PS081 datasheet(55/155 Pages) AMSCO

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3-32

PSØ81

The delay depends on the value of the low-pass capacitor which is parallel to the collector resistor of

the comparator transistor. We recommend 3.3 kOhm for the collector resistor and 3.3 nF for the

parallel capacitor. If this capacitor is changed, the optimum Mult_PP factor changes, too. This is the

main dependency of Mult_PP from the hardware, besides the general selection between external and

internal comparator.

Optimizing Gain Drift with Mult_PP

With our hardware recommendations the system has a remaining gain error of approximately

8 ppm/K if Mult_PP is set to 1.0 or not used. This remaining gain error can be reduced to < 1 ppm

by choosing the right Mult_PP factor.

Once established during the development phase, this value can be used for the whole series produc-

tion. It is definitely not necessary to adjust every single electronic.

Note:

The gain drift of the PS081 itself is very close to zero. The remaining gain drift comes mainly from

the nonlinear part of the delay time of the comparator. This nonlinear part itself results mainly from

the low-pass filter behind the first stage of the comparator (3.3 kOhm || 3.3 nF). It can be significant-

ly reduced by the Mult_PP value. Because the low pass filter can be reproduced very accurately also

the compensation is very stable over production and needs no adjustment.

With the recommended hardware we determined following Mult_PP factors:

Wheatstone bridge with external comparator and analog mux TS5A3160 (TI) :

1.28

Wheatstone bridge with external comparator and analog mux 74LVC1G3157(TI) :

1.14

PICOSTRAIN standard wiring, external comparator, our recommended values:

1.28

For Wheatstone Mode we recommend TS5A3160 because it has a good behavior also at lower sup-

ply voltages < 2.7 V, but 74LVC1G3157 is a good choice, too, for supply voltages of 3.0 V or higher.

If own hardware settings are used, especially if the low pass filter is changed, the MULT_PP factor

may change and has to be determined. The value for this hardware setting is valid for the whole pro-

duction and is independent from production batches. For more details see application note AN018.

3.6.6

Zero Drift of PS081 itself

Also the zero drift of the PS081 originates from a reason other than the drift of an AD-Converter.

The reason of the remaining zero drift of our PICOSTRAIN products are parasitic resistor paths that

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PS081 Datasheet(PDF) 55 Page - ams AG