設計一個12V轉3.3V，輸出電流30mA的電源電路，由于項目對轉化效率要求較高，所以不能采用低壓差線性穩壓LDO的方案。經過對比，TOREX的XC9264效率在此轉化條件下效率可做到85%以上，比MPS等廠家同類型芯片效率做得高很多。

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特性：

　　輸入電壓范圍：3-18V（極限值20V）

　　FBVoltage: 0.75V

　　開關頻率：500kHz，1.2MHz，2.2MHz

　　輸出最大電流：0.5A

　　控制模式：PWM/PFM

　　軟啟動時間：由RC調節

　　保護：過流保護、內部鎖定機制、熱關機

　　輸出、輸入采用低ESR陶瓷電容

　　封裝：SOT-25，USP-6C

典型電路圖：

輸出電壓設定：Vout=Vfb*(Rfb1+Rfb2)/Rfb2　　（注意Rfb1+Rfb2<1Mohm）

相位補償加速電容(phase compensation speed-up capacitor)：Cfb=1/(2∏*fzfb*Rfb1)

軟啟動時間設定：通過增加一個電容和一個電阻給EN/SS腳

　　　　

內部結構框圖：

內部功能模塊：軟啟動電路、誤差放大器、PWM比較器、斜坡電路、振蕩器、相位補償電路、限流電路、PFM脈沖調制電路、高低側驅動、低電壓鎖定電路（UVLO）、門鉗位電路、熱關機電路（TSD）、內部供電電路?

工作模式：輸出電壓反饋至FB引腳，與誤差放大器比較后，誤差放大器輸出脈沖補償，該信號輸入PWM比較器，輸出信號至驅動緩沖電路，從LX輸出開關周期信號，從而穩定住電壓。

Reference voltage source:該參考電流源提供參考電壓確保輸出電壓穩定；

Oscillator circuit：斜坡電路決定了開關頻率，有500KHZ，1.2MHZ或者2.２MHZ;

為避免自已翻譯容易造成誤解，以下摘抄datasheet英文原文：

Current limiting:The current limiting circuit of the XC9263/64 series monitors the current that flows through the High-side driver transistor and Low-side driver transistor, and when over-current is detected, the current limiting function activates.
① Low-side driver Tr. current limiting
　　The current in the Low-side driver Tr. is detected to equivalently monitor the bottom value of the coil current. The Low-side driver Tr. current limiting function prohibits the High-side driver Tr. from turning on in an over-current state where the bottom value of the coil current is higher than the Low-side driver Tr. current limit value ILIML. Control to lower the switching frequency fOSC is also performed. When the over-current state is released, normal operation resumes.
② High-side driver Tr. current limiting
　　The current in the High-side driver Tr. is detected to equivalently monitor the peak value of the coil current. The High-side driver Tr. current limiting function forcibly turns off the High-side driver Tr. when the peak value of the coil current reaches the High-side driver current limit value ILIMH. ILIML < ILIMH is set inside the IC, and therefore the Low-side driver Tr. current limiting function of ① above also detects the over-current state at this time. When the over-current state is released, normal operation resumes.
③ Over-current latch (Type A)
　　Type A turns off the High-side and Low-side driver Tr. when state ① or ② continues for 1.0ms (TYP.). The LX pin is latch-stopped at the GND level (0V).

　　The latch-stopped state only stops the pulse output from the Lx pin; the internal circuitry of the IC continues to operate. To restart after latch-stopping, L level and then H level must be input into the EN/SS pin, or VIN pin re-input must be performed (after lowering the voltage below the UVLO detection voltage) to resume operation by soft start.
　　The over-current latch function may occasionally be released from the current limit detection state by the effects of ambient noise, and it may also happen that the latch time becomes longer or latching does not take place due to board conditions. For this reason, place the input capacitor as close as possible to the IC.

　　Type B is an automatic recovery type that performs the operation of ① or ② until the over-current state is released.

　　Low side driver Tr. current limit value ILIML=0.7A (TYP.)
　　High-side driver Tr. current limit value ILIMH=1.1A (TYP.)

Soft-start function:
　　The reference voltage applied to the error amplifier is restricted by the start-up voltage of the EN/SS pin. This ensures that the error amplifier operates with its two inputs in balance, thereby preventing ON-time signal from becoming longer than necessary. Therefore, start-up time of the EN/SS pin becomes the set-time of soft-start. The soft-start time can be adjusted by adding a capacitor and a resistor to the EN/SS pin.

　　If the EN/SS pin voltage rises steeply without connecting CSS and RSS (RSS=0?), Output rises with taking the soft-start time of tss1=1.0ms (TYP.) which is fixed internally.

　　The soft-start function operates when the voltage at the EN/SS pin is between 0.3V to 2.5V. If the voltage at the EN/SS pin does not start from 0V but from a middle level voltage when the power is switched on, the soft-start function will become ineffective and the possibilities of large inrush currents and ripple voltages occurring will be increased.

Thermal shutdown:
　　The thermal shutdown (TSD) as an over current limit is built in the XC9263/64 series.When the junction temperature reaches the detection temperature, the driver transistor is forcibly turned off. When the junction temperature falls to the release temperature while in the output stop state, restart takes place by soft-start.

UVLO:

　　When the VIN pin voltage falls below 2.7V (TYP.), the driver transistor is forcibly turned off to prevent false pulse output due to instableoperation of the internal circuits. When the VIN pin voltage rises above 2.8V (TYP.), the UVLO function is released, the soft-start function activates, and output start operation begins. Stopping by UVLO is not shutdown; only pulse output is stopped and the internal circuits continueto operate.

Power good:

　　On USP-6C Package, the output state can be monitored using the power good function.When the FB voltage drops below 90% (TYP.), the PG pin outputs an "L" signal.The PG pin is an Nch open drain output, therefore a pull-up resistance (approx. 100k?) must be connected to the PG pin.

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轉載于:https://www.cnblogs.com/CYP01/p/5943718.html

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