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MIC2141 Datasheet(PDF) 6 Page - Micrel Semiconductor |
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MIC2141 Datasheet(HTML) 6 Page - Micrel Semiconductor |
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6 / 16 page  Micrel, Inc. MIC2141 December 2006 6 M9999-122006 Functional Diagram 330kHz FIXED DUTY CYCLE VC FB IN GND SW Oscillator MIC2141 Bandgap Reference Functional Description See “Applications Information” for component selection and pre-designed circuits. Overview This MIC2141 is a fixed-duty-cycle, constant-frequency, gated-oscillator, micropower, switch-mode power supply controller. Quiescent current for the MIC2141 is only 70µA in the switch off state, and since a MOSFET output switch is used, additional current needed for switch drive is minimized. Efficiencies above 85% throughout most operating conditions can be realized. Regulation Regulation is performed by a hysteretic comparator which regulates the output voltage by gating the internal oscillator. The user applies a programming voltage to the VC pin. (For a fixed or adjustable output regulator, with an internal reference, use the MIC2142.) The output voltage is divided down internally and then compared to the VC, the control input voltage, forcing the output voltage to 6 times the VC. The comparator has hysteresis built into it, which determines the amount of low frequency ripple that will be present on the output. Once the feedback input to the comparator exceeds the control voltage by 10mV, the high-frequency oscillator drive is removed from the output switch. As the feedback input to the comparator returns to the control voltage level, the comparator is reset and the high-frequency oscillator is again gated to the output switch. Typically 10mV of hysteresis seen at the comparator will correspond to 60mV of low-frequency ripple at the output. Applications, which require continuous adjustment of the output voltage, can do so by adjustment of the VC control pin. Output The maximum output voltage is limited by the voltage capability of the output switch. Output voltages up to 22V can be achieved with a standard boost circuit. Higher output voltages require a flyback configuration. Output Voltage Control The internal hysteretic comparator disables the output drive once the output voltage exceeds the nominal by 30mV. The drive is then enabled once the output voltage drops below the nominal by 30mV. The reference level, which actually programs the output voltage, is set by the VC control input. The output is 6 times the control voltage (VC) and the output ripple will be 6 times the comparator hystersis. Therefore, with 10mV of hystersis, there will be ±30mV variation in the output around the nominal value. See the “Typical Characteristics: Control Voltage vs. Output Voltage” for a graph of input-to-output behavior. The common-mode range of the comparator requires that the maximum control voltage (VC) be held to 200mV less than VIN. When programming for a 20V output, a minimum VIN of 3.5V will be required. See the “Typical Characteristics: Gain vs. Output Voltage” for a graph of gain behavior. To achieve 20V output at lower input voltages, the external resistive divider (R1 and R2) shown in Figure 2 can be added. This circuit will increase the control-to-output gain, while limiting the error introduced by the tolerance of the internal resistor feedback network. |
Similar Part No. - MIC2141_06 |
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Similar Description - MIC2141_06 |
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