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MIC2606YML Datasheet(PDF) 9 Page - Micrel Semiconductor |
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MIC2606YML Datasheet(HTML) 9 Page - Micrel Semiconductor |
9 / 14 page Micrel, Inc. MIC2605/6 September 2009 9 M9999-090909-B Functional Description The MIC2605/6 is a constant frequency, PWM current mode boost regulator. The block diagram is shown in Figure 1. The MIC2605/6 is composed of an oscillator, slope compensation ramp generator, current amplifier, gm error amplifier, PWM generator, and a 0.5A bipolar output transistor. The oscillator generates a 1.2MHz/ 2MHz clock. The clock’s two functions are to trigger the PWM generator that turns on the output transistor and to reset the slope compensation ramp generator. The current amplifier is used to measure the switch current by amplifying the voltage signal from the internal sense resistor. The output of the current amplifier is summed with the output of the slope compensation ramp generator. This summed current-loop signal is fed to one of the inputs of the PWM generator. The gm error amplifier measures the feedback voltage through the external feedback resistors and amplifies the error between the detected signal and the 1.25V reference voltage. The output of the gm error amplifier provides the voltage-loop signal that is fed to the other input of the PWM generator. When the current-loop signal exceeds the voltage-loop signal, the PWM generator turns off the bipolar output transistor. The next clock period initiates the next switching cycle, maintaining the constant frequency current-mode PWM control. Pin Description VIN VIN provides power to the MOSFETs for the switch mode regulator section. Due to the high switching speeds, a 1µF capacitor is recommended close to VIN and the power ground (PGND) pin for bypassing. Please refer to layout recommendations. VDD The VDD pin supplies the power to the internal power to the control and reference circuitry. The VDD is powered from VIN. A small 0.1µF capacitor is recommended for bypassing. EN The enable pin provides a logic level control of the output. In the off state, supply current of the device is greatly reduced (typically <0.1µA). Also, in the off state, the output drive is placed in a "tri-stated" condition, where bipolar output transistor is in an “off” or non- conducting state. Do not drive the enable pin above the supply voltage. SS The SS pin is the soft start pin which allows the monotonic buildup of output when the MIC2605/6 comes up during turn on. The SS pin gives the designer the flexibility to have a desired soft start by placing a capacitor SS to ground. A 0.1µF capacitor is used for in the circuit. FB The feedback pin (FB) provides the control path to control the output. For fixed output controller output is directly connected to feedback (FB) pin. SW The switch (SW) pin connects directly to the inductor and provides the switching current necessary to operate in PWM mode. Due to the high speed switching and high voltage associated with this pin, the switch node should be routed away from sensitive nodes. PGND Power ground (PGND) is the ground path for the high current PWM mode. The current loop for the power ground should be as small as possible and separate from the Analog ground (AGND) loop. Refer to the layout considerations for more details. VOUT VOUT pin is the cathode of pin of internal schottky diode. This pin is connected to output cap. At least 1µF cap is recommended very close to the VOUT pin and PGND. |
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