Datasheet

LTC2942
8
2942fa
operaTion
Power-Up Sequence
When SENSE
+
rises above a threshold of approximately
2.5V, the LTC2942 generates an internal power-on reset
(POR) signal and sets all registers to their default state.
In the default state, the coulomb counter is active while
the voltage and temperature ADC is switched off. The
accumulated charge register is set to mid-scale (7FFFh),
all low threshold registers are set to 0000h and all high
threshold registers are set to FFFFh. The alert mode is
enabled and the coulomb counter prescaling factor M is
set to 128.
applicaTions inFormaTion
I
2
C/SMBus Interface
The LTC2942 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 is 1100100.
The LTC2942 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 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 continuously monitors these limits
and sets a flag in the onboard 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