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AIC1781APSTR Datasheet(PDF) 10 Page - Analog Intergrations Corporation |
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AIC1781APSTR Datasheet(HTML) 10 Page - Analog Intergrations Corporation |
10 / 18 page AIC1781A 10 by the peak voltage timer, which is in turn determined by PEAK pin voltage, the fast charge action is terminated. ∆T/∆t Cutoff The t T/ ∆ ∆ detection of the AIC1781A is performed by sensing the decrease of VTS pin voltage in a specific timer interval dictated by the safety timer. The fast charging terminates when the decrease of VTS pin voltage in 56 seconds exceeds the predetermined value set by ADJ pin input. This time interval of 56 seconds is based on the assumption that voltage of VTS pin is sampled once for every 8 seconds, which is also determined by safety timer. Functioning of - ∆V detection and peak voltage timer (0 V ∆ ) can be disabled if the MODE pin is biased to GND. Functioning of t T/ ∆ ∆ detection can be disabled if the voltage of ADJ pin is higher than VCC - 0.3V. Maximum Safety Timer Cutoff The maximum fast charge period is determined by the safety timer, which is set by a resistor connected from TMR pin to GND. Safety timer, - ∆V sampling rate, and t T/ ∆ ∆ sampling rate will be longer if the resistor value is larger. When the value of the resistor is 100K Ω, the safety timer period equals 80 minutes. This can be verified by biasing MODE pin to VCC and the measured frequency on DSW pin should be around 32.8 KHz. After the safety timer period is finished, the fast charge action is terminated. Maximum Voltage and Temperature Cutoff The AIC1781A guards against the maximum limits for battery voltage and temperature during fast charging. If either of these limits is exceeded, fast charge action is terminated. Trickle Charge There are five different selectable duty cycles for trickle charge after the fast charge to prevent the loss of charge due to battery self-discharging. The duty cycle is controlled by the setting of SEL1 and SEL2 pins. The functions and charging states control mentioned above are illustrated in the function flow chart of AIC1781A (Fig. 16) l DESIGN GUIDE Selecting Peak Voltage Timer (0 ∆V) The voltage of PEAK pin along with safety timer determines the period of peak voltage timer. It can be selected according to the following table: TABLE 1 PEAK PIN PEAK VOLTAGE TIMER VCC 1.5% of safety timer Floating 3.7% of safety timer GND 6% of safety timer Battery Voltage Measurement The AIC1781A measures the battery voltage through VBT pin, which is connected to battery positive terminal through a resistor-divider network, as shown in Fig. 17. The input voltage of SEL3 pin determines the acceptable limit of divided battery voltage. VBAT RA RB C5 2 R5 100K C6 AIC1781A VBT + Fig. 17 Battery Voltage Divider For SEL3 > (VCC/2) + 0.4V, the suggested divider resistance of RA and RB for the corresponding number of battery cells are as below: |
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