Datasheet LTC1980 (Analog Devices) - 10

LTC1980
U OPERATIO Lithium-Ion Battery Charger Operation
will maintain the programmed preset float voltage across the battery until the timer terminates the charge cycle. With the wall adapter power applied, the LTC1980 oper- During trickle charging, if the battery voltage remains ates as a constant-current/constant-voltage PWM battery below 2.7V for 1/4 of the total programmed charge time, charger, with a portion of the adapter current used for the battery may be defective and the charge cycle ends. charging and the rest flowing to the system load through Also, if a battery open circuit is detected, the charge cycle an optional low dropout regulator. ends immediately. The charger can be shut down by A charge cycle begins when the voltage at VREG exceeds pulling the REG pin low, although the timer will continue the undervoltage lockout threshold level and the IC is until it times out. enabled via the MODE pin. If the battery has been deeply discharged and the battery voltage is less than 2.7V, the
Power Converter Operation from Battery
charger will begin with the programmed trickle charge When the AC adapter is removed, the LTC1980 operates as current. a DC/DC PWM converter using the battery for input power When the battery exceeds 2.7V, the charger begins the to provide a regulated output voltage for the system load. constant-current portion of the charge cycle with the The LTC1980 is a current mode switcher. This means that charge current equal to the programmed level. As the the switch duty cycle is directly controlled by switch battery accepts charge, the voltage increases. When the current rather than by output voltage or current. Battery battery voltage reaches the recharge threshold, the pro- charger operation will be described for the simplified grammable timer begins. Constant-current charging con- diagram (Figure 3). At the start of the oscillator cycle, latch tinues until the battery approaches the programmed charge U9 is set causing M2 to turn on. When switch current voltage of 4.1V or 4.2V/cell at which time the charge reaches a predetermined level M2 turns off and M1 turns current will begin to drop, signaling the beginning of the on. This level is set by the control voltage at the output of constant-voltage portion of the charge cycle. The charger error amplifier U10. U1 VOLTAGE SELECTION VBAT V T1 REG WALL + C2 ADAPTER B1 C1 SN1 SNUBBER SN2 SNUBBER R1 NETWORK NETWORK – U2 TO SYSTEM R2 BDRIVE RDRIVE LOAD U4 M1 M2 + + – R12 C6 DRIVERS DIRECTION SENSE V V REF REF R13 TYPICAL CURRENT U7 WAVEFORM AMPLIFIER – R5 OSC S + U9 Q + + R U5 R4 U6 U8 + – – – ZC R6 PWM SW1 C3 R7 R9 R8 – C4 SW2 SW3 U10 R10 + – EA U12 R11 + U11 C5 VREF REFERENCE 1980 F03
Figure 3. Simplified Diagram—Power Converter
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