DS2438 Dallas Semiconducotr, DS2438 Datasheet - Page 3

• Manufacturer Part Number: DS2438
• Description: Smart Battery Monitor
• Manufacturer: Dallas Semiconducotr

DS2438
PARASITE POWER
The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power
whenever the DQ pin is high. DQ will provide sufficient power as long as the specified timing and
voltage requirements are met (see the section titled “1-Wire Bus System”). The advantage of parasite
power is that the ROM may be read in absence of normal power, i.e., if the battery pack is completely
discharged.
DS2438 BLOCK DIAGRAM Figure 1
OPERATION-MEASURING TEMPERATURE
The DS2438 measures temperatures through the use of an on-board temperature measurement technique.
The temperature reading is provided in a 13-bit, two’s complement format, which provides 0.03125 C of
resolution. Table 1 describes the exact relationship of output data to measured temperature. The data is
transmitted serially over the 1-Wire interface. The DS2438 can measure temperature over the range of
-55 C to +125 C in 0.03125 C increments. For Fahrenheit usage, a lookup table or conversion factor
must be used.
Note that temperature is represented in the DS2438 in terms of a 0.03125 C LSb, yielding the following
13-bit format. The 3 least significant bits of the Temperature Register will always be 0. The remaining
13 bits contain the two’s complement representation of the temperature in C, with the MSb holding the
sign (S) bit. See “Memory Map” section for the Temperature Register address location.
3 of 29