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LM22678QTJE-ADJ bảng dữ liệu(PDF) 7 Page - Texas Instruments |
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LM22678QTJE-ADJ bảng dữ liệu(HTML) 7 Page - Texas Instruments |
7 / 23 page LOGIC OSC + - TYPE III COMP + - 1.285V & Soft-start INT REG, EN,UVLO GND SW BOOT VIN EN FB VIN VOUT Error Amp. PWM Cmp. Vcc ILimit LM22678 www.ti.com SNVS585K – SEPTEMBER 2008 – REVISED MARCH 2013 Simplified Block Diagram Figure 11. Simplified Block Diagram Detailed Operating Description The LM22678 incorporates a voltage mode constant frequency PWM architecture. In addition, input voltage feed- forward is used to stabilize the loop gain against variations in input voltage. This allows the loop compensation to be optimized for transient performance. The power MOSFET, in conjunction with the diode, produce a rectangular waveform at the switch pin, that swings from about zero volts to VIN. The inductor and output capacitor average this waveform to become the regulator output voltage. By adjusting the duty cycle of this waveform, the output voltage can be controlled. The error amplifier compares the output voltage with the internal reference and adjusts the duty cycle to regulate the output at the desired value. The internal loop compensation of the -ADJ option is optimized for outputs of 5V and below. If an output voltage of 5V or greater is required, the -5.0 option can be used with an external voltage divider. The minimum output voltage is equal to the reference voltage; 1.285V (typ.). The functional block diagram of the LM22678 is shown in Figure 11 . Precision Enable and UVLO The precision enable input (EN) is used to control the regulator. The precision feature allows simple sequencing of multiple power supplies with a resistor divider from another supply. Connecting this pin to ground or to a voltage less than 1.6V (typ.) will turn off the regulator. The current drain from the input supply, in this state, is 25 µA (typ.) at an input voltage of 12V. The EN input has an internal pull-up of about 6 µA. Therefore this pin can be left floating or pulled to a voltage greater than 2.2V (typ.) to turn the regulator on. The hysteresis on this input is about 0.6V (typ.) above the 1.6V (typ.) threshold. When driving the enable input, the voltage must never exceed the 6V absolute maximum specification for this pin. Copyright © 2008–2013, Texas Instruments Incorporated Submit Documentation Feedback 7 Product Folder Links: LM22678 |
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