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DS2788 Datasheet(PDF) 7 Page - Maxim Integrated Products |
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DS2788 Datasheet(HTML) 7 Page - Maxim Integrated Products |
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7 / 32 page  nection or system shutdown, in which no charge or dis- charge current flows. A PMOD SLEEP condition transi- tions back to ACTIVE mode when DQ is pulled high. The second option for entering SLEEP is an undervolt- age condition. When the UVEN bit is set, the DS2788 transitions to SLEEP if the voltage on VIN is less than VSLEEP (2.45V nominal) and DQ is stable at a low or high logic level for tSLEEP. An undervoltage condition occurs when a pack is fully discharged, where loading on the battery should be minimized. UVEN SLEEP relieves the battery of the IACTIVE load until communi- cation on DQ resumes. Note: PMOD and UVEN SLEEP features must be dis- abled when a battery is charged on an external charger that does not connect to the DQ pin. PMOD SLEEP can be used if the charger pulls DQ high. UVEN SLEEP can be used if the charger toggles DQ. The DS2788 remains in SLEEP and therefore does not measure or accumulate current when a battery is charged on a charger that fails to properly drive DQ. Initiating Communication in Sleep When beginning communication with a DS2788 in PMOD SLEEP, DQ must be pulled up first and then a 1-Wire reset pulse must be issued by the master. In UVEN SLEEP, the procedure depends on the state of DQ when UVEN SLEEP was entered. If DQ was low, DQ must be pulled up and then a 1-Wire reset pulse must be issued by the master as with PMOD SLEEP. If DQ was high when UVEN SLEEP was entered, then the DS2788 is prepared to receive a 1-Wire reset from the master. In the first two cases with DQ low during SLEEP, the DS2788 does not respond to the first rising edge of DQ with a presence pulse. Voltage Measurement Battery voltage is measured at the VIN input with respect to VSS over a range of 0 to 4.5V, with a resolu- tion of 4.88mV. The result is updated every 440ms and placed in the Voltage (VOLT) register in two’s comple- ment form. Voltages above the maximum register value are reported at the maximum value; voltages below the minimum register value are reported at the minimum value. Figure 3 shows the format of the Voltage register. VIN is usually connected to the positive terminal of a single-cell Li+ battery by a 1k Ω resistor. The input impedance is sufficiently large (15M Ω) to be connected to a high-impedance voltage-divider in order to support multiple-cell applications. The pack voltage should be divided by the number of series cells to present a sin- gle-cell average voltage to the VIN input. In Figure 2, the value of R can be up to 1M Ω without incurring sig- nificant error due to input loading. The VMA pin is dri- ven high tPRE before the voltage conversion begins. This allows an external switching element to enable the voltage-divider, and allows settling to occur before the start of the conversion. Stand-Alone Fuel-Gauge IC with LED Display Drivers _______________________________________________________________________________________ 7 VOLT READ ONLY MSB—ADDRESS 0Ch LSB—ADDRESS 0Dh S 29 28 27 26 25 24 23 22 21 20 X X X X X MSb LSb MSb LSb “S”: SIGN BIT(S), “X”: RESERVED UNITS: 4.88mV Figure 3. Voltage Register Format |
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