DS202 is designed with a built-in lithium cell for convenient measurement. This guide serves to analyze the power management and the batter-charging process. 1. Main Networks of Power Supply This section chiefly describes the main networks of power supply of the PCB on DS202. 1.1 3V6 This network voltage is the same as that of the battery, which has proven to be true in the measurement result. The LCD backlight chip, the buzzer and the power management integrated circuits－AXP192 are all within this voltage range. 1.2 3V This voltage is exported from the first road-DCDC of the power management ICs AXP192. The measured voltage is approximately 3V (adjustable vie software). It supplies power to the LCD Module, the MCU, the FLASH, etc. 1.3 +V This voltage is exported from the third road-LDO of the power management ICs AXP192. The measured voltage is 3V (adjustable vie software). It provides the positive power rail for the operational amplifier-OPA2354, and the analog switches-HC4053. 1.4 -V This voltage comes from the conversion of 3V power supply system through the charge pump-TPS60403. The measured voltage is -3V. The voltage amplitude is subject to the input voltage. It provides the negative power rail for the operational amplifier-OPA2354, and the analog switches-HC4053. 1.5 Vm This is connected to 3V power supply network vie a 100uH inductor. It supplies power to the touch control chip-HC640. 2. Power Management Integrated Circuits 2.1 AXP192 AXP192 is responsible for managing the charging and discharging of the lithium cell. The 3 road step-down converter serves to regulate the output of DCDC, and the 4 line voltage stabilizer serves to regulate the output of LDO. The integrated circuits manage various kinds of power and control the circuit for the MCU port. The following passages excepted from the AXP192 Data Manual analyze the charging based on AXP192. AXP192 incorporates highly integrated circuits for power management. It is specifically designed for application of the single-cell lithium battery (lithium-ion or lithium-polymer) that needs multiplex power output through conversion. It offers a simple and flexible solution to power distribution. It fully meets the demand for relatively complex and precise control of power from increasingly complicated CPUs. AXP192 includes a built-in USB compatible battery charger, a three road step-down converter(Buck DC-DV converter), a four line voltage stabilizer(LDO), voltage/electric current/temperature monitoring multiplex 12-Bit ADC. To ensure the security and stability of the power system, AXP192 also integrates over voltage protection(OVP), under voltage protection(UVP), over temperature protection(OTP) and over current protection(OCP) to protect the circuit. AXP192 contains the Intelligent Power Select (IPS TM) that serves to safely and clearly distribute power between the USB, the external AC adaptor, the lithium battery and the application system load, and also helps to keep the application system working as usual with an external source of power even when the battery is absent, over-discharged or damaged. AXP192 can be powered by an external source of power such as an adaptor, a USB, and a battery. It supports a chargeable backup battery. AXP192 is equipped with a Two Wire Serial Interface(TWSI) that communicates with the host system. Through this TWSI, the application possessor can open or shut some power outputs, set their voltage, access the internal register and various sorts of measurement data including Fuel Gauge. The measurement data of the high-precision(0.5%) electric quantity offers a distinct picture of real-time consumption of power for the consumers. 2.2 TPS60403 TI’s charge pump chip features an input voltage range from 1.6V to 5.5V, an output voltage range from -1.6V to -5.5V, and a maximum load of 60mA. In a DS202, it serves to convert 3V power into -3V power to provide the negative power rail for the analog amplifier and the analog switches. 2.3 QX5239B It serves to provide backlighting to the LED module. MCU can adjust the intensity of the LCD backlight by regulating the 2-foot input signal duty cycle. The measured PWM pulse frequency is 360Hz. 2.4 Lithium Polymer Battery The nominal capacity is 500mAh. The nominal voltage is 3.7V. The cutoff voltage for charging is 4.2V. The measured end-of-charging voltage displays 4.12V. It seems its capacity is yet to be optimum. This battery could be replaced with one with a larger capacity. The next section will measure its capacity. 3. The charging test Preparations for the charging (see pic 1): HP 5V2A (charger), UIMerter5.08 (terminal interface input), common USB port output, UIMM software (recoding data to the CSV table)
Pic 1 DS202 Charging
The analysis in this section is based on the data above. You may download the data to run a DIY test. Before the charging started, DS202 had automatically shut itself down. As is tested, it will power off itself when the voltage of the lithium battery reaches below 3V. 2015/02/05 21:21:10 Charging starts. Initial electric current value shows 446.0mA. Constant-current charging begins. 2015/02/05 22:19:16 Move onto the phase of float charging. Charging current starts to experience a steady decline. . 2015/02/05 22:53:27 Float charging ends with a charging current value at 0. Before it ended, the current value registered 51.5mA. In other words, it cut off at 0.1C. The phase of float charging cost 34 minutes. The entire charging process covered 1h32m. The charged electric quantity was 0.5194Ah, 2.6910Wh. The average voltage was 5.1810V. When the charging was finished, the input electric current of DS202 was 0. The change of voltage and current during the charge is displayed in Pic2. As is shown in the graph, throughout the charging, voltage remained steady. During the constant-current charging phase, the electric current stayed almost unchanged. During the float charging phase, the current experienced a smooth decline. The float charging phase saw a perfect curve. The current cut off at a standard value of 0.1C. On the whole, both the voltage and the current displayed a perfect curve.
Pic 2 Voltage Curve and Current Curve The graph below shows the curve of electric quantity separately in Ah and in Wh during the charging process. In the phase of constant-current charging, the electric quantity rose linearly. When it came to the float charging process, the gradient started to decline. The growth of electric current became modest. When the charging process ended, the gradient became 0. The electric current stopped growing.  Pic 3 Electric Quantity Curve
The graph below presents the environmental temperature during the charge. As can be seen from the graph, the environmental temperature varied from a low of 23.6℃ to a high of 24.6℃, indicating an average of 24.3℃. Pic 4 Environmental Temperature Curve
Table 1 gives an overview of the data in this test.
Table 1 DS202 Charge Test Data Device Mode | MiniDSO-DS202 | Remarks | Battery Specification | 500mAh 3.7V |
| Platform | AXP192 |
| Charge Methods | Constant current and constant voltage |
| Constant-current Charging Time Length | 58minutes |
| Constant-current Average Electric Current | 434.2mA |
| Float Charging Time Length | 51.5mA | 0.1C | Total Time for Charging | 1hour 32minutes |
| Charged Electric Quantity Ah | 0.5194Ah |
| Charged Electric Quantity Wh | 2.6919Wh |
|
AXP192 exhibited excellent quality during the charging process. The process displayed standard constant-current and constant-voltage charging with a perfect electric current curve in which the charging current cut off at 0.1C, followed by a 0 input of electric current.
DS202 standard configuration features a 500mAh lithium battery. 519.4mAh was charged into it in this test. Presumably, the AXP192 charge is characterized by a linear course under the power-off condition. Therefore the input current from the USB port equaled the input current to the battery. It could be deduced that the actual capacity of the battery is approximately 519.4mAh, which is completely sufficient.
The entire charging process took 1 hour and 32 minutes. The maximum electric current was below 45mA. The standard USB port sufficed to supply a minimum current of 500mA. Therefore, the power supply would not be a concern in the use of DS202. The USB port was a MircroUSB port employed by a vast majority of cellphones. One single-cell 18650 mobile power bank sufficed to fully charge DS202 up to three times. If usually you can hardly access the commercial power, you may use an Mi 16000mAh mobile power bank which is available for over 20 times full charging.
1. Conclusion and Suggestion DS202 features an AXP192 power management integrated circuits with excellence in charging, and a built-in 500mAh lithium polymer battery with a rich capacity. The battery charge(roughly 1C) only takes one and a half hour, which is shorter than that needed by most cellphones on the market. The cutoff electric current demonstrates precision.
A significant piece of advice is: Reduce the power voltage of 3V to 2.7V for the following reasons.
1) The operational amplifier OPA2354 currently supplies ±3V power and 6V equivalent unipolar power. However, the official manual says the working voltage ranges from 2.5V to 5.5V. All the indicators on the manual are tested within this range. The manual also points out that if the unipolar power voltage exceeds 7.5V, the battery will suffer permanent damage. In a range from 5.5V to 7.5V, the quality of the internal components cannot be ensured. Consequently, the battery might be either functional or dysfunctional. Now the OPA2354’s operating voltage at 6V is within this range. When the power voltage reduces from 3V to 2.7V, the OPA2354’s supplying power voltage turns into 5.4V, which is in the safe working voltage range as recommended in TI’s manual.
2) The minimum operating voltage of the memory chip W25Q64 is 2.7V, which is a factor for restricting the operating voltage from continuing to fall. Additionally, the touch control chip has a minimum operating voltage of 2.5V. Other components such as the MCU, the OPA, the analog switches, and the charge pump can work at a voltage of 2V.
3) The power voltage of 3V is supplied by the 1st road DCDC of AXP192. The output voltage is adjustable. Since the AXP192 adopts switch buck, the output voltage can be bucked down to enhance the efficiency and extend the life cycle of a battery. The OPA negative power rail –V network derives from the inversion of 3V power. Automatic regulation of either the input voltage or the output voltage is available. The output voltage of the 3rd road LDO that offers the +V network is also adjustable. Adjustment is available through software.
4) As is found in the test, when the battery voltage reached 3V, the input signals of DS202 started to fluctuate violently. The reasons might be as follows. If the battery voltage hit 3V, the buck circuit on DCDC is equal to a direct circuit. Theoretically, it can provide a voltage of 3V, which means, the operational amplifier negative power rail –V network can keep a voltage of -3V. However, the positive power rail +V network is exported by LDO, so it cannot ensure an output of +3V. In brief, the OPA power supply cannot be guaranteed.
5) DS202 is designed with a voltage cap of 40V. The front is equipped with respectively a 1 M and a 75k resistance voltage divider. Therefore the maximum input voltage to the OPA is 40*75/(1000+75)=2.7907V. So, the ±3V power supply naturally suffices to meet the input voltage requirement. In fact, OPA2354 input voltage ranges from –V-0.1 to +V+0.1. In case of ±2.7V power supply, the input voltage varies from -2.8V to 2.8V. Theoretically, it is within the required voltage range.
| 
发表于 2015-8-3 10:55:13
发表于 2015-8-3 11:21:08