ltc6803g-3 Linear Technology Corporation, ltc6803g-3 Datasheet - Page 12

• Manufacturer Part Number: ltc6803g-3
• Description: Ltc6803-1/ltc6803-3 - Multicell Battery Stack Monitor
• Manufacturer: Linear Technology Corporation

LTC6803-1/LTC6803-3
TIMING DIAGRAM
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
SCKI
CSBI
SDO
SDI
D4
COMMAND
PREVIOUS
t
1
Timing Diagram of the Serial Interface
D3
D3
t
2
t
8
D2
D2
t
4
t
3
D1
D1
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
battery pack. If the V
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
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
+
D0
t
6
D0
pin can be disconnected from the C pins and the
t
5
D7···D4
COMMAND
CURRENT
D7···D4
t
7
680313 TD
+
D3
D3
supply pin is 0V, the LTC6803 will
+
= 0V. See the Applications
680313f