L9908 datasheet(76/152 Pages) STMICROELECTRONICS

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5.13.1.1

Conversion triggering logic

In order to improve the effectiveness of the A/D conversion and maximize the dynamic performances the current

monitor ADC implements two different conversion algorithms:

•

Up/Down TRK algorithm is active while SAR is disabled. TRK logic increments/decrements by 1LSB each

clock cycle the DAC input depending on the sign comparator assessment. This algorithm is able to

guarantee a high conversion accuracy but along with a limited input slew rate given by 1LSB/Tclk;

•

SAR algorithm is active while TRK is disabled. SAR logic increments/decrements by 210/2Nat each N clock

cycle. This algorithm is effective in the fast changing signal but lacks in accuracy.

A/D conversion default algorithm is TRK; SAR conversion algorithm is launched by triggering logic assessment.

Conversion triggering logic assessment follows two different criteria:

•

Command Edge Triggering;

•

Auto-triggering.

Note:

As long as enabled, each n-th A/D continuously converts input voltage into digital words: the conversion

triggering only defines how SAR and TRK algorithms interleave to get the most accurate current conversion.

5.13.1.1.1

Command edge triggering

Command Edge Triggering criteria relies on ACT function: when the value stored in ACTn register equals the

value configured in the TSYNCn register, a trigger pulse is generated and the SAR conversion is performed.

SAR conversion is launched at the same time on all current monitors, synchronously.

The n-th ACT to be used for sampling reference can be configured by means of the following bits:

Table 71. Command edge triggering configuration bits

CSM_SSPV_PH_CFG1

CSM_SSPV_PH_CFG0

Description

No synchronization

TSYNC based on Phase 1 (Default)

TSYNC based on Phase 2

TSYNC based on Phase 3

Note:

•

When CSM_SSPV_PH_CFG is set 00 the value output on CSOn and stored in CSn_READ correspond to

the last sample value when CSM_SSPV_PH_CFG ≠ 00.

•

When CSM_SSPV_PH_CFG = 01 ACT1 is used for the comparison

•

When CSM_SSPV_PH_CFG = 10 ACT2 is used for the comparison

•

When CSM_SSPV_PH_CFG = 11 ACT3 is used for the comparison

L9908

Functional description

DS13546 - Rev 5

page 76/152

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