INA333-HT datasheet(14/24 Pages) TI

14 / 24 page

SBOS514 – MARCH 2010

www.ti.com

APPLICATION INFORMATION

Application

information

below

provided

for

SETTING THE GAIN

commercial temperature as a reference and not for

high temperature.

Gain of the INA333 is set by a single external

resistor, RG, connected between pins 1 and 8. The

It is not recommonded to use gain < 100 for the high

value of RG is selected according to Equation 1:

temperature (210°C) application. A filter is needed

between Pin 1 and Pin 9 for gain = 100 and

G = 1 + (100 k

Ω/RG)

(1)

gain = 1000 in 210°C application. Recommended

Table 2 lists several commonly-used gains and

resistor value is 3.5 k

Ω and capacitor value is 10 nF.

resistor values. The 100 k

Ω term in Equation 1

Figure 34 shows the basic connections required for

comes from the sum of the two internal feedback

operation of the INA333. Good layout practice

resistors of A1 and A2. These on-chip resistors are

mandates the use of bypass capacitors placed close

laser trimmed to accurate absolute values. The

to the device pins as shown.

accuracy

and

temperature

coefficient

these

resistors are included in the gain accuracy and drift

The output of the INA333 is referred to the output

specifications of the INA333.

reference

(REF)

terminal,

which

normally

grounded. This connection must be low-impedance to

The stability and temperature drift of the external gain

assure good common-mode rejection. Although 15

Ω

setting resistor, RG, also affects gain. The contribution

or less of stray resistance can be tolerated while

of RG to gain accuracy and drift can be directly

maintaining specified CMRR, small stray resistances

inferred from the gain Equation 1. Low resistor values

of tens of ohms in series with the REF pin can cause

required for high gain can make wiring resistance

noticeable degradation in CMRR.

important. Sockets add to the wiring resistance and

contribute additional gain error (possibly an unstable

gain error) in gains of approximately 100 or greater.

To ensure stability, avoid parasitic capacitance of

more than a few picofarads at the RG connections.

Careful matching of any parasitics on both RG pins

maintains optimal CMRR over frequency.

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