LT8584
16
8584fb
For more information www.linear.com/LT8584
operaTion
Serial Timer Decode Window
The timer initiates on the first negative edge on the D
IN
pin.
RTMR pin remains high for the duration of the timer which
signifies the decode window for the serial input counter.
A resistor from the RTMR pin to ground sets the decode
window duration. The duration can be accurately set from
1.9ms (R
RTMR
= 10k) to 31ms (R
RTMR
= 200k). The timer
can be set outside this range, but the accuracy decreases.
The serial input counter stops counting and latches the
data once the RTMR pin goes low; after which, the OUT
pin amplifier input MUX selects the desired measurement,
and the discharger is set to the right state.
Serial Communication Fault Modes
The serial interface has several fault monitors that prevent
entering undesired modes due to a communication error.
The OUT pin is set to V
VIN
– 1.4V to indicate the LT8584 is
in fault. The part remains in fault from the onset of RTMR
going high until the first count is detected. If no count is
seen by the serial input counter during the decode window,
the fault is latched. If the serial input counter counts higher
than 4 negative edges, the fault latch is
set.
A
third latching fault occurs if an internal undervoltage
lockout (UVLO) is detected during the decode window.
This protects against undesired operation if data latches
or the serial input counter were reset. The part must be
reset by taking D
IN
high to clear a fault.
D
IN
Pin and Serial Bus Timing
Several internal passive filters are added to the data bus
to prevent injected system noise corrupting serial com
-
munication. These filters have time constants that place
constraints on the serial communication timing require-
ments (see the
Timing Diagram). The LT8584 can reject
up to 4µs of erroneous glitches on the D
IN
pin in either
direction. The power latch filter can also reject up to a
4µs glitch on D
IN
.
The D
IN
pin has built-in hysteresis of approximately 100mV.
This allows the serial input counter to recognize both slow
and fast edges without erroneous behavior. The discharger
activation or deactivation time is typically less than 3µs
and is a direct indication of the switch enable latch state.
OUT Pin Analog MUX
An internal multiplexer, MUX, selects between V
CELL
and
the OUT pin amplifier based on one of the selected Serial
Modes shown in Table 1. The
OUT pin amplifier has a
5kΩ
internal load and has several inputs including: V
TEMP
,
the 19•V
SNS
amplifier, and six handshake voltages. The
internal MUX defaults to V
CELL
in shutdown—consuming
no power in the process—and provides a 55Ω nominal
resistance from the V
CELL
pin to the OUT pin. Figure 6
shows the connection of the OUT pin to a BSM and its
internal analog MUX.
The MUX switches over to one of the handshake voltage
levels once both the LT8584 and the decode window are
activated. The OUT amplifier will indicate a fault at start-up
until the serial input counter recognizes the first negative
edge on D
IN
. Subsequent negative edges on D
IN
cause the
MUX to select the handshake voltage corresponding to the
number of edges counted. These voltage levels provide a
means of verifying if the serial interface has recognized
the correct count. Note that the OUT pin amplifier has an
approximate 200µs one percent settling time when driving
a 220nF load capacitance.
Once the RTMR pin goes low, the MUX selects the OUT pin
mode corresponding to the number of serial input counts
(see Table 1 for available modes). The part can also
be
placed in shutdown when RTMR is low and the decode
window has expired.
V
CELL
Measurement
The user can measure the cell voltage by measuring
the voltage on the OUT pin either with the part disabled
(discharger off) or with the part enabled in MODE 1 (dis
-
charger on), see Table 1. The LT8584 uses an internal
PMOS switch with R
DSON
= 55Ω to connect V
CELL
to the
OUT pin. Note that any current flowing into or out of the
OUT pin will cause a measurement error due to the IR
drop across the switch.
V
SNS
19× Amplifier
An amplifier is provided to allow the user to monitor the
discharger current. This measurement can only be per
-
formed when the discharger is on (MODE 2). The differ-
ential voltage
between V
VCELL
and V
VSNS
is amplified 19×.
