LMP8481MM-SSLASHNOPB datasheet(15/29 Pages) TI1

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LMP8480, LMP8481

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SNVS829C – MARCH 1999 – REVISED SEPTEMBER 2015

Feature Description (continued)

8.3.4.2 Setting Output to One-Half VCC or external VREF

For mid-range operation VREFB should be tied to ground and VREFA can be tied to VCC or an external A/D

reference voltage. The output will be set to one-half the reference voltage. For example, a 5-V reference would

result in a 2.5-V output “zero” reference.

Figure 25. Applying a Divided Reference Voltage

VREF’ = (VREFA – VREFB) / 2

(7)

When the reference pins are biased at different voltages, the output will be referenced to the average of the two

applied voltages.

The reference pins should always be driven from clean, stable sources, such as A/D reference lines or clean

supply lines. Any noise or drifts on the reference inputs are directly reflected in the output. Take care if the power

supply is used as the reference source so as to not introduce supply noise, drift or sags into the measurement.

It is possible to set different resistor divider ratios by adding external resistors in series with the internal 100-K

resistors, though the temperature coefficient (tempco) of the external resistors may not tightly track the internal

resistors and there will be slight errors over temperature.

The LMP8480 is identical to the LMP8481, except that both the VREF pins are grounded internally. The LMP8481

can replace the LMP8480 if both VREF pins are grounded.

8.3.5 Reference Input Voltage Limits (LMP8481 Only)

The maximum voltage on either reference input pin is limited to VCC or 12 V, whichever is less.

The average voltage on the two VREF pins, and thus the actual output reference voltage level, is limited to a

maximum of 1.5 V below VCC, or 6 V, whichever is less. Beware that supply voltages of less than 7.5 V will have

a diminishing VREF maximum.

Both VREFA and VREFB may both be grounded to provide a ground referenced output (thus functionally duplicating

the LMP8480).

It should be noted that there can be a dynamic error in the VREF to output level matching of up to 100 µV/V.

Normally this is not an issue for fixed references, but if the reference voltage is dynamically adjusted during

operation, this error needs to be taken into account during calibration routines. This error will vary in both

amplitude and polarity part-to-part, but the slope will generally be linear.

8.3.6 Low-Side Current Sensing

The LMP8480 and LMP8481 are not recommended for low-side current sensing at ground level. The voltage on

either input pin must be a minimum of 4.0 V above the ground pin for proper operation. The output level may not

be valid for common-mode voltages below 4 V. This should be taken into consideration for monitoring or

feedback applications where the load-supply voltage may dip below 4 V or be switched completely off.

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