PAD38 – Rev B
- HIGH VOLTAGE – 200 VOLTS
- HIGH CURRENT – 10 AMPS
- 125 WATT DISSIPATION CAPABILITY
- HIGH SLEW RATE- 10V/µS
- FOUR WIRE CURRENT LIMIT
- OPTIONAL BOOST VOLTAGE INPUTS
- LINEAR AND ROTARY MOTOR DRIVE
- YOKE/MAGNETIC FIELD EXCITATION
- PROGRAMMABLE POWER SUPPLIES
- INDUSTRIAL (PA) AUDIO
The PAD38 is a power operational amplifier constructed with surface mount components to provide a cost effective solution for many industrial applications With a footprint only 3.3in2 the PAD38 offers outstanding performance that rivals more expensive hybrid component amplifiers or rack-mount amplifiers. User selectable external compensation tailors the amplifier’s response to the application requirements. Programmable current limit is builtin. The amplifier circuitry is built on a thermally conductive but electrically insulating substrate. No BeO is used in the PAD38. The resulting module is a small, high performance solution for many industrial applications.
CIRCUIT & CONNECTIONS
PINOUT & CONNECTIONS
ABSOLUTE MAXIMUM RATINGS SPECIFICATIONS
- Unless otherwise noted: TC = 25OC, compensation Cc = 470pF, DC input specifications are ± value given, power supply voltage is typical rating.
- Derate internal power dissipation to achieve high MTBF.
- Doubles for every 10OC of case temperature increase.
- +Vs and −Vs denote the positive and negative supply voltages to the output stage. +VB and −VB denote the positive and negative supply voltages to the
- Rating applies if the output current alternates between both output transistors at a rate faster than 60Hz.
- Power supply voltages +VB and −VB must not be less than +Vs and −Vs respectively. Total voltage +VB to −VB 240V maximum.
- The PAD38 is constructed with MOSFET transistors and ESD handling procedures must be observed.
The operating voltages of the PAD38 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.
The current limiting function of the PAD38 is a versatile circuit that can be used to implement a four-wire current limit configuration. The four-wire current limit configuration insures that parasitic resistance in the output line, Rp, does not affect the programmed current limit setting. See Figure 1 below. The sense voltage for current limit is 0.7V. Thus:
Where IL is the value of the limited current and RS is the value of the current limit sense resistor.
In addition, the sense voltage has a temperature coefficient approximately equal to –2.2mV/℃.
MOUNTING THE 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 PAD38 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.
The PAD38 must be phase compensated. The compensation capacitor, CC, is connected between pins 4 and 6. The compensation capacitor must be an NPO type capacitor rated for the full supply voltage (200V). 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 100pF is not recommended.
USING THE IQ PIN FUNCTION
When pin 25 (IQ) is tied to pin 6 (Cc1) the class AB bias of the output stage becomes C bias. The quiescent current of the PAD38 typically drops by 10mA. In some applications the reduced quiescent current is important. However, note that applying this option will raise the output impedance of the amplifier which may change the stability of the circuit and will increase crossover distortion also.
The small signal stages of the PAD38 are connected to the ±VB power supply pins. When the ±VB voltages are greater than the ±Vs power supply pins the small signal stages of the amplifier are biased so that the output transistors can be driven very close to the ±Vs rails. Close swings to the supply rails increase the efficiency of the amplifier and make better use the supply voltages. This technique is often used to operate the amplifier with only a single high current power supply, thus reducing the system size and cost. Also see the application article AN-22 Single Supply Operation with Power Op Amps for more detailed information and circuits.