inhibited. There is a hysteresis

circuit built in that will eliminate on/off bursts due to noise

on the input. The equivalent circuit is shown in Figure 18.

The equation for the OVLO trip point is:

ROVLO

(kW)

+

290 Vin

113.7

*

*

3200

Vin

Where ROVLO is the overvoltage programming resistor

from the OVLO pin to Input +, and Vin is the desired trip

point for the overvoltage shutdown to occur.

The OVLO trip point voltage calculated through the

theoretical formula may show small variations with respect

to Figures 4, 5 and 6, therefore it is recommended to use the

formulas gotten from the OVLO characterization, which

are shown below:

ROVLO (kW) = e [(y+69.6) / 24.82]; for TJ = 25°C

ROVLO (kW) = e [(y+60.56) / 23.27]; for TJ = 120°C

ROVLO (kW) = e [(y+66.47) / 23.52]; for TJ = −40°C

where “y” is the desired OVLO value.

Similar to the undervoltage lockout circuit, the noise

sensitivity of this circuit can be reduced by adding a

capacitor from the OVLO pin to Input −. The capacitor

required for the desired pole frequency is:

COVLO

+

(1

)

31.3 · 10−6 · ROVLO)

2pf · ROVLO

Temperature Limit: The temperature limit circuit senses

the temperature of the Power FET and removes the gate

drive if the maximum level is exceeded. There is a nominal

hysteresis of 40°C for this circuit. After a thermal

shutdown, the device will automatically restart when the

temperature drops to a safe level as determined by the

hysteresis.

Current Limit: The SMART HotPlug uses a SENSEFET

to measure the Drain Current. The behavior of the

SENSEFET in a short circuit condition varies from that in

an overload because there is sufficient voltage across the

drain to source terminals for the sense current to follow the

ratio of the sense cells to main FET cells. This is not the

case when the device is fully enhanced, since there are only

a few millivolts from drain to source. In this condition, the

sense voltage follows a different set of equations.

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