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LSAMP Offset Diagnostic Measurement

The LSAMP diagnostic measurement (DIAGSEL[2:0] =

0b011) measures the level-shift amplifier offset by short-

ing the LSAMP inputs during the diagnostic portion of the

acquisition. The result is available in the DIAG register

after a normal acquisition. For this measurement, the

ADC polarity is automatically set to bipolar mode to allow

accurate measurement of voltages near zero. This mea-

surement eliminates the chopping phase to preserve the

offset error. If the diagnostic measurement exceeds the

valid range for VOS_LSAMP, as specified in the Electrical

Characteristics table, the chopping function may not be

able to cancel out all the offset error, and the acquisition

accuracy could be degraded accordingly. See Figure 39

for LSAMP Offset Diagnostics

The LSAMP offset is computed from the result in the

DIAG register, as follows:

LSAMP Offset = ( | DIAG[15:2] - 2000h |/16384d ) x 5V

The validity of measurements through LSAMP is further

confirmed by the ALTREF and VAA diagnostics, and com-

parison of the VBLKP measurement to the sum of the cell

measurements.

Zero-Scale ADC Diagnostic Measurement

Stuck ADC output bits can be verified with a combination

of the zero-scale and full-scale diagnostics. The zero-

scale ADC diagnostic measurement (DIAGSEL[2:0] =

0b100) verifies that the ADC conversion results in 000h

when its input is at -VAA in bipolar mode (since for an

input ≤ -2.5V, DIAG[15:0] = 0000h). For this measure-

ment, the ADC is automatically set to bipolar mode (see

Figure 40).

Figure 39. LSAMP Offset Diagnostic

Figure 40. ADC Zero-Scale Diagnostic

LSAMP

HVMUX

BUS

ADC IN -

ADC IN +

MUX

ADC

ADC AUTOMATICALLY

IN BIPOLAR MODE

G = 6/13

ADC IN -

ADC IN +

MUX

ADC

REF

THRM

AGND

VAA

AGND

ADC AUTOMATICALLY

IN BIPOLAR MODE

MAX17843

12-Channel, High-Voltage Smart Sensor

Data-Acquisition Interface

www.maximintegrated.com

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