AN143.0

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X3100 Voltage Measurement Accuracy

Description

This test measures the accuracy of the celll voltage

measurement circuits of the X3100. In the test, a known

voltage is applied across each cell input of the X3100. The

analog output voltage of the X3100 is measured for each

cell. This value is compared to the input voltage. The

collected data includes the values from three devices from

three different lots. The data also includes tests at 0°C, 25°C

and 50°C.

Test Setup

For this test, Vcc was held at 16V to prevent the device

entering the sleep mode when testing cell voltages below

2V. In the test 4V was applied to all cells, except the cell

being measured. The voltage was applied at 10mV intervals

over four ranges. These input ranges were 1.5 to 1.7V, 2.5 to

2.7V, 3.5 to 3.7V and 4.0 to 4.2V.

For each cell and each applied voltage the output was

recorded. This involves the changing of the analog

multiplexer setting in the X3100. In gathering the data with

this test, the output was sample. This procedure was used to

reduce the effect of external noise on the test environment.

Results

The data for this test is available in raw form in an Excel

spreadsheet. This spreadsheet includes data for each

device, data for each lot, and data for all devices. Each set of

data includes results for the three temperature settings and

the four gain settings. The data was copied to other files for

the purposes of generating graphs.

The result summaries show the output error as a

percentage. This error is provided for each of 3 lots as well

as the combined data. Data is averaged, and standard

deviation computed, from samples taken at three

temperatures 0°C, 25°C and 50°C.

On the following charts, absolute error is the Output minus

the Input, while the percent error is calculated as follows:

Overall Performance

The following set of graphs shows the performance of the

X3100 over temperature and across three lots of three

devices. The graphs will show the basic input/output curve,

raw error, and error after correction for offset and gain.

The below data shows that the X3100 output is accurate,

with 3 standard deviations, to better than 2.5% error across

all measured voltages. It also shows that over the key range

of 2.5 to 4.2V, accuracies of better than 1% can be expected.

These accuracies are not dependent on any calibration

factors.

X3100

16V

VCELL1

VCELL2

VCELL3

VCELL4

VSS

Error

Output Input–

Input

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Application Note May 9, 2005

FIGURE 1. CELL VOLTAGE MEASUREMENT