4

Application information

4.1

ISO lines circuit - Transformer-Based insulation

The transformer-based insulation is recommended for global communication lines between different modules in a

distributed BMS. It offers better insulation and higher immunity to BCI, being the transformer an intrinsic common

mode filter.

Components Value Unit

Max.

Tolerance

Rating

Comments

60

Ω

10%

1/16 W

Termination resistance. Differential output signal amplitude can be

calculated with the following equation:

VISODIFF=VCOM× RTERM

RDIFF_ISO_OUT

6.8

nF

10%

10 V

Filter common mode noise in the kHz range (inverter and other power

converters). Pole introduced is:

fcut_kℎz=

1

nCCM_KHZ× RISODIFF2+RTERM+7.2kΩ

Do not exceed 10 nF, otherwise common mode settling time upon ISO port

enable will last too long.

22

pF

10%

16 V

Filter common mode noise in the MHz range for improved BCI immunity.

Pole introduced is:

fcut_kℎz= 1

2πCCM_MHZ×RTERM

Do not exceed 47 pF, otherwise differential output signal in high frequency

mode might be strongly distorted.

1

μF

10%

16 V

Deviate energy clamped by DESD directly to GND, preventing any

ESD strike from affecting other PCB components. Total capacity on the

VCOM pin must be equal to 2.2 µF. Hence, in BMS configuration, the

recommended capacity distribution is: 1 µF as CESD_VCOM on the ISOH

clamp, 1 µF as CESD_VCOM on the ISOL clamp, 200 nF as CVCOM

directly on the VCOM pin.

L9963T

Application information

DS13590 - Rev 4

page 32/45