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LTC2452

2452fb

APPLICATIONS INFORMATION

Figure 17 shows the measured LTC2452 INL vs Input

Voltage as a function of RS value with an input capacitor

CIN = 0.1μF.

In some cases, RScanbeincreasedabovetheseguidelines.

The input current is zero when the ADC is either in sleep

or I/O modes. Thus, if the time constant of the input RC

circuit

τ = RS • CIN, is of the same order of magnitude or

longer than the time periods between actual conversions,

then one can consider the input current to be reduced

correspondingly.

These considerations need to be balanced out by the input

signal bandwidth. The 3dB bandwidth ≈ 1/(2

πRSCIN).

Finally, if the recommended choice for CIN is unacceptable

for the user’s speciﬁc application, an alternate strategy is to

eliminate CIN and minimize CPAR and RS. In practical terms,

this conﬁguration corresponds to a low impedance sensor

directly connected to the ADC through minimum length

traces. Actual applications include current measurements

through low value sense resistors, temperature measure-

ments, low impedance voltage source monitoring, and so

on. The resultant INL vs VIN is shown in Figure 18. The

measurements of Figure 18 include a capacitor CPAR cor-

responding to a minimum sized layout pad and a minimum

width input trace of about 1 inch length.

Figure 17. Measured INL vs Input Voltage,

CIN = 0.1μF, VCC = 5V, TA = 25°C

Figure 18. Measured INL vs Input Voltage,

CIN = 0, VCC = 5V, TA = 25°C

DIFFERENTIAL INPUT VOLTAGE (V)

–5

2452 F17

–2

–6

–4

–8

–10

–3

–4

–1

–2

RS = 10k

RS = 2k

RS = 1k

RS = 0

CIN = 0.1μF

VCC = 5V

TA = 25°C

DIFFERENTIAL INPUT VOLTAGE (V)

–5

2452 F18

–2

–6

–4

–8

–10

–3

–4

–1

–2

RS = 10k

RS = 1k, 2k

RS = 0

CIN = 0

VCC = 5V

TA = 25°C

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