Linear Power
Amplifier
Module
User's Guide
Version 2.0
Table of Contents
Technical Specifications.........................................................................................7
Absolute Maximum Ratings.....................................................................7
Amplifier Specifications...........................................................................7
Amplifier Board Layout.........................................................................................9
Pinouts....................................................................................................................11
User Connection Header........................................................................11
Amplifier Mode Select............................................................................13
Power Supply Monitor Enable..............................................................14
Integrator Reset Enable.........................................................................15
Amplifier Configuration Block..............................................................15
Power Supply...........................................................................................23
Load Connection.....................................................................................25
GND Lug..................................................................................................26
Offset Adjustment...................................................................................26
Current Limit Adjustment.....................................................................27
Status Indicator LEDs............................................................................29
External Fault Indication.......................................................................30
Amplifier Enable Inputs.........................................................................30
Command Signal.....................................................................................31
Current Monitoring................................................................................32
Table of Contents
Voltage / Current Selection Header..........................................13
Voltage Mode Gain Setting .......................................................16
Current Mode Configuration ...................................................18
Offset Adjustment Procedure....................................................27
Current Limit Adjustment Procedure......................................29
Installation.............................................................................................................33
Mechanical Mounting.............................................................................33
Cooling Fans............................................................................................34
Determining the Required Airflow for Cooling...................................36
Electrical Connections............................................................................37
Selecting a Power Supply.......................................................................38
Connecting A Single Unit.......................................................................39
Determining the Dissipated Power............................................35
Operating Voltage.......................................................................38
Current Handling Capability....................................................39
Power Supply Type.....................................................................39
i
Table of Contents
Connecting Multiple Units.....................................................................41
Appendix A............................................................................................................45
Dimensions...............................................................................................45
ii
List of Figures
Table of Figures
Figure 1. Layout of the amplifier board and the various features................................9
Figure 2. amplifier mode selection jumper....................................................................13
Figure 3. Power supply monitor jumper location.........................................................14
Figure 4. Integrator reset jumper detail........................................................................15
Figure 5. Amplifier configuration block details............................................................16
Figure 6. Schematic representation of the amplifier....................................................17
Figure 7. Simulink diagram showing the user adjustable values................................23
Figure 8. Power connection details.................................................................................24
Figure 9. Load connection details...................................................................................25
Figure 10. GND connection.............................................................................................26
Figure 11. Offset adjustment..........................................................................................27
Figure 12. Current limit setting......................................................................................29
Figure 13. Amplifier status indicator LEDs..................................................................30
Figure 14. Mounting hole locations A (green) or B (blue)............................................33
Figure 15. Mounting locations for the small (twin) fans..............................................34
Figure 16. Mounting location of the large fan...............................................................35
Figure 17. Single amplifier connections.........................................................................41
Figure 18. Multiple amplifiers connected with a single power supply........................42
Figure 19. Multiple power supplies to drive multiple power amplifiers.....................43
iii
List of Tables
List of Tables
Table 1. User Connection Header signal names and pinout........................................12
Table 2. Details of the various configuration options...................................................17
Table 3. Recommend values for the forward gain in current mode...........................18
Table 4. Factory configuration of the integration components...................................18
Table 5. Power supply connection..................................................................................24
Table 6. Amplifier output terminals..............................................................................25
Table 7. Ground lug connection.....................................................................................26
Table 8. Typical current limit settings...........................................................................28
Table 9. Current limit output pinouts............................................................................29
Table 10. Amplifier enable truth table...........................................................................31
Table 11. Command signal pinouts................................................................................31
Table 12. Current output pins........................................................................................32
iv
Key Features
• Linear - Designed for low noise
operation
• High Output Current:
7A Continuous output
9A Peak output
• Wide Power Supply Range:
27 Volts to 60 Volts
• Wide Bandwidth:
>10kHz in current mode
>10kHz in voltage mode
• Dual Mode Operation:
Voltage Mode
Current Mode
• Fully Protected:
Thermal Shutdown
Adjustable Current Limit
Power Supply Monitor
• Active High and Active Low
amplifier enable inputs
• Offset Trim Adjustment
• Fault Indicator Output
• Startup / Shutdown Circuitry
disables the amplifier until power
supplies stabilize
Linear Power
Amplifier Module
LPAM-1
Applications
• Voice Coil Actuators
• X-Y Stages
• Robotics
• Magnetic Bearings
Description
The Quanser Power Amplifier is a linear power amplifier designed to drive loads in either voltage
mode or current mode.
In the current mode configuration, the amplifier is best suited for inductive loads such as dc-motors and
voice coil actuators. The unit displays low noise, wide bandwidth and an offset voltage adjustable to
zero.
Designed to run from a single supply, the amplifier's features include; accurate current sensing,
selectable fixed gain configurations, current limiting, and thermal protection.
Technical Specifications
Technical Specifications
Absolute Maximum Ratings
Parameter Value Units
Supply Voltage 60 V
Output Current
Continuous
Peak
7
9
A
A
Input (command) Voltage
supply voltage = 27 V
supply voltage = 48 V
+/- 10
+/- 20
V
V
Operating Temperature
(ambient temperature, natural convection cooling)
Power de-rating occurs beyond this temperature.
50 °C
Amplifier Specifications
Parameter min max typical Units
Power Supply Range 27 60 30 V
Input Voltage (Differential, max)
Supply voltage = 27 V
Supply voltage = 48 V
20
40
V
V
Input Impedance 1 MOhm
Output Impedance <0.2 Ohms
Bandwidth
Voltage Mode
Current Mode
>10
>10
kHz
kHz
Power Amplifier Module User's Guide 7
Amplifier Specifications
Parameter min max typical Units
Disable input signal
high TTL level, 5V
low TTL level, 0V
1
1
mA
mA
Amplifier Fault output
TTL compatible, with 200 ohm resistor inline
05 V
(current limited to 25 mA)
Current Sense output (buffered) 1 mA
Current Limit Output
V/A
reference voltage 0.5 V / A 0.5
Offset Adjust Adjusts output to zero for
zero command (input)
signal.
8 Power Amplifier Module User's Guide
Amplifier Board Layout
Amplifier Board Layout
This section of the manual describes the general layout of the board, and the location of key
features. Refer to this diagram when making connections and when locating functions on
the board.
Ground Lug
Power
Load Connection
Figure 1. Layout of the amplifier board and the various features.
User Connection
Header
Indicator LEDs
Fault / Status
Voltage / Current
Select
Integrator Reset
Enable
Power Supply Monitor
Enable
Amplifier Configuration
Block
Offset
Adjust
Current Limit
Adjust
Power Amplifier Module User's Guide 9
Pinouts
Pinouts
This section explains the various connections that can be made to the amplifier module.
Note that all connections should be securely made with the proper connectors. Improper
connections may result in poor performance, or may possibly damage the amplifier and
other connected equipment.
User Connection Header
The user connection header is where the user will make the connections to the amplifier.
The command signal and the feedback signal (current measurement) are present on this
header
Power Amplifier Module User's Guide 11
User Connection Header
Pin Number Signal Comments
1 +5V Available for signal conditioning circuitry, 10mA
max.
2 GND Ground connection.
3 -5V Available for signal conditioning circuitry, 10mA
max.
4 REF - Command signal negative or ground reference.
5 REF + Command signal positive or signal.
6 Current Limit
Output of current limit setting.
Monitor
7 GND Ground connection.
8 Not used Do not make connections to this terminal.
9 Current Monitor Current measurement output, 0.5V/A
10 GND Ground connection.
11 /ENABLE Amplifier Enable input. This line must be at 0V for
the amplifier to operate.
12 GND Ground connection
13 ENABLE Amplifier Enable input. This line must be at 5V for
the amplifier to operate.
14 +5V Available for signal conditioning circuitry, 10mA
max.
15 FAULT OUTPUT Fault indication for the amplifier, external LED
connection
16 GND Ground connection
Table 1. User Connection Header signal names and pinout.
12 Power Amplifier Module User's Guide
Amplifier Mode Select
Amplifier Mode Select
Voltage / Current Selection Header
The amplifier is designed to function either as a voltage amplifier or a current amplifier.
Selection of what mode the amplifier operates in is by way of a jumper. Placing jumper J1
in the 1-2 position selects voltage mode. Placing the jumper in the 2-3 position selects
current mode. The default configuration for the amplifier is current mode, with the
jumper in the 2-3 position.
Voltage / Current
Select Jumper
Figure 2. amplifier mode selection jumper.
Voltage Mode
In this configuration, the amplifier accepts a command signal and outputs a voltage
proportional to the command signal. The signal can be amplified by the configurable gain
setting of the amplifier. See the section titled, “Amplifier Configuration Block” for details
on this procedure. Power is provided to the load at increased current driving capability, up
to a maximum of 7A continuous output.
In voltage mode, the commanded signal will correspond to an output voltage related by the
gain setting of the amplifier. For example, with a gain setting of 1, a 1 volt input signal will
produce a 1 volt output signal at the output terminals of the amplifier. Similarly, with a gain
setting of 4, a 1 volt command would provide 4 volts at the output of the amplifier. The
units of the gain are therefore expressed in terms of volts per volt (V/V).
The amplifier will be able to provide an output voltage approaching the supply voltage of
the amplifier. See the Technical Specifications section for details.
Current Mode
In the current mode configuration, the amplifier outputs the commanded current to the load.
Despite changes in the load, the amplifier will output the commanded current. The
Power Amplifier Module User's Guide 13
Amplifier Mode Select
amplifier uses a built in current feedback loop to continuously change the voltage applied to
the load so the commanded current is always applied to the load. The maximum continuous
current available is 7A. Consult the section titled, “Amplifier Configuration Block” for
details on matching the amplifier to your load.
In current mode, the input signal corresponds to a commanded current. Therefore the
output current of the amplifier is related to the input voltage by the current gain of the
amplifier implemented using external components. For example, with a current gain setting
of 1, a 1 volt input signal will produce a 1 amp output signal at the output terminals of the
amplifier. Similarly, with a gain setting of 4, a 1 volt command would provide 4 amps at the
output of the amplifier. The units of the gain are therefore expressed in terms of amps per
volt (A/V). The factory configuration is 2 Amps / Volt.
It is important to consider that the voltage at the output terminals is automatically adjusted
by the amplifier to provided the commanded current. For this reason, care must be taken to
ensure that the amplifier is being asked to do something that it can accomplish based on the
available power supply. The maximum current that the amplifier can provide is limited by
the supply voltage and the impedance of the load.
Power Supply Monitor Enable
The power amplifier employs a voltage monitoring system to ensure that safe startup and
shutdown conditions for the amplifier are met. This feature limits surge currents that may
be sent to the load at startup or shutdown. A delay of approximately 0.5 seconds is used
during turn on of the amplifier, and the amplifier will not be enabled until the power supply
has reached the minimum voltages. At voltages under the specified 27 volts minimum
operating voltage, the amplifier will not be enabled with this jumper in the 1-2 position. To
disable this feature install the jumper in the 2-3 position. The factory configuration is
with the power supply monitor enabled, with the jumper in the 1-2 position.
Power Supply
Monitor Jumper
Figure 3. Power supply monitor jumper location.
14 Power Amplifier Module User's Guide
Integrator Reset Enable
Integrator Reset Enable
Along with the power supply monitoring feature of this amplifier, an integrator reset feature
is provided. Jumper SW EN enables / disables resetting of the integrator of the amplifier.
With this jumper in the 1-2 position, the integrator used for the current feedback loop is
cleared or reset to zero when the amplifier is first powered up, or when the amplifier is
disabled. In the 2-3 position, this feature is disabled. The factory default configuration is
with the jumper in the 1-2 position, enabling the integrator reset feature.
Integrator Reset
Enable Jumper
Figure 4. Integrator reset jumper detail.
Amplifier Configuration Block
The amplifier configuration block allows customization of the amplifier to the user's needs.
These customizable features include:
• gain setting
• amplifier tuning
These features allow the user to customize the amplifier to suit a specific application.
Table 2 provides a description of the components used in the configuration block and the
functions that they serve. Figure 6 shows the schematic details of how the components
operate in the configuration of the amplifier.
Power Amplifier Module User's Guide 15
Amplifier Configuration Block
F
A B C D E F G H
Figure 5. Amplifier configuration block details.
Voltage Mode Gain Setting
In voltage mode, the total gain of the amplifier is determined by the components A, C, and
D in the configuration block. From the description in Table 2 and the schematic diagram in
Figure 6, the total gain can be calculated as the product of G1G2GF, where GFis the final
gain stage of the amplifier and is fixed to a value of 20.
GT=
G1×
G2×
G
It is important to note that when choosing resistor values to set the gains G1 and G2, that
the values chosen do not cause the amplifier to saturate. This means that the gains used
must keep the voltages below 11 volts.
16 Power Amplifier Module User's Guide
Amplifier Configuration Block
Row Part Name Function Default Value
A R36 This resistor with D sets the first gain stage of the
amplifier. The resulting gain is G1 = D/A.
B R33 Current loop feedback gain resistor. 1k
C R22 Sets the gain in voltage mode for the amplifier. The
resulting gain for this stage is G2 = C/1k.
D R55 With A, this resistor value sets the first gain stage
for the amplifier. The resulting gain for this stage is
G1 = D/A.
E C10 Current loop error feedback integration capacitor 22nF
F C9 Current loop feedback compensation capacitor –
typically use factory value of 2.2nF.
G - Do not make connections in this position. open
H - This enables the integrator clearing circuitry and
must be installed for it to function properly.
Table 2. Details of the various configuration options.
C
1k
J1
SW1
F
1k
Voltage
H
Current
EB
Gain = 20
Ref+
Ref-
Differential
Input
D
A
10k
10k
10k
2.2nF
short
Differential
Output
Current Monitor
/Enable
Enable
Figure 6. Schematic representation of the amplifier.
1k
500mV / A
Power
Monitor
J2
Shutdown
and
Enable Logic
Output Disable
SW1 - Integrator Reset
Power Amplifier Module User's Guide 17
Current Mode Configuration
In order to set the gain of the amplifier, you need to select components D and A. These set
the forward gain such that the amplifier delivers G Amps/V.
The equation for the forward gain of the amplifier is
D
G=2
A
Table 3 shows recommended values
G – Amps / V D – Ohms A - Ohms D / A
1 5000 10000 0.5
2 10000 10000 1
4 20000 10000 2
Table 3. Recommend values for the forward gain in current mode.
The bolded text shows the factory configuration.
Tuning the Amplifier
In current mode the amplifier must be tuned to the load inductance and resistance. This is
important to optimize its performance for the load.
The tuning components as configured at the factory are:
Component Purpose Value Units
E Integration gain capacitor 2.20E-008 Farads
B Loop gain resistor 1000 Ohms
Table 4. Factory configuration of the integration components.
By changing the above components you can adjust the current loop proportional and
integral gains.
18 Power Amplifier Module User's Guide
Do You Want an Integrator?
First you need to determine whether you want integration or not. The capacitor E will
introduce an integrator in the feedback loop in order to assure zero steady state error in
current independent of load resistance and back EMF. The disadvantage of using an
integrator in the current loop is the following: if you are using an actuator driving a load
with very little friction, the slightest offset in the input may cause a runaway in the motor
unless you are operating a stable closed loop externally. It is recommended that you first try
with an integrator and adjust the offset to zero. If the motor runs away in open loop with the
expected load, then you may want to completely eliminate the integrator by shorting
component E.
The drawback of removing the integrator is that the forward gain will now be load
dependent. The expected forward gain, with an integrator is:
D
G=2
A
With no integration however, the gain in the system now becomes:
G
=
D
2
A
10
Kp
R
10
load
Kp
where Kp is determined by the equation:
Kp=
B
1000
where B is the value of component B in ohms.
With Kp = 1 (B = 1 KOhm) , the gain will decrease as the load resistance increases as in
the following table:
Power Amplifier Module User's Guide 19
Kp = 1 ( B = 1 K)
R Load Gain
2 0.8333
4 0.7143
6 0.6250
8 0.5556
10 0.5000
Note that the gain depends on the load resistance and will not be consistent throughout the
operating temperature range of the load since the load resistance increases as the load
resistance gets warm. That is another reason for using the integration in the loop.
You may chose to increase the proportional loop gain Kp instead since the gain reaches
unity as Kp gets larger. For example setting Kp = 10 using a 10K resistor for B will result
in the following
Kp = 10 ( B = 10 K)
R Load Gain
2 0.9804
4 0.9615
6 0.9434
8 0.9259
10 0.9091
which shows that the gain is closer to unity even with load resistance changes. This gain
however may result in undesired ringing if the load inductance is too low.
Implementing an Integrator
The system is shipped with the integrator in the loop active. The system is tuned for the
following load:
20 Power Amplifier Module User's Guide
Parameter Value Units
R Load 4 Ohms
L Load 0.0001 Henry
with the following components for the compensation network:
Component Purpose Value Units
E Integration gain capacitor 2.20E-008 Farads
B Loop gain resistor 1000 Ohms
You can tune these values to optimize performance. A MATLAB and a Simulink model are
available that will simulate the system where you can adjust these parameters online. In
order to tune the amplifier for optimal performance perform the following; you will need a
signal generator and an oscilloscope.
Connect the signal generator to the input of the amplifier. Connect the load to the amplifier.
Connect the oscilloscope probe to the current sensor measurement. Apply a small amplitude
1KHz. square wave (about 100 mV p-p) - make sure the commanded amplitude does not
saturate the amplifier or blow the load!
Start with no integration – i.e. short components E or replace it with a large capacitor e.g. 2
microfarad.
Observe the step response of the system and tune as follows:
• If the response is too slow increase the loop gain by increasing resistance B.
• If there is too much high frequency ringing, reduce the loop gain by reducing B.
• Once B gives a satisfactory response, you will note that the steady state error is not zero.
• Start introducing integral gain by reducing the value of component E.
• If the steady state error does not diminish quickly increase the integral gain by reducing
the capacitance of E.
Power Amplifier Module User's Guide 21
• If there is too much overshoot due to integration reduce the integral gain by increasing
the capacitance of E.
• You may need to increase the loop gain using B to dampen the response after selecting
E.
Also note that the higher the inductance the more proportional loop gain you will require
and the less integral loop gain you will require. So for high inductance increase B & E.
Furthermore, note that the current rate of change is limited by the supply voltage and the
load inductance by the equation
dI
dt
=
Vs
L
Ampere
/
second
and will limit the practical bandwidth of the system.
Preliminary tuning may be performed using the MATLAB script or the Simulink simulation
supplied with the system as described below.
Using the MATLAB Script
You need to have MATLAB for this. Simply run the file current_amp_design.m from
MATLAB. This will display a step response and a frequency response and print the
theoretical - small signal - bandwidth of the system. The system is tuned for
Rload = 4 Ohm
Lload = 0.1mHenry
If you need to tune the system for a different load, open the file with a MATLAB Editor and
change the following lines to suit your load:
% Power supply voltage
Vmax = 28;
% Load parameters - Minimum inductance 0.1 mHenry
22 Power Amplifier Module User's Guide
Lload = .1e-3;
Rload = 4;
% tune these in the Simulink diagram or here
Comp_E = 22e-9; %integration capacitor - increase to reduce
integral gain standard 0.05 micro
Comp_B = 1e3; %feedback gain resistor - variable - increase to
increase loop gain
Then run the file again to see if the response as you would like it. Follow the tuning
procedure described above.
Using the Simulink Model
A Simulink model is also available. Open the model current_amp_i_c.mdl. Run the
MATLAB script current_amp_params.m. Run the simulation and open the two scopes to
observe the current step response. Tune the Load resistance and inductance to your
desired response.
Figure 7. Simulink diagram showing the user adjustable values.
Note that the Simulink model takes into account the non-linearity introduced by amplifier
voltage limits as well as other dynamic components in the amplifier that are not modeled in
Power Amplifier Module User's Guide 23
the small signal MATLAB model. This simulation is more realistic than the MATLAB
model.
For slow systems ( system with large inductance, > .01 Henry) you will need to slow the
signal generator frequency in order to observe the steady state response of the system. Note
that both these simulations give you a starting point for the tuning values and you may still
need to adjust these on the actual system.
Power Supply
Power must be applied to these pins with the correct polarity, otherwise the amplifier may
be damaged.
Only isolated-secondary type power supplies should be used. The power
supply should be a floating type supply, and not referenced to ground on
the secondary.
The amplifier employs an under-voltage lockout system to disable the amplifier in the event
that the supply voltage falls below 27 volts. This feature may be disabled by removing the
jumper J2 (RESET EN) from the 1-2 position and placing it in the 2-3 position. Note that
this action will disable the power-up / power-down circuitry as well, and may result in
surges at the output terminals of the amplifier. Power supply voltages below 27 volts may
affect the performance of the amplifier.
Reversing the power supply connection may result in permanent damage
to the amplifier.
Pin Number Function
1 POWER +
(27 – 60 Volts)
2POWER -
Table 5. Power supply connection.
24 Power Amplifier Module User's Guide
Pin 1
Pin Signal
1 Positive (+)
2 Negative (-)
Figure 8. Power connection details.
Load Connection
The load is connected to the amplifier at this connector. Note that the each of the pins is
duplicated within this connector for additional current handling capability. User
connections should make use of all the pins for optimal current handling ability.
The output of the amplifier is floating. It is not referenced to ground.
Pin Number Function
1 Motor-
2 Motor-
3 Motor+
4 Motor+
Table 6. Amplifier output terminals.
Power Amplifier Module User's Guide 25
Load Connection
GND Lug
Pin 1
Pin Signal
1 Load (-)
2 Load (-)
3 Load (+)
4 Load (+)
Figure 9. Load connection details.
The GND lug is provided for convenience where several amplifiers are connected together
(multiple channel application) and a common ground reference is needed. This is the only
ground that should be treated as common between the input/output signals and the amplifier
itself.
Do not use the negative (GND) power input to the amplifier as a ground
reference, or damage to the amplifier and/or your equipment may result.
Pin Number Function
1 Virtual Ground
Reference
(GND)
Table 7. Ground lug connection.
26 Power Amplifier Module User's Guide
Offset Adjustment
Figure 10. GND connection.
Offset Adjustment
A potentiometer is provided to allow setting the output voltage / current of the amplifier to
zero for zero commanded input. Turning the potentiometer to the right (clockwise)
increases the offset, making the value more positive.
Offset
Adjust
Figure 11. Offset
adjustment.
Offset Adjustment Procedure
The setting of the offset to zero requires a few special tools.
• Multimeter
• Small screwdriver
To set the offset of the amplifier to zero, follow the procedure shown below:
1. Command a zero input to the amplifier or short the command input pins together
(remove the input connections to prevent damaging the signal source).
2. Connect a multimeter to the output terminals of the amplifier.
3. Adjust the potentiometer until the meter reading displays zero (0.0V)
4. The output of the amplifier should now provide zero voltage / current when the
command is zero. Be sure to remove the short across the input pins of the amplifier if
Power Amplifier Module User's Guide 27
Offset Adjustment
one was placed there.
Current Limit Adjustment
Current limiting allows the user to set a maximum (peak) current that the amplifier will
provide to the load. The amplifier will provide current up the set current limit. Continuous
currents of 7 Amps are possible, while peak currents may reach 9 Amps. The current limit
is adjusted by means of a multi-turn potentiometer . The current limit setting is determined
by measuring the voltage present at the current limit output pin. The relationship for the
current limit setting and the current limit output is shown below.
Current LimitSetting=2×Current LimitOutput Voltage
Equation 1. Current limit output voltage to current limit setting relationship.
Current limit adjustment is provided by means of a multi-turn potentiometer. Turning the
potentiometer clockwise increases the current limit setting, while turning it counterclockwise will decrease the current limit setting. The voltage at the Current Limit Output
(pins 6 and 7 on the User Connection Header) should be measured for accurate
determination of the maximum current setting. A meter can be connected to these two pins
to measure the current limit setting. The output signal varies between 0 and 5 volts. A
setting of 3.5 volts gives a current limit setting of 7 amps, the maximum rated output for the
amplifier. Instantaneous currents, or peak currents may go as high as 9 A, with the output
set to 5 volts. The factory setting allows for maximum current to be delivered to the
load.
28 Power Amplifier Module User's Guide
Current Limit Adjustment
Current Limit
Measured Current
(Amps)
1 0.50
2 1.00
3 1.50
4 2.00
5 2.50
6 3.00
7 3.50
MAX 5.00
Table 8. Typical current limit settings
Limit Output
(Volts)
Current Limit
Adjust
Figure 12. Current limit setting.
Pin Number Function
6 Signal (0-5V)
7 GND
Table 9. Current limit output pinouts.
Power Amplifier Module User's Guide 29
Current Limit Adjustment Procedure
Adjustment of the current limit requires a few special tools:
• Multimeter
• Small Screwdriver
To adjust the current limit, follow this procedure:
1. Connect the multimeter to the terminals shown in (connector J1).
2. Adjust the trimpot to the desired voltage for the required current setting shown in Table
8, or follow the relationship of Equation 1.
Status Indicator LEDs
Status indication provides a visual means of determining the operating state of the
amplifier. The amplifier is provided with a thermal shutdown feature to prevent damage to
the amplifier. Indication of the status is provided by means of two LEDs and a secondary
output, the Fault Indicator output on pins 15 and 16 of the User Connection Header. The
indicator LEDs are green and red.
Green – Power good, amplifier ready.
Thermal shutdown
Amplifier disabled
Power supply fault
Flashing – entering thermal shutdown
Figure 13. Amplifier status indicator LEDs.
The flashing condition of the red LED indicates that the amplifier is entering thermal
shutdown. This situation typically occurs when the amplifier is driving large loads, or the
amplifier is inadequately cooled. The amplifier will continue to operate, but the output will
be temporarily shutdown during this interval.
External Fault Indication
The state of the red LED is duplicated on the fault output of the User Connection Header,
on pins 15 (signal) and 16 (GND). The output is current limited with a 200 ohm resistor,
30 Power Amplifier Module User's Guide
External Fault Indication
making the signal suitable for directly driving and external LED. Alternatively, the signal
may be buffered and used as a status indicator for the connection to external control
circuitry.
Amplifier Enable Inputs
The amplifier is provided with two inputs which must receive the proper signals before the
amplifier will become enabled. In the disabled state, the output of the amplifier goes into a
high impedance state. The inputs, /ENABLE and ENABLE are ANDed together to
determine the logical state. Table below shows the truth table for these connections.
ENABLE /ENABLE Amplifier Status
0V 0V Disabled
0V 5V Disabled
5V 5V Disabled
5V 0V ENABLED
Table 10. Amplifier enable truth table.
The /ENABLE input is tied to +5V through a 4.99k ohm resistor. The ENABLE input is
tied to GND (0V) through a 1k ohm resistor. This default configuration leaves the amplifier
in a normally disabled state.
Both the ENABLE and the /ENABLE inputs have specific thresholds that must met in order
for the amplifier to be enabled for operation.
Signal Threshold Minimum Maximum
ENABLE > 2.4V 0V 5V
/ENABLE < 0.8V 0V 5V
Power Amplifier Module User's Guide 31
Command Signal
Command Signal
The input signal to the amplifier is a differential type input. This signal is called the
reference signal, and is applied to the amplifier on the User Connection Header.
Connections should be made at pins 4, Ref- and pin 5, Ref+. The amplifier measures the
difference between the two signals present at this input and uses it as the command signal.
Therefore, when only a command input is connected, the amplifier will not be grounded.
A proper ground line should be connected to the ground lug of the amplifier if the system
design mandates a grounded connection.
Pin Number Function
4 Reference -
5 Reference +
Table 11. Command signal pinouts.
Current Monitoring
Outputs are provided for monitoring of the current delivered to the load by the amplifier.
These outputs are available whether the amplifier is used in current mode or voltage mode.
Pin Number Function
9 Current output
10 GND
Table 12. Current output pins.
The signal is calibrated to provide 0.5V / A. Therefore, for a 2 A current being delived to
the load, a 1 volt signal will be present between pins 9 and 10.
32 Power Amplifier Module User's Guide
Installation
Installation
Installation, mounting and information on making electrical connections to the amplifier
can be found in this section.
Mechanical Mounting
The amplifier is fitted with a series of mounting holes along two surfaces. These holes
make it possible to mount the amplifier to a surface in two different configurations.
Appendix A shows details of the heatsink of the amplifier. The user can use this drawing as
a reference when constructing enclosures or fixtures for the amplifier.
Proper mounting of the amplifier will also help cooling and prolong the service life of the
amplifier. A cooler amplifier runs better, and will perform better over the long term. The
surface that the amplifier is mounted to can aid in the cooling of the amplifier.
Care should be taken to ensure that the amplifier is not exposed to excessive moisture or
used in areas were metal debris may come into contact with the amplifier. In these
situations, a proper enclosure must be used to prevent the amplifier from being damaged,
and to reduce the risk of electrical shock.
Mounting Options
Figure 14. Mounting hole locations A (green) or B (blue).
Power Amplifier Module User's Guide 33
Cooling Fans
Cooling Fans
Most applications of the power amplifier module will require the use of cooling fans, to
maintain the amplifier at a safe operating temperature.
The heatsink of the amplifier has holes tapped to accept #8 mounting hardware. Either two
1.25” fans may be used, or one 2” fan can be used.
Additional mounting holes
Spacer
Figure 15. Mounting locations for the small (twin) fans.
Mounting of two smaller fans may be useful in situations where space is limited or where
the noise from a larger fan may be an issue. As well, dual fans does provide a degree of
redundancy in demanding applications.
Note that spacers are used to separate the fan from the surface of the heatsink to provide a
proper path for cooling. As well, attention should be paid to the direction of airflow.
Airflow should be flowing towards the surface of the heatsink. Determination of the proper
CFM rating for the selected fan depends highly on the application and the enclosure of the
amplifier. Note that the mounting surface of the amplifier may contribute to the total
effective cooling area. This may greatly reduce the airflow requirements of a fan. The
maximum power capacity of the amplifier is under 500W, so the maximum power that
would need to be dissipated cannot reach this value. As a result, a fan with a maximum
CFM rating of 30 CFM is required for applications where a 30°C temperature rise can be
tolerated. Keep in mind that the maximum operating temperature (ambient temperature) is
50°C.
34 Power Amplifier Module User's Guide
Cooling Fans
y
y
Spacer
Figure 16. Mounting location of the large fan.
Two fans rated for 4.5 CFM or 1 rated 9 CFM or greater should suffice for most
applications.
Determining the Dissipated Power
Calculation of the power dissipated by the amplifier is critical to determining the amount of
cooling required of the amplifier. Assuming the worst-case scenario of a DC output, the
power dissipated is given by any of the following:
PD=2×
PD=2×
PD=2×
The second and third equations are obtained by substituting Ohm's law for the required
parameter. Power dissipated P
heat in the amplifier, and must be removed by natural convection or through forced air
cooling.
I
V
R
I
load
output
load
load
×
×
V
×
V
suppl
V
suppl
−
supply
−
V
−
I
output
V
load
output
×
R
load
is given in Watts. This power will be given off as excess
D
Power Amplifier Module User's Guide 35
Determining the Required Airflow for Cooling
y
Determining the Required Airflow for Cooling
The power dissipated must be removed from the amplifier. This is best accomplished with
the use of a fan. Calculations for the required airflow for the fan are as follows.
Q
Q
CFM
m3/
=
min.
3.16×P
T
0.09×P
=
F
T
=
=
F
1.76×P
T
C
0.05×P
T
C
The equations shown give the required flow rate in CFM (cubic feet per minute) or m3per
minute). P is the amount of heat, in Watts, that must be dissipated. The constant in the
equations is obtained from the density of air (1.29 kg/m3) and the specific heat of air (930
J/kg/°C). The constant is then adjusted to provide results in the units desired.
Example:
R
= 1 ohm
load
V
= 27 volts
supply
I
load (max)
= 5 amps
PD=2×
I
×
load
V
suppl
−
I
×
R
load
load
PD= 220 Watts. If we allow the temperature of the amplifier to increase 20 °C, then we
have:
1.76×P
=
CFM
T
C
= 19.4 CFM, or 0.55 m3/min. Fans should be selected to achieve at least this airflow
Q
Q
CFM
rate. Most manufactures of fans have additional information that will help determine the
36 Power Amplifier Module User's Guide
Determining the Required Airflow for Cooling
optimal fan based on required flow rate and enclosure selection. The user should be careful
to understand that the fan will need to be mounted within the manufacturer's guidelines to
ensure that the specified airflow rate is achieved.
Note that the above example assumes a continuous DC signal. This assumes the worst case
possible. Typical applications will not require the output of a continuous DC current, and
the power dissipation of the amplifier can be adjusted accordingly.
Electrical Connections
The power amplifier module uses two different types of connector. The high power
connections required for the power supply and for the load connections are made using
terminal block connectors. Suitable types of connectors are shown below.
Description Manufacturer Supplier
Connector plug terminal
block, 2 position, 3.50mm
Connector plug terminal
block, 4 position, 3.500mm
Connector housing, 16
positions, 0.100 single row
Connector socket pins,
22-26AWG, crimp type. (16
pins required, maximum)
The other type of connector required are the pin header connectors. These connectors may
be assembled from components, or may be purchased pre-assembled. The spacing of the
pins is 2.54mm or 0.1”. Manufacturers of these components include AMP, Tyco and HRS.
Digi-key is one supplier of these components.
Configuration of the amplifier is done by way of shunts. The power amplifier module is
shipped with jumpers installed. However, in case additional jumpers are required, they may
be purchased from various manufacturers.
Weidmuller
1638780000
Weidmuller
1638800000
AMP / Tyco Electronics
2-87499-9
AMP / Tyco Electronics
1-87756-8
Digi-Key
281-1018-ND
Digi-Key
281-1020-ND
Digi-Key
A3025-ND
Digi-Key
A25966-ND
Power Amplifier Module User's Guide 37
Electrical Connections
Description Manufacturer Supplier
Shorting Jumpers 3M/ISD
929950-00
Digi-Key
929950-ND
Selecting a Power Supply
A power supply is required to provide electrical power to the amplifier. The size, type and
capacity of the power supply are highly dependent on the application.
Operating Voltage
The operating voltage of the power supply should be chosen to match the power
requirements of the intended load. This will allow the amplifier to provide the maximum
power to the load while minimizing the power that is dissipated by the amplifier itself.
Proper selection of the operating voltage will allow the amplifier to remain cool, and
minimize the cooling requirements.
For a load resistance of 2 ohms, requiring a maximum current of 4A, Ohm's Law shows that
the required voltage is 8 Volts. Since the minimum operating voltage is 27 volts, this
voltage should be used.
v=iR
Similarly, the maximum current that the power amplifier can supply may be limited by the
supply voltage to the amplifier, even if the power supply can supply the current. For
example, if the load is 8 ohms, and the supply voltage is 27 volts, the maximum current is
given by:
v
i
=
R
which in this case results in a maximum current of 3A.
This shows the theoretical minimum voltage required, and in practice should be raised by at
least 3 volts, to account for the overhead required by the amplifier. In addition, if the power
supply is located a significant distance from the amplifier, drops in the supply voltage may
become critical. In this case the voltage of the power supply will need to be even higher.
38 Power Amplifier Module User's Guide
Selecting a Power Supply
Current Handling Capability
The power supply chosen must be able to deliver the expected power to the load, plus some
additional power used by the amplifier itself. Typically, to use the amplifier at its fully rated
current ability, the power supply must be capable of delivering 10A continuous, minimum.
Additional capacity of the power supply will promote longer service life of the supply. In
most cases, a current handling capacity of 8A is sufficient.
In multiple amplifier configurations, the supply must be able to handle the requirements of
all amplifiers. This typically means that the required supply current is 8A times the number
of amplifiers present in the system. For example, with 4 amplifiers, the current capacity of
the power supply would need to be 32A, assuming that all 4 amplifiers would be required to
provide full power at any given moment.
Power Supply Type
The type of power supply selected – switching or linear, is up to the user. Either type of
power supply can be used with the power amplifier module. As long as the power
requirements are met, almost any type of supply can be used.
One important note is that isolated power supplies only should be used. Off-line type
switching supplies that have the secondary common with the primary may damage the
amplifier, and prove dangerous.
Only isolated-secondary type power supplies should be used with the power amplifier
module.
Connecting A Single Unit
A single amplifier can be connected as shown in figure 17. The figure shows the required
connection to make the amplifier work in a given system. Not the location of the system
ground in the figure. The amplifier uses a virtual ground point as a reference, and this
reference must be used as the system ground reference. Isolated secondary power supplies
are used, meaning the secondary or output of the power supply is isolated from the mains
supply.
Note that only the command input is a required input to the amplifier. The amplifier will
function without connection to the shutdown inputs. Current monitoring, current limiting,
and fault indication are all options available to the user, but do not necessarily need to be
connected. In addition, the gain selection jumper and the current / voltage mode jumper
must be installed for the amplifier to function.
Power Amplifier Module User's Guide 39
Connecting A Single Unit
User Equipment
Motor/
Load
Required Jumper Settings
Power Supply
Isolated Power Supply
Gain Selection Jumper
Amplifier
Module
GND Lug
Current/
Voltage
User System
Command Input
Current Monitor Output
Fault Indication
Current Limit Setting
Shutdown Inputs
User System GND
Common System GND
Figure 17. Single amplifier connections.
Connecting Multiple Units
Several amplifier units can be connected together to allow for multi-channel configurations.
In this setup, a common ground point is often required. The ground lug should be used for
this purpose. Figures 18 and 19 show two types of possible connections. Note that the
ground lug is used as the ground point for the common system ground reference.
40 Power Amplifier Module User's Guide
Connecting Multiple Units
Amplifier
Module
#1
Power Supply
Isolated Power Supply
Amplifier
Module
Figure 18. Multiple amplifiers connected with a single power supply.
#2
Common System GND
Amplifier
Module
#n
Power Amplifier Module User's Guide 41
Connecting Multiple Units
Amplifier
Module
#1
Power Supply
#1
Isolated Power Supply
Common System GND
Isolated Power Supply
Figure 19. Multiple power supplies to drive multiple power amplifiers.
Amplifier
Module
#2
Power Supply
#2
42 Power Amplifier Module User's Guide
Appendix A
Appendix A
Dimensions
The following pages show the mechanical drawings for the heatsink of the power amplifier
module. These drawings can be used in the fabrication of the enclosure of a mounting
fixture.
Power Amplifier Module User's Guide 43
Dimensions
44 Power Amplifier Module User's Guide
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