DS2703 Dallas Semiconductor, DS2703 Datasheet - Page 9

• Manufacturer Part Number: DS2703
• Description: SHA-1 Battery Pack Authentication IC
• Manufacturer: Dallas Semiconductor

Table 5. 1-Wire Speed Control Function Commands
Clear Overdrive
Set Overdrive
THERMISTOR MEASUREMENT
The DS2703’s 1-Wire interface allows a thermistor to be multiplexed on the DQ line for thermal measurements of
the cell pack without adding an additional pack connection. See the Typical Operating Circuit, Figure 5. The
thermistor is connected between the DQ and THM pins. THM is normally high impedance to prevent the thermistor
from interfering with 1-Wire communication. When an Activate THM command is received, THM is internally driven
to VSS and the DQ pin becomes high impedance allowing the thermistor resistance to be measured. See the
timing diagram in Figure 12.
Figure 2. Thermistor Mode Duration when C
The DS2703 will remain in thermistor measurement mode until the stored charge on the VB pin capacitor is
depleted causing the IC to power cycle back to standard mode of operation. While in thermistor measurement
mode, communication to the DS2703 is not possible. After measuring the thermistor, the host must wait until the
VB capacitor is depleted. Figure 2 shows the typical and worst case transition times over the full operating range
when using .22µF as the VB pin capacitor. Thermistor measurements should be made within the first 100ms after
issuing the command. The host system should then wait until at least 1000ms have passed before sending the next
communication sequence to the IC.
COMMAND
1000
800
600
400
200
0
2.7
Operation Restored
Normal Mode of
3.1
HEX
8D
8B
3.5
Clears the Overdrive 1-Wire Speed bit to select Standard 1-Wire
timings
Sets the Overdrive 1-Wire Speed bit to select Overdrive 1-Wire
timings
DQ Pullup Voltage (V)
3.9
9 of 20
VB
is .22µF
Measurement Period
Valid Thermistor
4.3
FUNCTION
4.7
Worst Case Quickest
Worst Case Slowest
5.1
Transition Time
Typical Transition
Transition
Time
5.5