Datasheet

LTC2942-1
8
29421f
applicaTions inFormaTion
I
2
C/SMBus Interface
The LTC2942-1 communicates with a bus master using a
2-wire interface compatible with I
2
C and SMBus. The 7-bit
hard-coded I
2
C address of the LTC2942-1 is 1100100.
The LTC2942-1 is a slave-only device. Therefore the serial
clock line (SCL) is an input only while the serial data line
(SDA) is bidirectional. The device supports I
2
C standard
and fast mode. For more details refer to the I
2
C Protocol
section.
Internal Registers
The LTC2942-1 integrates current through a sense resistor,
measures battery voltage and temperature and stores the
results in internal 16-bit registers accessible via I
2
C. High
and low limits can be programmed for each measurement
quantity. The LTC2942-1 continuously monitors these
limits and sets a corresponding flag in its status register
when a limit is exceeded. If the alert mode is enabled, the
AL/CC pin pulls low.
The sixteen internal registers are organized as shown in
Table 1.
Table 1. Register Map
ADDRESS NAME REGISTER DESCRIPTION R/W DEFAULT
00h A Status R See Below
01h B Control R/W 3Ch
02h C Accumulated Charge MSB R/W 7Fh
03h D Accumulated Charge LSB R/W FFh
04h E Charge Threshold High MSB R/W FFh
05h F Charge Threshold High LSB R/W FFh
06h G Charge Threshold Low MSB R/W 00h
07h H Charge Threshold Low LSB R/W 00h
08h I Voltage MSB R XXh
09h J Voltage LSB R XXh
0Ah K Voltage Threshold High R/W FFh
0Bh L Voltage Threshold Low R/W 00h
0Ch M Temperature MSB R XXh
0Dh N Temperature LSB R XXh
0Eh O Temperature Threshold High R/W FFh
0Fh P Temperature Threshold Low R/W 00h
R = Read, W = Write, XX = unknown
Status Register (A)
The status of the charge, voltage and temperature alerts
is reported in the status register shown in Table 2.
Table 2. Status Register A (Read only)
BIT NAME OPERATION DEFAULT
A[7] Chip Identification 0: LTC2942-1
1: LTC2941-1
0
A[6] Reserved Not Used. 0
A[5] Accumulated Charge
Overflow/Underflow
Indicates that the value of the
accumulated charge hit either
top or bottom.
0
A[4] Temperature Alert Indicates one of the
temperature limits was
exceeded.
0
A[3] Charge Alert High Indicates that the accumulated
charge value exceeded the
charge threshold high limit.
0
A[2] Charge Alert Low Indicates that the accumulated
charge value dropped below
the charge threshold low limit.
0
A[1] Voltage Alert Indicates one of the battery
voltage limits was exceeded.
0
A[0] Undervoltage
Lockout Alert
Indicates recovery from
undervoltage. If set to 1, a
UVLO has occurred and the
content of the registers is
uncertain.
X
All status register bits except A[7] are cleared after being
read by the host, if the conditions which set these bits
have been removed.
As soon as one of the three measured quantities exceeds
the programmed limits, the corresponding bit A[4], A[3],
A[2] or A[1] in the status register is set.
Bit A[5] is set if the LTC2942-1’s accumulated charge
registers (ACR) overflows or underflows. In these cases,
the ACR stays at FFFFh or 0000h and does not roll over.
The undervoltage lockout (UVLO) bit of the status register
A[0] is set if, during operation, the voltage on SENSE
+
pin drops below 2.7V without reaching the POR level.
The analog parts of the coulomb counter are switched off
while the digital register values are retained. After recov-
ery of the supply voltage the coulomb counter resumes
integrating with the stored value in the accumulated
charge registers but it has missed any charge flowing
while SENSE
+
< 2.7V.