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ADP3806JRUZ-12.5RL Datasheet(PDF) 10 Page - Analog Devices |
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ADP3806JRUZ-12.5RL Datasheet(HTML) 10 Page - Analog Devices |
10 / 16 page REV. B –10– ADP3806 Typical values of RCS range from 25 m W to 50 mW, and the input range of ISET is from 0 V to 4 V. If, for example, a 3 A charger is required, RCS could be set to 40 m W and VISET = 3 V. The power dissipation in RCS should be kept below 500 mW. In this example, the power is a maximum of 360 mW. Once RCS has been chosen, the charge current can be adjusted during operation with VISET. Lowering VISET to 125 mV gives a charge current of 125 mA for trickle charging. Components R3, R4, and C13 provide high frequency filtering for the current sense signal. Final Battery Voltage Control As the battery approaches its final voltage, the ADP3806 switches from CC mode to CV mode. The change is achieved by the common output node of gm1 and gm2. Only one of the two outputs controls the voltage at the COMP pin. Both amplifiers can only pull down on COMP, such that when either amplifier has a positive differential input voltage, its output is not active. For example, when the battery voltage, VBAT, is low, gm2 does not control VCOMP. When the battery voltage reaches the desired final voltage, gm2 takes control of the loop, and the charge cur- rent is reduced. Amplifier gm2 compares the battery voltage to the internal refer- ence voltage of 2.5 V. In the case of the ADP3806-12.5 and ADP3806-12.6, an internal resistor divider sets the selectable final battery voltage. When BATSEL is high, the final battery voltage is set to three cells (12.6 V or 12.525 V). BATSEL can be tied to REG for this state. When BATSEL is tied to ground, VBAT equals four cells (16.8 V or 16.7 V). BATSEL has a 2 mA pull-up current as a fail-safe to select three cells when it is left open. The reference and internal resistor divider are referenced to the AGND pin, which should be connected close to the negative terminal of the battery to minimize sensing errors. In contrast, the ADP3806 requires external, precision resistors. The divider ratio should be set to divide the desired final voltage down to 2.5 V at the BAT pin R R V V BATTERY 11 12 2 5 1 = . – (2) These resistors should have a parallel impedance of approximately 80 k W to minimize bias current errors. When the ADP3806 is in shutdown, an internal switch disconnects the BAT pin as shown in Figure 2. This disconnects the resistor, R11, from the battery and minimizes leakage. The resistance of the internal switch is less than 200 W. VREF SD BATTERY R11 412k 0.1% ADP3806 R12 102k 0.1% BAT BATSEL gm2 Figure 2. Battery Sense Disconnect Circuit Oscillator and PWM The oscillator generates a triangle waveform between 1 V and 2.5 V, which is compared to the voltage at the COMP pin, setting the duty cycle of the driver stage. When VCOMP is below 1 V, the duty cycle is zero. Above 2.5 V, the duty cycle reaches its maximum. MIN OFF TIME BSTREG BST DRVH SW IN DRVL ADP3806 BOOTSTRAPPED SYNCHRONOUS DRIVER CBST PGND 1V 1V Q1 Q2 DELAY DRVLSD SD DELAY CMP3 CMP2 CMP1 + – + – + – Figure 3. Bootstrapped Synchronous Driver |
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