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SAA1501 Datasheet(PDF) 7 Page - NXP Semiconductors |
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SAA1501 Datasheet(HTML) 7 Page - NXP Semiconductors |
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7 / 20 page  December 1994 7 Philips Semiconductors Objective specification Battery charge level indicator SAA1501T Mode detector This block differentiates between the available modes of operation. The modes are given below: Charge mode; power charge (POCH). Discharge mode; battery load (BATLD). Power load mode (POLD); the batteries are charged while the load is also active. Self discharge mode; (STANDBY). To detect power in a regulated system (see Fig.8) the EN signal is used for sensing. The POCH mode is recognized when the converted charge current Ic >Iref2 (when in the power mode, change of mode can only be recognised if EN is HIGH). The BATLD mode is recognized when Id >Iref2; the POLD mode is recognized when Ic >Iref2 and Id >Iref2; the standby mode is recognized when Ic <Iref2 and Id <Iref2. In the standby mode, if the advised frequency (4 kHz) is applied, it takes 0.5 s to determine another mode (in all other modes, a change of mode is sensed continuously). In all other modes an eventual change of mode is done continuously. To save supply current during standby, the V/I converters are switched off. With the specific fixed intervals, the SAA1501T checks whether power or load is connected again. This checking is synchronized by the sensing signal of the V/I converters. The SAA1501T can handle a DC charge current as well as a discontinuous charge current (SMSP charger). The load current can also be DC or interrupted, e.g. produced by a motor. The digital filtering of both signals, to overcome faulty mode detections, restricts the conditions in which power and load are recognized. Because of the very sensitive input detection level of the mode detector for a charge current (power) in combination with the high interference levels of motor driving, the detection level for power (Ic >Iref2) is raised by a factor of 25 when the batteries are loaded. Oscillator As the oscillator has to operate in all modes, including the standby mode, the current consumption of the oscillator must be very low. The same applies for the band gap generator block, because the band gap delivers accurate reference voltages and currents to the oscillator block. Apart from the low current consumption, the accuracy of the period time is important. The period time of the oscillator is: t osc 2C osc × V H V L – () I ref3 --------------------------- 5.6 C osc R ref × × = × = Prescaler/controller In the prescaler, a new system clock is created (CLK) which is used for all timing blocks. Many frequencies are derived from the basic oscillator at the standard frequency of 4 kHz (1/Tosc), such as the self-discharge times and the modulation frequency for the buzzer, the drive voltage frequency for the LCD screen and the pulse trains for temperature measurements and power/load sensing measurements in the mode detector. Temperature In the temperature control block two temperature measurements are performed. In order to switch off fast charging when the battery temperature exceeds an adjustable maximum temperature (Tmax), a maximum temperature measurement is performed. A second temperature measurement is performed in the standby mode. This temperature measurement is input to the temperature control block to switch over the self-discharge rate from a count down of 200 days (based on fosc = 4 kHz) if Tbattery <Tself, to a count down rate of 100 days (based on fosc = 4 kHz) if Tbattery >Tself. In all modes the temperature is measured periodical. The temperature circuit which controls the above mentioned functions is a bridge configuration synthesis, as illustrated in Fig.3. Fig.3 Temperature circuit. |
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