2.0 Capacitive Loads

The LM61 handles capacitive loading well. Without any spe-

cial precautions, the LM61 can drive any capacitive load as

shown in

Figure 4. Over the specified temperature range the

LM61 has a maximum output impedance of 5 k

Ω.Inanex-

tremely noisy environment it may be necessary to add some

filtering to minimize noise pickup. It is recommended that

0.1 µF be added from +V

ply voltage, as shown in

Figure 5. In a noisy environment it

may be necessary to add a capacitor from the output to

ground. A 1 µF output capacitor with the 5 k

Ω maximum out-

put impedance will form a 32 Hz lowpass filter. Since the

thermal time constant of the LM61 is much slower than the 5

ms time constant formed by the RC, the overall response

time of the LM61 will not be significantly affected. For much

larger capacitors this additional time lag will increase the

overall response time of the LM61.

SOT-23*

SOT-23**

TO-92*

TO-92***

no heat sink

small heat fin

no heat sink

small heat fin

θ

JA

T

θ

JA

T

θ

JA

T

θ

JA

T

(˚C/W)

(˚C)

(˚C/W)

(˚C)

(˚C/W)

(˚C)

(˚C/W)

(˚C)

Still air

450

0.26

260

0.13

180

0.09

140

0.07

Moving air

180

0.09

90

0.05

70

0.03

*Part soldered to 30 gauge wire.

Figure 2.

***Part glued and leads soldered to 1

″ square of 1/16″ printed circuit board with 2oz. foil or similar.

FIGURE 3. Temperature Rise of LM61 Due to

Self-Heating and Thermal Resistance (

θ

DS012897-15

FIGURE 4. LM61 No Decoupling Required for

Capacitive Load

DS012897-16

FIGURE 5. LM61 with Filter for Noisy Environment

DS012897-17

FIGURE 6. Simplified Schematic

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