DS1260 Datasheet, PDF (2/8 Pages) Dallas Semiconductor – Smart Battery

DS1260
OPERATION
During normal operation V_CCI (pins 15 and 16) is the primary energy source and power is supplied to
V_CCO (pins 12 and 13) through an internal switch at a voltage level of V_CCI-0.2 volts @ 250 mA. During
this time the power-fail signal ( PF ) is held high, indicating valid primary voltage (see Figure 1).
However, if the V_CCI falls below the level of 4.25 volts, the power-fail signal is driven low. As V_CCI falls
below the level of the lithium supply (V_BAT = 3 volts), power is switched and the lithium energy source
supplies power to the uninterruptible output (V_CCO) at V_BAT-0.2 volts @ 5 mA.
On power-up, as the V_CCI supply rises above 3 volts, the primary energy source, V_CCI, becomes the
supply. As the V_CCI input rises above 4.25 volts, the power-fail signal is driven back to the high level.
During normal operation, BAT (Pin 5) stays at the battery level of 3 volts, regardless of the level of V_CCI.
BATTERY FAIL
When power is being supplied from the primary energy source, BF (Pin 3) is held at a high level (V_OH),
provided that the lithium energy source is greater than 2 volts. If the lithium energy source should
decrease to below 2 volts, the BF signal is driven low (V_OL), indicating an exhausted lithium battery. The
BF signal is always low when power is being supplied by the lithium energy source.
RESET
The reset input can be used to prevent the lithium energy source from supplying power to V_CCO and BAT
even if V_CCI falls below 3 volts. This feature is activated by applying a pulsed input on RST to a high
level (V_IH) for 50ns minimum while primary power is valid (see Figure 2). When primary power is
removed after pulsing RST, the V_CCO output and BAT will go to high impedance. The next time primary
power is applied such that V_CCI is greater than V_BAT, normal operation resumes and V_CCO will be supplied
by the lithium energy source when V_CCI again falls below 3 volts. BAT will also return to the level V_BAT.
Figure 3 shows how the SmartBattery is used in a system application.
BLOCK DIAGRAM Figure 1
2 of 8