Datasheet

LTC2941-1
8
29411f
applicaTions inFormaTion
I
2
C/SMBus Interface
The LTC2941-1 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 LTC2941-1 is 1100100.
The LTC2941-1 is a slave-only device. Therefore, the serial
clock line (SCL) is input only while the 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 LTC2941-1 integrates current through a sense resistor
and stores a 16-bit result, accumulated charge, as two
bytes in registers C and D. Two byte high and low limits
programmed in registers E, F, G and H are continuously
compared against the accumulated charge. If either limit is
exceeded, a corresponding flag is set in the status register
bits A[2] or A[3]. If the alert mode is enabled, the AL/CC
pin pulls low.
The internal eight 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
R = Read, W = Write
Status Register (A)
Table 2 shows the details of the status register (address
00h):
Table 2. Status Register A (Read Only)
BIT NAME OPERATION DEFAULT
A[7] Chip Identification 1: LTC2941-1
0: LTC2942-1
1
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] Reserved Not used. 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] V
BAT
Alert Indicates that the battery
voltage (at SENSE
–
) dropped
below selected V
BAT
threshold.
0
A[0] Undervoltage
Lockout Alert
Indicates recovery from
undervoltage. If equal to 1,
a UVLO has occurred and
the content of registers is
uncertain.
X
The AL/CC pin can be configured to pull low whenever any
status register bit is set (except for bit A[7] and A[0]), using
control register bits B[2] and B[1]. 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 measured quantities exceeds the
programmed limits, the corresponding bit A[3], A[2] or
A[1] in the status register is set.