TL05X_08 datasheet(42/67 Pages) STMICROELECTRONICS

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TL05x, TL05xA

ENHANCED-JFET LOW-OFFSET

OPERATIONAL AMPLIFIERS

SLOS178A – FEBRUARY 1997 - REVISED FEBRUARY 2003

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

precision constant-current source over temperature

A precision current source (see Figure 85) benefits from the high input impedance and stability of Texas

Instruments enhanced-JFET process. A low-current shunt regulator maintains 2.5 V between the inverting input

and the output of the TL05x. The negative feedback then forces 2.5 V across the current-setting resistor R;

therefore, the current to the load simply is 2.5 V divided by R.

Possible choices for the shunt regulator include the LT1004, LT1009, and LM385. If the regulator’s cathode

connects to the operational amplifier output, this circuit sources load current. Similarly, if the cathode connects

to the inverting input, the circuit sinks current from the load. To minimize output current change with temperature,

R should be a metal film resistor with a low temperature coefficient. Also, this circuit must be operated with

split-voltage supplies.

150 pF

+15 V

–15 V

100 k

Ω

Load

V = 0 to 10 V

(a) SOURCE CURRENT LOAD

(b) SINK CURRENT LOAD

V = 0 to –10 V

Load

–15 V

+15 V

150 pF

100 k

Ω

NOTE A: U1 = 1/2 TL05x

U2 = LM385, LT1004, or LT1009 voltage reference

I =

2.5 V

, R = Low-temperature-coefficient metal-film resistor

Figure 85. Precision Constant-Current Source

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