100V 10A 75W Compact Single Supply Op Amp

PAD141 – Rev D

DESCRIPTION

The PAD141 compact single supply power op amp is constructed with surface mount components to provide a cost effective solution for many industrial applications. With a footprint only 40mm square the PAD141 offers outstanding performance that rivals more expensive hybrid components. An integrated heat sink and fan cooling are included. User selectable external compensation tailors the amplifier’s response to the application requirements. The input common mode range includes ground making the PAD141 suitable for applications with a single supply voltage. The output voltage can swing to within 1V of the negative supply voltage (usually ground) at 10A output. The PAD141 is built on a thermally conductive but electrically insulating substrate. No BeO is used in the PAD141. For custom applications the PAD141-1 version of the amplifier is available without the integrated heat sink and fan. RoHS Compliant.

A NEW CONCEPT

A critical task in any power amplifier application is cooling the amplifier. Until now component amplifier manufacturers often treated this task as an after-thought, left for the user to figure out. At Power Amp Design the best heat sink and fan is chosen at the start and becomes an integral part of the overall amplifier design. The result is the most compact and volumetric efficient design combination at the lowest cost. In addition, this integrated solution concept offers an achievable real-world power dissipation rating, not the ideal rating usually cited when the amplifier case is somehow kept at 25℃. The user no longer needs to specify, procure or assemble separate components.

CIRCUIT & CONNECTIONS

EQUIVALENT CIRCUIT

PINOUT & CONNECTIONS

ABSOLUTE MAXIMUM RATINGS SPECIFICATIONS

NOTES:

1. Unless otherwise noted: T_C = 25℃, compensation C_c = 470pF, DC input specifications are ± value given, power supply voltage is typical rating.
2. Derate internal power dissipation to achieve high MTBF.
3. Doubles for every 10℃ of case temperature increase.
4. +V_s and −V_s denote the positive and negative supply voltages to the output stage. +V_cc and –V_cc denote the positive and negative supply voltages to
   the small signal stages. +V_cc and –V_cc may not be more than + and – 20V greater than +V_s and –V_s respectively.
5. Limited by fan characteristics. During operation, even though the heat sink may be at 85OC the fan will be at a lower temperature.
6. Rating applies if the output current alternates between both output transistors at a rate faster than 60Hz.
7. Power supply voltages +V_cc and −V_cc must not be less than +Vs and −Vs respectively. Total voltage +V_cc to −V_cc 100V maximum.
8. L10 refers to the time it takes for 10% of a population of fans to fail. Lower ambient temperature increases fan life.
9. Specifications for the PAD141-1 are the same as for the PAD141 except as shown in this column.

OPERATING CONSIDERATIONS

SAFETY FIRST

The operating voltages of the PAD141 are potentially deadly. When developing an application circuit it is wise to begin with power supply voltages as low as possible while checking for circuit functionality. Increase supply voltages slowly as confidence in the application circuit increases. Always use a “hands off” method whereby test equipment probes are attached only when power is off.

SINGLE SUPPLY OPERATION

Although the PAD141 easily operates with dual power supplies, as is usually the case with operational amplifiers, it is designed to operate just as easily with a single positive supply voltage. The input common mode range actually extends 4V beyond the negative supply voltage and the output can swing within 1V of the negative supply voltage (usually ground) at 10A of output current and will actually reach 0V at zero output current. See Figure 2 in Application Circuits on page 10 for a typical connection.

COOLING FAN

The PAD141 relies on its fan for proper cooling of the amplifier. Make sure that air flow to the fan and away from the heat sink remains unobstructed. The cooling method used is impingement cooling, which means that cool air is pushed into the heat sink and warm air is exhausted through the spaces between the heat sink fins. To eliminate electrical noise created by the cooling fan we recommend a 47µF capacitor placed directly at the point where the fan wires connect to the PCB. See application note AN-24 for further details.

MOUNTING THE AMPLIFIER

The amplifier is supplied with four 4-40 M/F hex spacers at the four corners of the amplifier. Once the amplifier is seated, secure the module with the provided 4-40 nuts and torque to 4.7 in lb [53 N cm] max. See “Dimensional Information” for a detailed drawing. It is recommended that the heat sink be grounded to the system ground. This can easily be done by providing a grounded circuit board pad around any of the holes for the mounting studs.

MOUNTING THE PAD141-1 AMPLIFIER

In most applications the amplifier must be attached to a heat sink. Spread a thin and even coat of heat sink grease across the back of the PAD141 and also the heat sink where the amplifier is to be mounted. Push the amplifier into the heat sink grease on the heat sink while slightly twisting the amplifier back and forth a few times to bed the amplifier into the heat sink grease. On the final twist align the mounting holes of the amplifier with the mounting holes in the heat sink and finish the mounting using 4-40 hex male-female spacers. Mount the amplifier to the mother board with 4-40 X 1/4” screws. For all mounting hardware torque to 4.7 in lb [53 N cm] max.

CURRENT LIMIT

The current limiting function is connected as shown in Figure 1. It is best to connect Rs directly to OUT to avoid any significant parasitic resistance, Rp, as shown in Figure

1. The sense voltage for current limit is approximately
   0.65V. Thus:

Where I_L is the value of the limited current and R_S is the value of the current limit sense resistor.
In addition, the sense voltage has a temperature coefficient approximately equal to –2.2mV/℃.

PHASE COMPENSATION

The PAD141 must be phase compensated. The compensation capacitor, C_C, is connected between pins 2 and 3. The compensation capacitor must be an NPO type capacitor rated for the full supply voltage (100V). On page 2, under Amplifier Pinout and Connections, you will find a table that gives recommended compensation capacitance value for various circuit gains and the resulting slew rate for each capacitor value. Consult also the small signal response and phase response plots for the selected compensation value in the Typical Performance Graphs section. A compensation capacitor less than 47pF is not recommended.

TYPICAL PERFORMANCE GRAPHS

SAFE OPERATING AREA

DIMENSIONAL INFORMATION

APPLICATION CIRCUITS