LT8584
15
8584fb
For more information www.linear.com/LT8584
operaTion
SERIAL MODE OPERATION
Use serial mode if monitoring the discharging current
and/or the die temperature are required. Connecting the
MODE pin to GND enables serial communication. The D
IN
pin is used to input serial data through a custom serial
bus (see Figures 4 and 5).
Serial Mode Safety Features
The LT8584 provides the user with several levels of safety
and verification. The LT8584 has built in switch protec
-
tion that detects and halts power delivery during either
a primary-side open or short, a secondary-side open or
short, or an overvoltage on the primary or secondary. The
LT8584 outputs the V
SW,ERR
handshake that can be read
back by the battery stack monitor (BSM).
The LT8584 also detects communication errors including
too many or too few D
IN
pulses or a UVLO condition. The
LT8584 outputs the V
FAULT
handshake that can be read
back by the BSM.
The LT8584 also provides critical cell parameters including
temperature, discharge current, cell voltage, and cell and
connection DC resistance. These are all read back by the
BSM. As the cell starts to age, the cell impedance increases.
This allows the user to perform preventative maintenance,
keeping the system down time
to a minimum.
Finally,
the LT8584 handshake voltages are ±3% accurate
independent references that can be used to verify that every
channel in the BSM is measuring accurately.
Serial Architecture
Power to the part is latched on the first negative edge
of D
IN
signal and remains latched for the duration of the
decode window, t
W
. This allows the D
IN
pin to be toggled
for communicating serial data without resetting the part.
The LT8584 counts the number of negative edges seen
on the D
IN
pin. Note that the first edge, which initiates se-
rial communication
and latches the part, is not counted.
There are four active modes the user can select as shown
in Table 1. Handshaking is accomplished by reading the
analog voltage on the OUT pin. Handshaking voltages
are asserted on the negative edge of the D
IN
signal, cor-
responding to the serial decode count.
Once
the decode window expires and RTMR pin returns
to ground, three actions are initiated: the OUT pin analog
multiplexer switches to the desired measurement, the dis
-
charger turns
on depending on selected mode in Table 1,
and the input power latch disables. Note that the LT8584
can
only be disabled after the decode window has expired
and the D
IN
pin has been taken high.
Table 1.Serial Mode States
PULSE
COUNT MODE
DISCHARGER
ST
ATE
MUX
OUTPUT
HANDSHAKE
VOLTAGE
(V
VIN
– V
OUT
)
Part Disabled 0 Disabled V
CELL
N/A
0 Fault Disabled V
FAULT
1.4
1 1 Enabled V
CELL
0.2
2 2 Enabled V
SNS
0.4
3 3 Enabled V
TEMP
0.6
4 4 Disabled V
TEMP
0.8
≥5 Fault Disabled V
FAULT
1.4
Figure 5. Serial Communication Architecture
8584 F05
2-BIT
RIPPLE
COUNTER
Y0
Y1
POR
RST
Q
Q
S
R
MODE 1
MODE 2
MODE 3
MODE 4
POR
Q
Q
S
R
1-SHOT
11-BIT
RIPPLE
COUNTER
OSCILLATOR
EN
POR
V
DD
POR
DIN
Y0
Y11RST
V
DD
A
B
C
D
2 × 4
DECODER
a
b
