TMCS1100A2 datasheet(16/35 Pages) TI1

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TMCS1100

SBOS820 – SEPTEMBER 2019

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Feature Description (continued)

9.3.5 Current-Sensing Measurable Ranges

The TMCS1100 can be configured to allow for bidirectional or unidirectional measurable current ranges based on

the external voltage on the VREF pin. The output voltage is a first-order linear function of the input current, as

shown in Equation 1, and is only limited by VOUT swing to either supply or ground. Linear output swing range to

both VS and GND is calculated by equations Equation 11 and Equation 12.

VOUT,max = VS – SwingVS

(11)

VOUT,min = SwingGND

(12)

Rearranging the transfer function of the device to solve for input current, and substituting VOUT,max and VOUT,min

yields the maximum and minimum measurable input current ranges as shown in Equation 13 and Equation 14.

IIN,MAX+ = (VOUT,max – VREF) / S

(13)

IIN,MAX- = (VREF – VOUT,min) / S

where

•

IIN,MAX+ is the maximum linear measurable positive input current.

•

IIN,MAX- is the maximum linear measurable negative input current.

•

S is the sensitivity of the device variant.

(14)

Setting VREF to the middle of the output swing range provides bidirectional measurement capability, whereas

setting VREF close to the ground provides a unidirectional measurement. Custom ranges with nonuniform positive

and negative input current ranges can be achieved by appropriately scaling the VREF potential relative to the full

output voltage range.

9.4 Device Functional Modes

9.4.1 Power-Down Mode

As a result of the inherent galvanic isolation of the device, very little consideration must be paid to powering

down the device, as long as the limits in the Absolute Maximum Ratings table are not exceeded on any pins. The

isolated current input and the low-voltage signal chain can be decoupled in operational behavior, as either can be

energized with the other shut down, as long as the isolation barrier capabilities are not exceeded. The low-

voltage power supply can be powered down while the isolated input is still connected to an active high-voltage

signal or system.

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