L9908 datasheet(88/152 Pages) STMICROELECTRONICS

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5.13.3.1

Analog format current information

Current Measurement reconstruction formula at CSO_n pin is the following:

ILOADRsℎunt= VCSO_n

ΔCM_out_LSB−OFSΔCM_in_LSB

(19)

Where: VCSO_n is the voltage at pin CSO_n, OFS is the selected shift value, RSHUNT is the shunt resistance

value, ∆CM_in_LSB is the input ADC quantization step, defined in Table 75, and ∆CM_out_LSB is D/A quantization

step, available in Table 79 (parameter name: T CM_out_dac_lsb).

Example:

•

VCSO_n = 1 V

•

CSMn_OFS = 1024LSB

•

CSM_OUT_RANGE_CFG = 0

•

CSM_OUT_RANGE_CFG = 0

•

CS_INRANGE_CFG = 011 (CM input ADC range +/-90 mV)

•

ILOAD*RSHUNT = (1/1.611 mV - 1024)*100.7 μV = -40.609 mV

Latency associated to analog format current information update in auto-triggering mode can be retrieved in the

following table.

Table 80. Current monitors A/D - D/A auto-triggering latency

Symbol

Parameter

Min

Typ

Max

Unit

Notes

CM_latency

CM latency

Tclk

Application information(1)

1. CSMn_SYNC_COUNT_CFG1 (16/24/32/40 Tclk) + SAR (10 Tclk) + DSP (7 to 19 Tclk)

Note:

Please note that values indicated in Table 80 refers to ADC & DSP section only. CSO buffer settling time should

be added to retrieve the full chain settling time at CSOn.

5.13.4

Current monitor A/D - D/A chain

When Current Measurement is evaluated at CSOn pins, the full A/D-D/A chain is exploited and the structure can

be assimilated to a voltage amplifying stage, which can be represented as in the following picture, and the

corresponding Input/Output transfer function:

Figure 64. A/D-D/A chain accuracy block diagram

VCSO=VING±VCM_in_total_errorG+VOFS±VCM_out_total_error

(20)

CSM chain gain values are summarized in the following table.

L9908

Functional description

DS13546 - Rev 5

page 88/152

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