LTC6803-3 데이터 시트보기 (PDF) - Linear Technology

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LTC6803-3

Multicell Battery Stack Monitor

Linear Technology 

LTC6803-1/LTC6803-3

TIMING DIAGRAM

Timing Diagram of the Serial Interface

SCKI

t1

t2

t4

t3

t6

t7

SDI

D3

D2

D1

D0

D7···D4

D3

t5

CSBI

t8

SDO D4

D3

D2

D1

D0

D7···D4

D3

PREVIOUS

COMMAND

680313 TD

CURRENT

COMMAND

OPERATION

THEORY OF OPERATION

The LTC6803 is a data acquisition IC capable of mea-

suring the voltage of 12 series connected battery cells.

An input multiplexer connects the batteries to a 12-bit

delta-sigma analog-to-digital converter (ADC). An internal

8ppm/°C voltage reference combined with the ADC give

the LTC6803 its outstanding measurement accuracy. The

inherent benefits of the delta-sigma ADC versus other types

of ADCs (e.g., successive approximation) are explained

in Advantages of Delta-Sigma ADCs in the Applications

Information section.

Communication between the LTC6803 and a host processor

is handled by an SPI compatible serial interface. As shown

in Figure 1, the LTC6803-1s or LTC6803-3s can pass data

up and down a stack of devices using simple diodes for

isolation. This operation is described in Serial Port in the

Applications Information section.

The LTC6803 also contains circuitry to balance cell voltages.

Internal MOSFETs can be used to discharge cells. These

internal MOSFETs can also be used to control external

balancing circuits. Figure 1 illustrates cell balancing by

internal discharge. Figure 12 shows the S pin controlling

an external balancing circuit. It is important to note that

the LTC6803 makes no decisions about turning on/off

the internal MOSFETs. This is completely controlled by

the host processor. The host processor writes values to

12

a configuration register inside the LTC6803 to control the

switches. The watchdog timer inside the LTC6803 will turn

off the discharge switches if communication with the host

processor is interrupted.

The LTC6803 has three modes of operation: hardware

shutdown, standby and measure. Hardware shutdown is

a true zero power mode. Standby mode is a power saving

state where all circuits except the serial interface are turned

off. In measure mode, the LTC6803 is used to measure

cell voltages and store the results in memory. Measure

mode will also monitor each cell voltage for overvoltage

(OV) and undervoltage (UV) conditions.

HARDWARE SHUTDOWN MODE

The V+ pin can be disconnected from the C pins and the

battery pack. If the V+ supply pin is 0V, the LTC6803 will

typically draw less than 1nA from the battery cells. All

circuits inside the IC are off. It is not possible to com-

municate with the IC when V+ = 0V. See the Applications

Information section for hardware shutdown circuits.

STANDBY MODE

The LTC6803 defaults (powers up) to standby mode.

Standby mode is the lowest supply current state with

a supply connected. Standby current is typically 12µA

680313f

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