Before entering the topic, you will introduce a schematic and the device involved, and our theme will also be blue from the characteristics of the core devices used in it. If you want to design an electronic device with a USB-C interface, you need this interface to identify a variety of different devices source and charge it to it in the correct way, and charge it on the internal battery. This picture is very valuable.
The core element RTQ 2115c in the figure consists of a C-type USB downlink port controller, a charging port controller, a USB 2.0 high-speed data line switch and 36V, 3.5A synchronous Buck converter, which can connect to the device using the USB-C interface. The incident is detected and arranged to implement the power supply operation, which is fully compliant. When it is in accordance with the USB 2.0 BC1.2 and the IF / T1591-2009 standard and the device access to Divider3 and 1.2V mode, it can detect the D + / D to D + / D in the data cable and automatically determine the specifications of its compliance. Automatically arrange power operations that match their specifications to achieve their charging process, which makes it easy to compatibility with most portable equipment that have already appeared in history, making your design extremely universally adaptability.
The RTQ 2115C contains synchronous Buck converters operate within 3V ~ 36V input voltage range, up to 42V voltage impact. Its rated operating frequency is 2.1MHz, which accepts 300kHz to 2.2 MHz external synchronization signal controlling its work rhythm. When it is used as a source of operating frequency, an external logic signal can control it into the spectral expansion mode, which can greatly reduce the difficulty of the electromagnetic compatibility problem, this mode will be at 2.1MHz ~ 2.1 Randomly beat in the range of MHz + 6%. When the load is light, its working mode can be selected as PSM or FPWM, which can meet the application requirements of high efficiency and high output voltage adjustment rate, respectively. Its output uses a CC / CV control method. When it works in a CV mode, it is very compliant with the demand for charging applications, and it can also use cable pressure drop compensation function to perform voltage drop on long line transmission. Compensation, avoiding fluctuations in the voltage of the load end.
The pin arrangement of RTQ2115c is the result of FMEA, the failure mode and its influence analysis, and the adjacent pin is short-circuited. It can avoid serious problems such as smoke, combustion. Its encapsulation pins have side wettable capabilities. The welded material flowing during welding can be wrapped in the side, and the improvement of welding reliability can be used, and it is also convenient to automatically discover the welding problem with the photoelectric detection method.
The RTQ 2115C is actually developed for the application requirements of the vehicle electronic device, and has passed the AEC-Q100 Grade 1 certification, which can be reliably operated within the temperature range of -40 ° C to 125 ° C.
Let's talk about how the RTQ2115c contains the Buck converter to implement CC / CV control and cable pressure drop compensation.
This is a schematic of the application circuitry involved in achieving CC / CV control and cable pressure drop compensation.
The feedback voltage Vfb obtained by the output voltage sampling circuit composed of R1 and R2 is sent to the voltage error amplifier, and the error is converted to a current output to adjust the voltage of the COMP end after the error is enlarged. The resulting voltage is again adjusted. The triangular wave synchronized with the clock signal is compared to the PWM signal that controls the switching action, and finally obtains a stable output voltage, CV control is completed.
The CC is constant current control is a controllable current source to make the COMP voltage in the above-described control loop with a controllable current source in the load current exceeds the preset current limit, which makes it increasing as the output current increases. Low, no matter the high output voltage at all. This behavior does not happen when the load current is not exceeding the limit, so it does not conflict with the CV control. In the circuit shown above, RSENSE is such an output current sampling resistor, and the CSP / CSN is connected inside the CSP / CSN is an error amplifier using a 100 mV reference voltage to compare objects, and its output is introduced in the following picture, we can It is integrated with the CMP node of the CV control loop, but its role is much stronger than the CV control error amplifier, which enables the output of the CV control error amplifier.
Now how cable pressure drop compensation is implemented. When the load current IOUT flows through the resistor RSENSE, a voltage difference VCS = RSENSE X IOUT is formed, and the voltage difference is processed after the internal circuit is processed, forming a current ILC (μA) = 21 x (VCS - 0.00476), between them The relationship is shown below:
This current is processed by the voltage feedback resistor network, and then adds an offset amount Vo_offset = ILC X R1 = 21 x (RSENSE X IOUT - 0.00476) X 10-6 X R1, so that the output voltage will carry The increase in current is automatically rising, but the voltage at the load connection is basically unchanged because the index of this offset is proposed according to the characteristics of the load line. Therefore, the actual design process needs to first give the offset indicator, then calculate the value of R1 according to the following formula:
The IOUT is the maximum load current in the application, and RSENSE is the resistance value of 100 mV voltage drop when this maximum load current flow is generated by resistance RSENSE.
Finally, according to the no-load output voltage value VOUT, the constant voltage controlled feedback reference voltage value VREF_CV = 0.8V and the value of the feedback resistor R2 are calculated:
RSENSE flows through a large current, and if the parameter needs to consider its power dissipation capability, the specific calculation formula is not involved here, and its wealth must be considered to ensure safety.
All formulas involved in this article have occurred in the specification of RTQ 2115c, and there is a problem with the readers to further reference to obtain the first hand information. Click on the original text to come quickly.
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