Rev. C 05/15

3

SEN012-013

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Applications Considerations

The maximum voltage that the device can sustain across the

VOLTAGE SUPPLY and GROUND pin is 16 V. The maximum voltage

that any of the source channels can be at with respect to the ground

terminal is 6.5 V. SENZero has a typical on state resistance of

approximately 500 W at room temperature. The device is therefore

typically used in series with high ohmic value resistors where this on

resistance is a small percentage of the total series impedance.

It is not necessary to provide a local bypass capacitor on the

VOLTAGE SUPPLY pin.

Operating Configurations for the SENZero

One configuration to power up the SENZero is shown in Figure 8. In

this circuit, SENZero is powered up from an unregulated bias winding

through a simple series pass regulator formed by Q1, R

B and VZ. This

configuration ensures the VCC voltage is limited even if the maximum

bias voltage exceeds 16 V. During power-down, as soon as the bias

voltage falls below V

Z, SENZero will turn off.

The series pass transistor Q1 is necessary only if the bias winding

voltage regulation is not tight enough (unregulated). If the voltage

on the bias winding is regulated or is such that the voltage on the

VOLTAGE SUPPLY pin can be maintained in the range 6 V < VCC < 16 V,

then the series pass transistor (Q1, R

B and VZ) can be eliminated.

Figure 8. SENZero Powered from an Unregulated Bias Winding Through a

Series Pass Regulator. Device is Enabled when Bias Voltage is

Present.

PI-6052-072010

Unregulated

Bias

Q1

(2N3904)

VZ

SENZero

VCC

G

D1

D2

S1

S2

RB

(2 k

Ω)

PI-6051-072010

ON/OFF

Disable

Regulated

Auxiliary

Q1

(2N3906)

RB

(2 k

Ω)

SENZero

VCC

G

RA

(20 k

Ω)

D1

D2

S1

S2

PI-6053-110510

Unregulated

Bias

Q1

(2N3904)

VZ

SENZero

VCC

G

D1

D2

S1

S2

RB

(2 k

Ω)

RB

(100 k

Ω)

ON/OFF

Enable

Q2

(2N3906)

A configuration that can be used to trigger remote-off functionality is

shown in Figure 9. In this configuration, a regulated auxiliary output

is used to power the IC. Transistor Q1 serves as the ON/OFF switch

which is commanded by the Enable/Disable signal at its base.

Figure 9. SENZero Powered from a Regulated Auxiliary Winding.

An alternative remote-off configuration is shown in Figure 10 where

an unregulated bias voltage supplies the SENZero through a series

pass regulator similar to the one shown in Figure 8. However the

circuit of Figure 10 includes an ON/OFF transistor Q2. In other

versions of this circuit Q2 can be replaced by an optocoupler allowing

the ON/OFF disable signal to be communicated from a secondary of

the power supply such as in PC power supplies.

Figure 10. A Modified Version of an Unregulated Bias Winding Supplying Power

Through a Series Pass Regulator. Transistor Q2 Provides Remote-Off

Functionality.