This article will show how XC9131H is used in parallel with an external power source to configure a "OR circuit". This proposed solution is simple because:
The number of external components is small (if the usage is allowed, even if LDO can be used).
In order to switch between the two power supplies, the signals of the EN and MODE pins of XC9131H are not required.
This explanation is not only suitable for XC9131H, but also for XC9135C, XC9135K and XC9136N. We will mention many VSET, VBAT, VEXT, and VOUT. The following is how to define these reference voltages: VSET: XC9131H Trial the output voltage set by the auxiliary resistor RFB1, RFB2, and internal reference voltage VREF. VBAT: The battery voltage supplied to XC9131H via the BAT pin.
Vext: Voltage from an external power supply. If LDO is used, the output voltage of the LDO is used. VOUT: OR circuit output output voltage. This is exactly the actual output voltage of the XC9131H circuit - and VSET is only the target value of the output voltage of XC9131H. When cutting the battery connected to the outside and VSET> VEXT, VSET is equal to VOUT.
Four voltages can be seen from the following circuit diagrams.
In the above circuit diagram, you can see EN = 'high' (IC enable) and modE = 'low' (IC is working in PWM / PFM mode). As mentioned in previous, do not need to adjust these voltage levels when the circuit works. We have three main situations:
B) The external power source is connected and the VSET having a voltage higher than the XC9131H will provide the output of the external power source. As previously described, the EN pin of XC9131H is 'high', so the XC9131H is working, but the voltage feedback to the XC9131H notifies that the IC output voltage is too high, so that IC basically stops oscillation (no longer send pulse to turn two An integrated field effect tube) and supplies output from XC6227.
C) VSET connected to an external power source and its voltage is below XC9131H In this case, the XC9131H detects that the output voltage is lower than the target Vset set by the feedback network. XC9131H starts working and supplies current to the output. Therefore, the voltage of the external power supply (if using an LDO, the voltage before the Vext is not the LDO) will be lower than VOUT, which means that the reverse current will flow. If an LDO is used, it is similar to the XC62227 that prevents the reverse current, and this current will not be worried about because the LDO and external power supplies will be protected. However, if the external power supply can receive a small amount of reverse current (if the external power supply is considered ideally adjusting the voltage), it can even increase the LDO.
FAQ (design restrictions)
Why can't the OR circuit when using XC9131F?
The XC9131 circuit is only used (that is, the external power supply is not used in parallel), it is recommended to replace the XC9131F with XC9131H, and the advantage is that since the function of adding the discharge of the CL is added. However, when the external power supply is included with the XC9131 circuit, the XC9131F is not guaranteed in the PFM mode. In fact, when its output voltage is lower than Vext, a P-channel driving transistor will be in turn on 'on', will allow the reverse current to flow from the external power source into the XC9131F. This reverse current will easily damage the XC9131F. Under the same conditions (PFM mode, vbat< VSet < Vext), XC9131H's P-channel drive will always be disconnected 'OFF', which means that the reverse current will never allow reverse current vout by IC The pin flows into the IC. This security behavior ensures that XC9131H uses OR circuits.
Why can't you set the Mode pin to 'high'?
By setting the MODE pin to 'high', XC9131H will completely operate in synchronous rectification PWM mode. In this mode, one of the two integrated field effectors is always turned on. This is why this configuration is not recommended. In fact, when Vext is higher than the output voltage set by XC9131H (remember, the rear man is Vset), the IC will reduce its duty cycle as much as possible to the output voltage to reduce the same voltage value as Vset.
Reducing the duty cycle means that the N-channel transistor is adjusted to the cut 'OFF', and since the transistor cannot be simultaneously cut ', the P-channel transistor will remain in' ON '. The result is that the reverse current can penetrate the XC9131H through its VOUT pin, and the internal circuits of the XC9131H are flowed and damaged by the P-channel transistors. In order to avoid this problem, set the MODE pin to 'Low' to operate the XC9131H in PWM / PFM mode, so that two transistors can be both 'OFF'. In such, it is possible to prevent the reverse current from entering XC9131H through the VOUT pin. It can be integrated with simple text, which can be considered that when VSET is lower than Vext, XC9131H is difficult to provide any current, so the load current is small.
Summary is summarized as follows: When the Mode pin is lower 'low', if the load current is small, the IC will work in the PFM mode. Because in PFM mode, and because VSET. 1881. Vext, P-channel transistors are always in 'OFF' and protect ICs are not affected by reverse current. When the MODE pin is at high 'high', if the load current is small, the IC will work in the PWM mode. In this mode, if the IC is oscillating at 1.2 MHz and the P-channel drive transistor is often turned on 'ON', some reverse current flows from VOUT into VBAT. Note: Of course, when the load current increases, such as XC9131H (its MODE pin is set to 'Low') is converted from PFM to PWM, and the reverse current will not be any problem. This is because when converted to a PWM mode, the XC9131H will work in a continuous conduction mode, so the reverse current will no longer appear.
Editor in charge: xj
Original title: How to use XC9131H in parallel with external power? Send super detailed solutions
Article Source: [WeChat public number: Torex product information] Welcome to add attention! Please indicate the source of the article. , Read full text, original title: How to use XC9131H with external power supply parallel? Send super detailed solutions
Article Source: [Micro Signal: GH_454737165C13, WeChat public number: Torex Product Information] Welcome to add attention! Please indicate the source of the article.
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