Application Note
March 2010
Design Guidelines for Power Module
Remote On/Off Circuits
Introduction
The remote on/off feature on the board-mounted
power modules (BMPMs) allows the user to switch
the module on and off electronically. This feature pro-
vides greater flexibility in the start-up sequencing and
provides fault control of the user’s power system. this
application note outlines the types of remote on/off
circuits, explains the parameters defining their opera-
tion, and provides helpful design tips targeted at
robust remote on/off control.
Types of Remote On/Off Control
BMP modules are available in positive logic and/or
negative logic versions for remote on/off. Table 1
shows a cross-reference for naming conventions of
codes with the different logic types.
Table 1. Remote On/Off Naming Conventions
* Optional remote on/off logic.
Note:NA—not available.
Isolated-Closure Remote On/Off
An isolated closure is a closure with both high- and
low-impedance states that sinks current, but does not
source current. For on/off control, the closure is
between the ON/OFF pin and VI(–), and can be pro-
vided by a device such as a mechanical switch, and
open-collector transistor, or an optoisolator. Figure 1
shows an example of an optoisolator connected to a
BMPM. Note the Von/off is defined as the voltage at
the ON/OFF pin with respect to the VI(–) pin. Ion/off is
the current flowing out of the ON/OFF pin.
8-668
Figure 1. Isolated-Closure Remote On/Off
There are two types of isolated-closure on/off control
circuits used in BMPMs. With negative logic, when
Von/off is pulled low by the external closure, the unit
operates. When Von/off is left isolated to float high, the
unit is off. With positive logic, when Von/off is left
isolated to float high, the unit operates, and when
Von/off is pulled low or shorted to VI(–), the unit is off.
Table 2 summarizes the logic levels and module
states.
Table 2. Isolated-Closure Logic Table
BMP Code
Family
Example
Name
Without
On/Off
Example
Name with
Negative
Logic
Example
Name with
Positive
Logic
MA/MH005 MA005A NA NA
MC/MW/
ME005
MC005A NA NA
MA/MH010 MA010A MA010A1 NA
MC/MW/
ME010
MC010A MW010A1 NA
JC/JW030 NA JC030A1* JC030A
CC/CW/DC/
DW025XX
NA CC025BK1* CC025BK
CC/CW/DC/
DW025XXX
NA CC025ABK1* CC025ABK
FC/FW050/
100/150
NA FC150A NA
FE200 NA FE200A NA
JC050/100 NA JC100A1 JC100A*
JW050/100-
150
NA JW150A1 JW150A*
FW300 NA FW300A1 NA
FC/FW 250 NA FW250A1 NA
Logic State Negative
Logic
Positive
Logic
Logic Low–
Switch Closed
Module on Module off
Logic High–
Switch Open
Module off Module on
VI(+)
VI(-)
ON/OFF POWER
MODULE
OPTOISOLATOR Ion/off
Von/off
+
-
22 LINEAGE POWER
Application Note
March 2010
Remote On/Off Circuits
Design Guidelines for Power Module
Types of Remote On/Off Control (continued)
Isolated-Closure Remote On/Off (continued)
Isolated-closure negative-logic on/off control has been established as a Tyco standard being implemented in all
new designs. this logic provides accurate control of the module during start-up since the module starts in a known
state. Table 3 summarizes the electrical specifications for the ON/OFF pin and the switch for isolated-closure nega-
tive-logic on/off.
Table 3. Isolated-Closure Negative-Logic Remote On/Off
Table 4. Isolated-closure Positive-Logic Remote On/Off
Table 5. Level-Controlled Remote On/Off
Parameter Symbol Min Max Unit
Remote On/Off; Negative Logic:
Logic Low—Module On
Logic High—Module Off
Module Specifications:
On/Off current—Logic Low (switch closed)
On/Off Voltage:
Logic Low (switch closed)
Logic High (switch open)
Open-collector Switch Specifications:
Leakage Current—Logic High (Von/off = 18 V)
Output Low Voltage During Logic Low (Ion/off = 1 mA)
Ion/off
Von/off
Von/off
Ion/off
Von/off
—
0
—
—
0
1.0
1.2
18
50
1.2
mA
V
V
µA
V
Parameter Symbol Min Max Unit
Remote On/Off; Negative Logic:
Logic Low—Module On
Logic High—Module Off
Module Specifications:
On/Off current—Logic Low (switch closed)
On/Off Voltage:
Logic Low (switch closed)
Logic High (switch open)
Open-collector Switch Specifications:
Leakage Current—Logic High (Von/off = 11 V)
Output Low Voltage During Logic Low (Ion/off = 500 µA)
Ion/off
Von/off
Von/off
Ion/off
Von/off
—
0
—
—
0
500
0.4
11
10
0.4
µA
V
V
µA
V
Parameter Symbol Min Max Unit
Remote On/Off; Level Controlled:
Unit Off:
Voltage Level High
Source Current
Unit On:
Voltage Level Low
Sink Current
Von/off
Ion/off
Von/off
–Ion/off
2
25
—
—
8
160
1.25
10
V
µA
V
µA
LINEAGE POWER 3
Application Note
March 2010 Remote On/Off Circuits
Design Guidelines for Power Module
Types of Remote On/Off Control (continued)
Isolated-Closure Remote On/Off (continued)
Isolated-closure positive-logic on/off is used in several
BMPM families including the 674, Fx020, SK025, and
ME025. Table 4 summarizes the electrical specifica-
tions for the ON/OFF pin and the switch for isolated clo-
sure positive-logic on/off.
In order to satisfy the requirements for the low-imped-
ance state, the closure must maintain a voltage less
than the maximum logic-low on/off voltage while sink-
ing the maximum logic-low on/off current. These speci-
fications, therefore, define the maximum saturation or
contact voltage of the switch and the current-sink
requirement. The logic-high on/off voltage defines the
maximum voltage to which the ON/OFF pin floats when
the isolated closure is in the high-impedance state. The
isolated closure must be rated to handle the logic-low
on/off current during its low-impedance state and with-
stand the logic-high on/off voltage during its high-
impedance state. The specified leakage current is the
maximum allowable Ion/off while the switch is in the high-
impedance state. The leakage current of the selected
switch must be less than this value over the required
application temperature range.
For example, consider the negative -logic specification
of Table 3. To activate the module, the user’s switch
must go to a low-impedance state and be capable of
sinking up to 1 mA while providing less than 1.2 V with
respect to VI(–). In particular, high-saturation voltage
switches such as Darlington output optoisolators need
to be checked carefully against this specification. To
turn the module off, the switch must go to a high-
impedance state and be able to withstand the 18 V on
the output of the ON/OFF pin. The leakage current
must be less than 50 µA while the switch is blocking a
Von/off of 18 V over the required temperature range.
For negative-logic applications that do not require
remote on/off, the ON/OFF pin can be shorted to VI(–).
For positive-logic applications not requiring remote
on/off, leave the ON/OFF pin open. control of the on/off
with positive logic may require particular care because
a falsely triggered switch can result in an undesired
shutdown of the BMPM. If noisy traces are routed near
the remote ON/OFF pin, it may be advisable to add fil-
tering with a small capacitor (≅100 pF) between the
ON/OFF pin and VI(–). the capacitor prevents high-
frequency noise from triggering the on/off circuit.
Level-Controlled Remote On/Off
Some power modules employ a voltage-level-controlled
remote on/off. Table 5 shows the specification for a
level-controlled remote on/off.
Von/off is defined as the voltage at the ON/OFF pin with
respect to the VI(–) pin. Ion/off is the current flowing into
the ON/OFF pin. For this type of module, the ON/OFF
pin is an input, since control is achieved by applying a
voltage and injecting a current.
Voltage level high is the voltage range that must be
maintained at the ON/OFF pin (Von/off) to turn the unit
off. The source current must be provided in order to pull
the ON/OFF pin high. From Table 5, between 2 V and
8 V must be provided at the ON/OFF pin to turn the
module off. The module draws between 25 µA and
160 µA. Exceeding 8 V may damage the module. The
minimum source current can be used as a guideline for
the maximum amount of noise current that can be toler-
ated before shutdown of the module.
Voltage level low is the voltage range that must be
maintained at the ON/OFF pin (Von/off) to turn the unit
on. Sink current is the amount of current that the supply
must be able to sink to maintain a logic low. The polar-
ity of this current is opposite the source current. Table 5
specifies a level control that maintains less than 1.25 V
while sinking 10 µA.
Figure 2 shows a TTL output control. In order to meet
the data sheet specification example in Table 5, the
TTL gate must be capable of sourcing 160 µA and sink-
ing 10 µA at an ouput-low voltage less than 1.25 V. The
logic voltage, Vcc, must not exceed 8 V. An open-col-
lector logic gate with a pull-up resistor could also be
used here. A Vcc of 5 V with a 10 kΩ pull-up would be
appropriate for the Table 5 specifications.
8-669
Figure 2. Level control Using TTL Output
V
I
(+)
V
I
(-)
ON/OFF POWER
MODULE
I
on/off
V
on/off
+
-
V
CC
(+)
SYSTEM
ON/OFF
CONTROL
TTL GATE
44 LINEAGE POWER
Application Note
March 2010
Remote On/Off Circuits
Design Guidelines for Power Module
Types of Remote On/Off Control (continued)
Level-Controlled Remote On/Off (continued)
An example of a line-voltage driven circuit is shown in
Figure 3. The Zener diode is sized to clamp Von/off
below the maximum level high voltage, while the
resistor limits the power dissipation in the Zener. If a
Darlington optoisolator is used, the saturation voltage
must be less than the maximum level low voltage
(1.25 V in Table 5) to turn on the module.
8-670
Figure 3. Level Control Using Line Voltage
Design Guidelines
Power modules equipped with remote on/off respond
very quickly when the appropriate signal is applied to
the ON/OFF pin. this available speed gives users the
most flexibility in their individual applications. However,
the lack of filtering that makes this performance possi-
ble requires that users take certain precautions in their
applications. The following design guidelines aid the
user in developing robust, noise-insensitive circuits with
which to control the remote on/off.
Preventing High Leakage Current
As stated earlier, a switch with a high-impedance state
is required for control of the remote on/off. When in the
high-impedance state, switch leakage currents greater
than 50 µA may be sufficient to trigger the on/off to the
logic-low state. If a transistor is used as the switch,
leakage currents of this magnitude can occur if the
device is operated in an open-base configuration (see
Figure 4).
8-671
Figure 4. High-Leakage Open-Base Transistor
(Not Recommended)
Here, the typically small collector cut-off current (LCBO)
is amplified by the current gain of the transistor,
resulting in substantial leakage currents. In addition,
maximum leakage currents for the open-base arrange-
ment at temperature extremes are generally not speci-
fied by device vendors, and can therefore be very
unpredictable for the user. Consequently, use of a
base-emitter resistor, as shown in Figure 5, is highly
recommended to reduce leakage current and provide a
more robust design.
8-672
Figure 5. Recommended Base-to-Emitter Resistor
Configuration
Filtering Capacitively Coupled Noise
Designers should be cautions of circuits susceptible to
high-frequency noise. Circuits using an open-base
transistor as the switch can again be extremely sensi-
tive. Noise coupling into the base of the transistor
through parasitic capacitance is amplified by the
transistor gain, possibly generating enough collector
current to switch the on/off circuit to the logic-low state,
as shown in Figure 6.
V
I
(+)
V
I
(-)
ON/OFF POWER
MODULE
I
on/off
V
on/off
+
-
6.2 V
VI(+)
VI(-)
ON/OFF POWER
MODULE
Ion/off
Von/off
+
-
RB
ICBO
SYSTEM
ON/OFF
CONTROL
VI(+)
VI(-)
ON/OFF POWER
MODULE
Ion/off
Von/off
+
-
RB
SYSTEM
ON/OFF
CONTROL
RBE
LINEAGE POWER 5
Application Note
March 2010 Remote On/Off Circuits
Design Guidelines for Power Module
Design Guidelines (continued)
Filtering Capacitively Coupled Noise
(continued)
8-673
Figure 6. Susceptible to High-Frequency Noise
(Not Recommended)
To minimize switch noise susceptibility, route the path
leading to the base as short as possible and away from
any potentially noisy paths. Routing the base path
close to VI(–) traces provides some beneficial capaci-
tance. More importantly, use a base-emitter capacitor
and/or resistor to filter coupled noise (see Figure 7).
Circuits in noisy environments may benefit from a
capacitor (≅100 pF) between the remote ON/OFF pin
and VI(–) for high-frequency decoupling.
8-674
Figure 7. Recommended Remote On/Off Layout
Minimizing Inductively Coupled Noise
Large loop areas are sensitive to inductively coupled
noise. Keep loops in circuits used to control the remote
on/off to a minimum area. For example, if a transistor is
used, minimize the loop area between the base and
emitter (use base-emitter resistors and/or capacitors
placed in close proximity to the transistor). Otherwise,
inductively coupled currents could be generated in the
transistor base, turning the device partially on. Place
the transistor close to the module to reduce the area of
the loop between the collector and emitter and the
power module pins (see Figure 8).
8-675
Figure 8. Minimize Loop Areas A and B
Using an Input Inductor
If an external inductor is used for input filtering, place
the switch that controls the module on/off on the mod-
ule side of the inductor. Otherwise, the inductor
appears in series with the switch, and the voltage
developed across the inductor can interfere with the
on/off control (see Figure 9). In addition, ensure that
the inductor does not appear in series with the base-
emitter resistor and/or the capacitor between the base
and emitter.
8-676
Figure 9. Properly Placing the Input Inductor.
V
I
(+)
V
I
(-)
ON/OFF POWER
MODULE
I
on/off
V
on/off
+
-
R
B
V
noise
ON/OFF
VI(-)
VI(+)
POWER
MODULE
V
I
(+)
V
I
(-)
ON/OFF
POWER
MODULE
R
BE
C
BE
B
A
VI(+)
VI(-)
ON/OFF
POWER
MODULE
RBECBE
VI
LI
Application Note
March 2010
Remote On/Off Circuits
Design Guidelines for Power Module
March 2010
AP97-038EPS (Replaces AP94-019EPS)
Design Guidelines (continued)
Start-Up Sequencing
Some start-up sequences can provide a sneak inrush-
current path through the remote on/off circuit of the
module. In general, the remote ON/OFF pin is normally
either open or tied to VI(–) (perhaps using a long finger
on a circuit card) for the start-up sequence. If the pin is
open, no sneak paths should be present. However,
suppose an isolated-closure positive-logic module is
being used (Type 2), and the remote ON/OFF pin is
tied to the VI(–) voltage to keep the module off while the
circuit card is inserted in the system. If the VI(+) voltage
is applied to the module before the VI(–) is applied, the
transistor internal to the BMPM’s remote on/off circuit
can become reverse biased with the input voltage.
Overvoltage stress will break down the transistor and
destroy the BMPM remote on/off circuit. In this case,
ensuring VI(–) is applied before VI(+) helps avoid any
problem.
Summary
Several types of fast, high-gain circuitry are used to
provide the on/off feature. Be sure to follow simple
noise-reduction techniques to prevent coupled noise
from begin amplified and disrupting desired operation.
The noise concerns discussed above are augmented
once a circuit pack is operating in a system environ-
ment where thermal and noise stresses are at their
worst.
Most of the discussion above focused on problems that
can result in the false turn-on of the user’s switch. In
modules with positive logic, this false trigger is usually
much more troublesome, since the switch turn-on
causes a power module shutdown. Negative logic,
where the switch is closed during normal operation,
eliminates many of the noise issues described here.
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