LTC6802IG-2 LINER [Linear Technology], LTC6802IG-2 Datasheet - Page 13

• Manufacturer Part Number: LTC6802IG-2
• Description: Multicell Addressable Battery Stack Monitor
• Manufacturer: LINER [Linear Technology]

operaTion
DISCHARGING DURING CELL MEASUREMENTS
The primary cell voltage A/D measurement commands
(STCVAD and STOWAD) automatically turn off a cell’s
discharge switch while its voltage is being measured. The
discharge switches for the cell above and the cell below will
also be turned off during the measurement. For example,
discharge switches S4, S5, and S6 will be disabled while
cell 5 is being measured.
In some systems it may be desirable to allow discharging
to continue during cell voltage measurements. The cell
voltage A/D conversion commands STCVDC and STOWDC
allow any enabled discharge switches to remain on during
cell voltage measurements. This feature allows the system
to perform a self test to verify the discharge functionality
and multiplexer operation.
All discharge switches are automatically disabled during
OV and UV comparison measurements.
A/D CONVERTER DIGITAL SELF TEST
Two self-test commands can be used to verify the func-
tionality of the digital portions of the ADC. The self tests
also verify the cell voltage registers and cell temperature
registers. During these self tests a test signal is applied
to the ADC. If the circuitry is working properly the cell
voltage or cell temperature registers will contain identi-
cal codes. For self test 1 the registers will contain 0x555.
For self test 2, the registers will contain 0xAAA. The time
required for the self-test function is the same as required
to measure all cell voltages or all temperature sensors.
Perform the self-test function with CDC[2:0] set to 1 in
the configuration register.
USING THE S PINS AS DIGITAL OUTPUTS OR
GATE DRIVERS
The S outputs include an internal 10k pull-up resistor.
Therefore the S pins will behave as a digital output when
loaded with a high impedance, e.g., the gate of an external
MOSFET. For applications requiring high battery discharge
currents, connect a discrete PMOS switch device and suit-
able discharge resistor to the cell, and the gate terminal
to the S output pin, as illustrated in Figure 4.
POWER DISSIPATION AND THERMAL SHUTDOWN
The MOSFETs connected to the Pins S1 through S12 can be
used to discharge battery cells. An external resistor should
be used to limit the power dissipated by the MOSFETs. The
maximum power dissipation in the MOSFETs is limited by
the amount of heat that can be tolerated by the LTC6802-2.
Excessive heat results in elevated die temperatures. The
electrical characteristics are guaranteed for die tempera-
tures up to 85°C. Little or no degradation will be observed
in the measurement accuracy for die temperatures up
to 105°C. Damage may occur near 150°C, therefore the
recommended maximum die temperature is 125°C.
To protect the LTC6802-2 from damage due to overheating,
a thermal shutdown circuit is included. Overheating of the
device can occur when dissipating significant power in the
cell discharge switches. The problem is exacerbated when
operating with a large voltage between V
the thermal conductivity of the system is poor.
If the temperature detected on the device goes above ap-
proximately 145°C, the configuration registers will be reset
to default states, turning off all discharge switches and
disabling A/D conversions. When a thermal shutdown has
occurred, the THSD bit in the temperature register group
will go high. The bit is cleared by performing a read of the
temperature registers (RDTMP command).
Since thermal shutdown interrupts normal operation, the
internal temperature monitor should be used to determine
when the device temperature is approaching unacceptable
levels.
Figure 4. External Discharge FET Connection (One Cell Shown)
+
15
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VISHAY CRCW2512 SERIES
SI2351DS
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LTC6802-2
68022 F04
+
and V
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–
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