DS2703 SHA-1 Battery Pack Authentication IC

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Table 5. 1-Wire Speed Control Function Commands

COMMAND

HEX

FUNCTION

Clear Overdrive

8D

Clears the Overdrive 1-Wire Speed bit to select Standard 1-Wire

timings

Set Overdrive

8B

Sets the Overdrive 1-Wire Speed bit to select Overdrive 1-Wire

timings

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.

0

200

400

600

800

1000

2.7

3.1

3.53.9

4.34.7

5.15.5

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.

Normal Mode of

Operation Restored

Worst Case Quickest

Transition Time

Worst Case Slowest

Transition

Typical Transition

Time

Valid Thermistor

Measurement Period

DQ Pullup Voltage (V)