ADBMS2950BCCSZ datasheet(19/97 Pages) AD

19 / 97 page

Data Sheet

ADBMS2950B

Rev. 0 | Page 19 of 97

THEORY OF OPERATION

SERIAL INTERFACE OVERVIEW

There are two types of serial ports on the ADBMS2950B: a 2-

wire isolated interface (isoSPI), and a standard, 4-wire SPI. The

state of the ISOMD pin determines whether the pins SDO, SDI,

SCK/IPA, and CSB/IMA form a 2-wire or 4-wire serial port.

Both the 2-wire and 4-wire serial ports can communicate at

2 Mbps. The ADBMS2950B can be used in a daisy-chain

configuration where the second isoSPI interface uses Pins IPB

and IMB. When Port A is configured as a 4-wire interface, Port

A is always the peripheral port, and Port B is the controller

port. Communication is always initiated on Port A of the first

device in the daisy-chain configuration. The final device in the

daisy-chain does not use Port B. For recommendation on the

unused isoSPI port, see the pin descriptions. When Port A is

configured as a 2-wire isoSPI interface, communication can be

initiated at any port allowing any port to become a peripheral or

a controller port.

4-Wire SPI Physical Layer

External Connections

Connecting ISOMD low configures serial Port A for 4-wire SPI.

The SDO pin is an open-drain output that requires a pull-up

resistor connected to the appropriate supply voltage.

Timing

The 4-wire serial port is configured to operate in an SPI system

using either CPHA = 0 and CPOL = 0, or in an SPI system using

CPHA = 1 and CPOL = 1. Consequently, data on SDI must be

stable during the rising edge of SCK. The timing is shown in

Figure 2.

The maximum data rate is 2 Mbps. However, the device is

tested at a higher data rate during production to guarantee

operation at the maximum specified data rate.

2-Wire isoSPI Physical Layer

The 2-wire interface provides a means to interconnect the

ADBMS2950B and ADBMS6830B devices using a simple

twisted pair cabling. Standard SPI signals are encoded in

differential isoSPI pulses as shown in Figure 3 and Figure 4.

The interface is designed for low-packet error rates when the

cabling is subjected to high RF fields. Isolation is achieved

through an external transformer or capacitors.

When using pure capacitive isolation for the isoSPI between the

HV and LV network, it must be considered that voltage

transients across the isolation barrier may cause absolute

maximum voltage or current violation of the IC pins. Such

transients also may disturb the current-sense input pins leading

to false (over) current signals. It is recommended to use a

transformer on the isoSPI link between the HV battery and LV

chassis ground or between multiple reconfigurable (parallel or

series) HV batteries to minimize the capacitance and thus AC

currents between the various subnets. A combination of a

transformer at one end and capacitors at the other end of the

link is also supported. For more details on noise impacting the

(over) current measurement, see the Applications and Current

Sense Inputs sections.

External Connections

The ADBMS2950B has two serial ports: Port A and Port B. Port

B is always configured as a 2-wire interface. Port A is either a 2-

wire or 4-wire interface, which depends on the connection of

the ISOMD pin.

When Port A is configured as a 4-wire interface, then it is

always the peripheral port, and Port B is the controller port.

Communication is always initiated on Port A of the first device

in this daisy-chain configuration. If the final device in the daisy-

chain does not use Port B, it must be terminated or shorted to

the PCB ground plane. Alternatively, the Port B of the last

device can be connected back to a second isoSPI port at the

BMS controller side to implement a communication ring

architecture. This allows a redundant communication path to

all devices in the daisy-chain besides the first that is configured

to a 4-wire interface.

When Port A is configured as a 2-wire interface,

communication can be initiated on either Port A or Port B. If

communication is initiated on Port A, the IC configures Port A

as a peripheral and Port B as a controller. Similarly, if

communication is initiated on Port B, the IC configures Port B

as a peripheral and Port A as a controller. For more details, see

the Reversible isoSPI section.

Reversible isoSPI

Figure 22 shows a daisy-chained configuration of the ADBMS

devices using reversible isoSPI. Two ADBMS6821 or a single

ADBMS6822 is connected to either side of the daisy-chain.

Both ADBMS6821s are configured as controllers and connected

to two separate SPI ports of the BMS controller allowing

simultaneous communication to split daisy-chains

(COMMBK). Alternatively, the ADBMS682x can share the

same SPI to connect to the BMS controller. The BMS controller

then uses two different CS signals to talk to one of the two

channels at a time. The reversible isoSPI provides a redundant

communication path in the event of a single point failure in the

2-wire interface. During normal operation, the COMMBK-

feature allows to split the isoSPI ring to double the

ADBMS2950BCCSZ 数据表(PDF) 19 Page - Analog Devices

ADBMS2950BCCSZ 数据表(HTML) 19 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97

数据表下载