MAX17843ACB datasheet(32/131 Pages) MAXIM

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Acquisition Mode

The host enters the acquisition mode by writing a logic-one

to the SCAN bit in the SCANCTRL register. This write is

actually an automatic strobe of the bit since SCAN always

reads logic-zero. In daisy-chained devices, acquisitions

in upstack devices are delayed by the propagation delay

(tPROP) of the command packet through each device.

The acquisition is complete when the device sets the

SCANDONE bit. The basic acquisition process is outlined

below with a detailed flowchart in Figure 8:

1) Disable HV charge pump.

2) VBLKP conversion, if enabled.

3) All enabled cell conversions (first):

a. Ascending order (1:12) if pyramid mode, or

b. Descending order (12:1) if top-down mode.

4) All enabled cell conversions (second):

a. Descending order (12:1).

5) VBLKP conversion (second), if enabled.

6) Diagnostic conversion (first), if enabled.

7) Diagnostic conversion (second), if enabled.

8) Enable HV charge pump for recovery period unless:

a. OVSAMP[2:0] = 0 (no oversampling), or

b. All oversample measurements are complete.

9) Repeat steps 1–8 until all oversamples are done.

10) All enabled auxiliary conversions, in ascending order

(AUXIN1, AUXIN2).

11) Set SCANDONE bit.

Oversampling

Oversampling mode performs multiple measurement

cycles in a single acquisition, and averages the samples

in the ALU to reduce the measurement noise and effec-

tively increase the resolution of each measurement result.

In oversampling mode, acquisition times are proportional

to the number of oversamples, as shown in Table 8. The

number of oversamples can be configured from 4 to 128

by OVSAMPL[2:0], as shown in Table 7. The AUXIN mea-

surements are never oversampled, even in oversampling

mode.

To add n bits of measurement resolution requires at least

22n oversamples. Since the ADC resolution is 12 bits,

13-bit resolution requires at least 4 oversamples and to

achieve the maximum 14-bit resolution requires at least

16 oversamples; therefore, with no oversampling, only

the higher 12 bits of the measurement are statistically

significant and with 4 or 8 oversamples, only the higher

13 bits are statistically significant. Taking more than 16

oversamples further reduces the measurement variation.

Of course with no oversampling, measurements can be

averaged externally to achieve increased resolution, but

at a higher computational cost for the host.

Table 7. Oversampling

OVSAMPL[2:0]

OVERSAMPLES

THEORETICAL RESOLUTION

ACQUISITION WATCHDOG TIMEOUT

000b (default)

12 bits

1.10ms

001b

13 bits

2.08ms

010b

13 bits

3.36ms

011b

14 bits

5.92ms

100b

14 bits

10.99ms

101b

14 bits

21.18ms

110b

128

14 bits

41.56ms

111b

128

14 bits

41.56ms

MAX17843

12-Channel, High-Voltage Smart Sensor

Data-Acquisition Interface

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MAX17843ACB Datasheet(PDF) 32 Page - Maxim Integrated Products

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