Capacitive Loads

The LM20EP handles capacitive loading well. Without any

precautions, the LM20EP can drive any capacitive load less

than 300 pF as shown in Figure 4. Over the specified tem-

perature range the LM20EP has a maximum output imped-

ance of 160

Ω. In an extremely 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

bypass the power supply voltage, as shown in Figure 5.Ina

noisy environment it may even be necessary to add a ca-

pacitor from the output to ground with a series resistor as

shown in Figure 5. A 1 µF output capacitor with the 160

Ω

maximum output impedance and a 200

Ω series resistor will

form a 442 Hz lowpass filter. Since the thermal time constant

of the LM20EP is much slower, the overall response time of

the LM20EP will not be significantly affected.

SC70-5

SC70-5

no heat sink

small heat sink

θ

JA

T

θ

JA

T

(˚C/W)

(˚C)

(˚C/W)

(˚C)

Still air

412

0.2

350

0.19

SC70-5

SC70-5

no heat sink

small heat sink

θ

JA

T

θ

JA

T

(˚C/W)

(˚C)

(˚C/W)

(˚C)

Moving air

312

0.17

266

0.15

See Figure 1 for PCB layout samples.

micro SMD

micro SMD

no heat sink

small heat fin

θ

JA

T

θ

JA

T

(˚C/W)

(˚C)

(˚C/W)

(˚C)

Still air

340

0.18

TBD

TBD

micro SMD

micro SMD

no heat sink

small heat fin

θ

JA

T

θ

JA

T

(˚C/W)

(˚C)

(˚C/W)

(˚C)

Moving air

TBD

TBD

TBD

TBD

FIGURE 3. Temperature Rise of LM20EP Due to

Self-Heating and Thermal Resistance (

θ

20099915

FIGURE 4. LM20EP No Decoupling Required for

Capacitive Loads Less than 300 pF.

R(

Ω)

C (µF)

200

1

470

0.1

680

0.01

1 k

0.001

20099916

20099933

FIGURE 5. LM20EP with Filter for Noisy Environment and Capacitive Loading greater than 300 pF. Either placement

of resistor as shown above is just as effective.

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