DS2770

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SECONDARY CHARGE TERMINATION

Two secondary charge terminations are included. Independent of battery technology selection, charge

terminates if the maximum charge temperature is exceeded or the charge timer expires. The CSTAT1 and

CSTAT0 bits in the Status Register will both be set to 1 to indicate a “charge sequence completed” status.

The maximum charge time is set in the Charge Time Register, CTR. CTR is initialized from lockable

EEPROM location address 34h at the start of fast charge ( CC driven low after initiation). CTR

terminated. Since CTR is writable, the value in CTR may be overwritten at any time during a charge to

modify the maximum charge time. Figure 4 shows the format of CTR.

CHARGE TIME REGISTER Figure 4

Address 06

MSb

LSb

Units: 0.015625h

CURRENT MEASUREMENT

In the Active Mode of operation, the DS2770 continually measures the current flow into and out of the

battery by measuring the voltage drop across a current-sense resistor. The DS2770 is available in two

configurations: 1) internal 25m

W current-sense resistor; 2) external user-selectable sense resistor. In

battery (discharging). Note that when an external sense resistor is used, one end of the resistor must be

wired directly to VSS (the negative terminal of the cell) for proper operation of the current measurement

circuitry.

two’s complement format every 3.52 seconds. The Current Register value represents the average current

over 3.52 seconds. Currents outside the register’s range are reported at the limit of the range. Figure 5

shows the format of the Current Register.

For the internal sense resistor configuration, the DS2770 maintains the Current Register in units of amps,

with a resolution of 62.5

mA and a full-scale range of ±2.048A. The DS2770 automatically compensates

for internal sense resistor process variations and temperature effects when reporting current.

Register, with a resolution of 1.56

mV and a full-scale range of ±51.2mV.