Features

● Ultra -low bias current: maximum 100FA

● Low offset: maximum 2mv

● Low drifting: maximum 10 μV/° C

● High open ring gain: minimum 94db

● Low noise: 15nv/√Hz

● Plastic impregnation and other packaging

Application

● Optoelectronics detector front placed large device

● chromatography method

● Static electricity meter

● mass spectrometer

● PH probe amplifier

] ● ion meter measurement

Explanation

OPA129 is an ultra-low bias current single-chip operational amplifier, which is encapsulated with 8 pad PDIP and SO-8. Using advanced geometric medium insulation field effects transistor (DIFET #174;) input, this single -piece amplifier achieves high performance levels.

The manufacturing of DIFET eliminates the leakage current, which is the main contributor to the traditional single -chip FET input bias current. This can reduce the input bias current by 10 to 100 times. It can achieve very low input bias current without the need to rely on small -sized FET or CMOS design. These designs may be affected by greater bias voltage, voltage noise, drift and poor power suppression.

OPA129 special pin eliminates the leakage current that occurs with other computing amplifiers. There are no internal connections in pin 1 and 4, even if the package is installed on the surface, the circuit board is allowed to protect the traces of the circuit board.

OPA129 has 8-needle DIP and SO packaging, which is stipulated at the temperature of -40 ° C to+85 ° C.

Simplified circuit

Typical performance curve

TA u003d+25 ° C,+15VDC, unless otherwise explained.

Application information

Non -standard pins

OPA129 Use non -standard pins to achieve low input bias current as possible. The negative power supply is connected to the pin 5-see Figure 1. This is to reduce the leakage current of the input terminal of the computing amplifier from the Power (the pins of the traditional computing amplifier 4) to the computing amplifier. With this new pin, the sensitive input is separated from the two power supply feet.

The bias voltage is fine -tuned

OPA129 does not have a traditional bias distribution connection. The pin of the input next to the critical reversal 1No internal connection. This eliminates the leakage current source and allows protecting the input terminal. The pin 1 near the two input pins and the pin 4 of the pin 4 have no internal connection. This allows an optimized circuit board layout and protection of the circuit board layout.

Because of its laser fine -tuning input level, most applications do not require external bias voltage fine -tuning. If you need to repair the edge, you can use the circuit shown in Figure 1. The power supply voltage is decomposed, filtered, and is applied to non -inverse input. The circuit shown is very sensitive to changes in the power supply voltage. If necessary, you can increase supervision.

Protection and shielding

Ultra -low input bias current transportation amplifier needs to take preventive measures to achieve the best performance. The leakage current on the surface of the circuit board will exceed the input bias current of the amplifier. For example, the circuit board resistance from the power pins to the input pin is 1012 and the current is 15Pa, which is more than 100 times the computing amplifier input current.

In order to reduce surface leakage, the protection line should be completely surrounded by input terminals and other circuits connected to the computing amplifier input terminal. DIP packaging should have protection marks on both sides of the circuit board. The protective ring should be driven by the circuit node with equal input potential input with the computing amplifier, as shown in Figure 2. The substrate, pin 8, should also be connected to the protective cover of the circuit board to ensure that the amplifier is completely surrounded by the protective potential. This can minimize the leakage current and noise pickup.

Be careful to shield it to reduce noise pickup. Blinds near the feedback element will also help reduce noise pickup.

The friction electrical effect (the charge generated by friction) may be a source of trouble. The vibration of circuit boards, input connectors and input cables can cause noise and drift. Make the component as strong as possible. Connect the cable to avoid movement and vibration. Special low noise or low leakage cables help reduce noise and leakage current. Keep all input connections as short as possible. Surface installation elements can reduce the size of the circuit board and allow more rigid assembly.

Circuit plate layout

OPA129 uses a new pin to ultra -low input bias current. There are no internal connections in needle 1 and pin 4. This makes the circuit board have enough space to install a protective ring around the computing amplifier input pin. Figure 3 shows the recommended circuit board layout. As shown in the figure, the protective ring should be connected to the sales 8 (substrate). It should be driven by a circuit node with equal input -end potential as the computing amplifier. For common circuit configuration, see Figure 2.

Test

Due to the high performance of OPA129, it is very difficult to accurately test OPA129. Ordinary testing equipment may not be able to analyze the extremely low bias current of the amplifier.

Inaccurate bias current measurement may be due to:

1. Test plugLeakage.

2. Uninterrupted package.

3. Humidity or dew point condensate.

4. Control of fingerprints or anti -static treatment of chemicals.

5. Test environmental temperature.

6. Load power consumption.

7. Mechanical stress.

8. Static and electromagnetic interference.