ADBMS2950BCCSZ datasheet(76/97 Pages) AD

76 / 97 page

ADBMS2950B

Data Sheet

Rev. 0 | Page 76 of 97

Figure 58. Surface Mounted Shunt Layout Solder Paste

Wired Shunt Interface

In the case of wire-connected remote shunt applications, an

additional external filter and protection components may be

required, as shown in Figure 59 and Figure 60. Common-mode

chokes with the following common mode capacitors, typical

range 1 nF to 10 nF, adjusted for best filtering performance at

required frequencies, are recommended to be placed.

Optionally, TVS devices can be placed at the shunt connector

pins for increased ESD protection. Small value differential

capacitors can be placed between the current sense pin pairs for

additional high frequency filtering. As short as possible, cables

with twisted sense pairs must be used. The cable length should

not exceed 30 cm in typical applications.

Those measures allow for additional filtering of noise injected

into the wires. Whenever possible, it is recommended to solder

the shunt resistor directly to the PCB with minimum signal

trace length between shunt and IC as shown in the Current

Sense Layout Recommendation section.

Failure modes of components placed in parallel to the shunt or

from any shunt sense pin to GND must be considered. Faults

that alter the shunt resistance may not be detectable at small

currents. The integrated open-wire current sources do not

detect shorts after the filter resistors (shown in Figure 59 left to

the RC filters connect to the IC pins). The I1 vs. I2 comparison

diagnostic does not detect a fault at the I3 inputs that alters the

shunt resistance. It can be detected through the OC3

measurements only above a minimum current level.

To avoid this, a minimum resistance between the shunt and the

additional protection and filtering components can be ensured.

In the failure case, the measured battery current is divided

through the shunt resistance (RSHUNT) and the fault resistance

(RFLT). The current through the fault part can be considered

negligible if it is less than 0.01%, this yields a maximum

tolerable fault resistance of:

RFLT ≥ RSHUNT ÷ 0.01%

Assuming a typical shunt resistance of 50 µΩ the RFLT must be

above 0.5 Ω. Discrete external resistors (REXT) can be added

right in front of the connector pins to ensure this minimum

resistance. To make sure that the additional offset error due to

this resistance together with the current sense pin leakage

currents is below 0.1 µV, the maximum REXT is calculated worst

case according:

REXT ≤ 0.05 µV ÷ (1.5 × 3 nA) ≤ 11 Ω

This assumes IxA and SxA both source 3 nA and IxB sinks

3 nA, or on an average the current through REXT is 1.5 times the

worst-case leakage current. In reality, this is very unexpected to

happen, but as the maximum resistance is well above the

minimum requirement, it provides a comfortable choice of

possible resistor values, for example, standard 3.3 or 4.7 Ω make

a good choice with enough headroom to both limits.

ADBMS2950BCCSZ Arkusz danych(PDF) 76 Page - Analog Devices

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