DS1260
OPERATION
During normal operation VCCI (pins 15 and 16) is the primary energy source and power is supplied to
VCCO (pins 12 and 13) through an internal switch at a voltage level of VCCI-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 VCCI falls below the level of 4.25 volts, the power-fail signal is driven low. As VCCI falls
below the level of the lithium supply (VBAT = 3 volts), power is switched and the lithium energy source
supplies power to the uninterruptible output (VCCO) at VBAT-0.2 volts @ 5 mA.
On power-up, as the VCCI supply rises above 3 volts, the primary energy source, VCCI, becomes the
supply. As the VCCI 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 VCCI
.
BATTERY FAIL
When power is being supplied from the primary energy source, BF (Pin 3) is held at a high level (VOH),
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 (VOL), 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 VCCO and BAT
even if VCCI falls below 3 volts. This feature is activated by applying a pulsed input on RST to a high
level (VIH) for 50ns minimum while primary power is valid (see Figure 2). When primary power is
removed after pulsing RST, the VCCO output and BAT will go to high impedance. The next time primary
power is applied such that VCCI is greater than VBAT, normal operation resumes and VCCO will be supplied
by the lithium energy source when VCCI again falls below 3 volts. BAT will also return to the level VBAT
.
Figure 3 shows how the SmartBattery is used in a system application.
BLOCK DIAGRAM Figure 1
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DALLAS [ DALLAS SEMICONDUCTOR ]
