SEN012-013
Applications Considerations
The maximum voltage that the device can sustain across the
VCC and G 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 approxi-
mately 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
VCC pin.
Operating Configurations for the SENZero
One configuration to power up the SENZero is shown in Figure 7.
In this circuit, SENZero is powered up from an unregulated bias
winding through a simple series pass regulator formed by Q1,
R
B
and V
Z
. 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 VCC pin can be maintained in the range 6 V <
VCC < 16 V, then the series pass transistor (Q1, R
B
and V
Z
) can
be eliminated.
Unregulated
Bias
Q1
(2N3904)
VCC
D1
D2
A configuration that can be used to trigger remote-off
functionality is shown in Figure 8. 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.
Regulated
Auxiliary
Q1
(2N3906)
VCC
D1
D2
R
A
(20 kΩ)
R
B
(2 kΩ)
SENZero
Disable
ON/OFF
G
S1
S2
PI-6051-072010
Figure 8.
SENZero Powered From a Regulated Auxiliary Winding.
An alternative remote-off configuration is shown in Figure 9
where an unregulated bias voltage supplies the SENZero
through a series pass regulator similar to the one shown in
Figure 7. However the circuit of Figure 9 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.
Unregulated
Bias
Q2
(2N3906)
R
B
(2 kΩ)
Q1
(2N3904)
VCC
D1
D2
R
B
(2 kΩ)
V
Z
G
S1
S2
SENZero
V
Z
G
S1
S2
PI-6053-110510
SENZero
ON/OFF
R
B
(100 kΩ)
Enable
PI-6052-072010
Figure 9.
Figure 7.
SENZero Powered from an Unregulated Bias Winding Through a Series
Pass Regulator. Device is Enabled When Bias Voltage is Present.
A Modified Version of an Unregulated Bias Winding Supplying Power
Through a Series Pass Regulator. Transistor Q2 Provides Remote-Off
Functionality.
3
www.powerint.com
Rev. B 11/05/10
POWERINT [ POWER INTEGRATIONS, INC. ]
