LTC2943
APPLICATIONS INFORMATION
Alert Response Protocol
SDA pin to see if another device is sending an address at
2
the same time using standard I C bus arbitration. If the
Inasystemwhereseveralslavesshareacommoninterrupt
line, the master can use the alert response address (ARA)
todeterminewhichdeviceinitiatedtheinterrupt(Figure9).
LTC2943 is sending a 1 and reads a 0 on the SDA pin on
the rising edge of SCL, it assumes another device with a
lower address is sending and the LTC2943 immediately
aborts its transfer and waits for the next ARA cycle to try
again. If transfer is successfully completed, the LTC2943
will stop pulling down the ALCC pin and will not respond
to further ARA requests until a new Alert event occurs.
S
ALERT RESPONSE ADDRESS
0001100
R
1
A
0
DEVICE ADDRESS
1100100
A
P
1
2943 F09
Figure 9. LTC2943 Serial Bus SDA Alert Response Protocol
PC Board Layout Suggestions
Keep all traces as short as possible to minimize noise and
inaccuracy. Use a 4-wire Kelvin sense connection for the
sense resistor, locating the LTC2943 close to the resistor
S ADDRESS W A REGISTER A
1100100 02h
S
ADDRESS R A DATA A DATA A
1100100
80h 01h 1
P
0
0
0
1
0
0
2943 F10
+
–
with short sense-traces to the SENSE and SENSE pins.
Use wider traces from the resistor to the battery, load
Figure 10. Reading the LTC2943 Accumulated Charge
Registers (C, D)
+
and/or charger. Put the bypass capacitor close to SENSE
and GND.
S ADDRESS W A REGISTER A DATA P
1100100
0
0
01h
0
4C
TO
R
TO BATTERY
SENSE
CHARGER/LOAD
40ms
8
7
6
5
1
2
3
4
S ADDRESS W A REGISTER A
1100100 08h
S
ADDRESS R A DATA A DATA A
1100100
F1h 80h 1
P
C
0
0
0
1
0
0
LTC2943
2943 F11
Figure 11. ADC Single Conversion Sequence and Reading
of Voltage Registers (I,J)
2943 F12
The master initiates the ARA procedure with a START
conditionandthespecial7-bitARAbusaddress(0001100)
followed by the read bit (R) = 1. If the LTC2943 is as-
serting the ALCC pin in alert mode, it acknowledges and
responds by sending its 7-bit bus address (1100100)
and a 1. While it is sending its address, it monitors the
Figure 12. Kelvin Connection on Sense Resistor
2943fa
17
For more information www.linear.com/LTC2943
Linear [ Linear ]
