Real-time clock ds1302 used in combination with super capacitor/Farah Capacitor

Http://blog.sina.com.cn/s/blog_630630870100l340.html

Abstract: This paper introduces the working principle of high-precision analog-to-digital converter ad7671, and describes the implementation method of high-speed and high-precision data collection based on ad7671 and TMS320VC5402, the circuit diagram of the hardware circuit and the corresponding debugging program are provided.
Keywords: Ad7671; high precision; DSP; data collection

Dallas semiconductor ds1302 streaming charging clock chip is a programmable 3-line serial interface clock chip that can be used to back up the system time and date with super capacitors or rechargeable battery, it also provides 31-byte non-easy-to-lose SRAM for data storage. By
As shown in power backup circuit 1 composed of ds1302 and super capacitor, ds1302 vcc2 is connected to the main power supply, and vcc1. For different power backup systems, such as rechargeable Ni-MH batteries, nickel-cadmium batteries, and super capacitors with different capacities, ds1302 provides a programmable fl stream charging circuit, to adapt to different charging current requirements, the charging circuit 2 shows.
You can set different maximum charge current IMAX by setting the DS and RS control bit in the circuit. For example, if the control word is 10100101, it indicates that a diode is selected, and R1 with 2 k Ω is selected. The IMAX formula is shown in Formula 1, the vdrop is the voltage drop of the diode.

IMAX = (VCC2-n · vdrop)/R n = 1, 2 (1)
Table 1 lists the IMAX computing values. The corresponding values of vcc2 are 4.5 V, 5.0 V, and 5.5 V. There are one diode and two diodes, the resistance values are 2 K, 42 k, and 82k.

Charging Process

As a power backup component, the charge and discharge characteristics of super capacitors are the focus of attention. Combined with the programmable charging circuit of ds1302, the voltage V (t) during charging is given below) and the function of current I (T) and time, and the function of voltage V (T) and time during discharge.
The function of super capacitor terminal voltage and time can be expressed as type 2.
V (t) = vmax [1-e (-T/RC)] (2)
V (t) is the super capacitor end voltage, Vmax is equal to vcc2 minus N · vdrop, r is the internal streaming charging resistance, and C is the capacity of the super capacitor. The time required to charge the voltage at both ends of the super capacitor to 95% of the Vmax is shown in table 2.
The charge current and time functions can be expressed as type 3.
I (t) = vmax/R · E (-T/RC) (3)
I (t) is the charging current.
Supercapacitor charging characteristic curve 3 is shown.

Discharge Process
To know the time when ds1302 uses a super capacitor for discharge, You Need To Know ds1302's characteristic parameter icc1t (time-preserving current). icc1t changes linearly, which means ds1302 can be expressed as a resistive load RL, the supercapacitor uses this load to discharge. According to the ds1302 Data Manual, icc1t is 0.3 μA when vcc1. in this way, rl is about 8.3m Ω. The discharge characteristics of a super capacitor can be expressed as type 4 without considering the effect of the self-discharge of the super capacitor.
V (t) = vmax · E (-T/RLC) (4)
RL is the load impedance of ds1302. The discharge time calculated based on the above formula is shown in table 3.
See Figure 4.
This article introduces an application example of real-time clock ds1302 and super capacitor, which helps the designer to design circuits such as clock persistence and data persistence using super capacitor.

Enterprise information

 

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High-tech enterprises specializing in the production of super capacitors in China. The main R & D personnel began to undertake the Ministry of Science and Technology from the 15th Five-Year Plan Period863 plan the electric vehicle major special "electric vehicle super capacitor" project. After years of research and experimentation on key national projects, combined with the actual needs of domestic and foreign markets,The product is now available in 2.5 V/2.7v series for production, 5.0 V/5.5v series for combination, 5 V series for stacked sheets, and 10 V, 20 V, 50 V, 100 V, 200 V for large capacity, 300 V, V series Farah capacitor modules, module series products, etc.. The performance indicators of over one hundred super capacitors have reached the same level at home and abroad.

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