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TPS61221DCK Datasheet(PDF) 11 Page - Texas Instruments |
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TPS61221DCK Datasheet(HTML) 11 Page - Texas Instruments |
11 / 22 page DETAILED DESCRIPTION OPERATION CONTROLLER CIRCUIT I L t 200mA (typ.) ContinuousCurrentOperation DiscontinuousCurrentOperation 200mA (typ.) Device Enable and Shutdown Mode Startup Operation at Output Overload TPS61220 TPS61221 TPS61222 www.ti.com ............................................................................................................................................................................................... SLVS776 – JANUARY 2009 The TPS6122x is a high performance, high efficient family of switching boost converters. To achieve high efficiency the power stage is realized as a synchronous boost topology. For the power switching two actively controlled low RDSon power MOSFETs are implemented. The device is controlled by a hysteretic current mode controller. This controller regulates the output voltage by keeping the inductor ripple current constant in the range of 200 mA and adjusting the offset of this inductor current depending on the output load. In case the required average input current is lower than the average inductor current defined by this constant ripple the inductor current gets discontinuous to keep the efficiency high at low load conditions. Figure 23. Hysteretic Current Operation The output voltage VOUT is monitored via the feedback network which is connected to the voltage error amplifier. To regulate the output voltage, the voltage error amplifier compares this feedback voltage to the internal voltage reference and adjusts the required offset of the inductor current accordingly. At fixed output voltage versions an internal feedback network is used to program the output voltage, at adjustable versions an external resistor divider needs to be connected. The self oscillating hysteretic current mode architecture is inherently stable and allows fast response to load variations. It also allows using inductors and capacitors over a wide value range. The device is enabled when EN is set high and shut down when EN is low. During shutdown, the converter stops switching and all internal control circuitry is turned off. In this case the input voltage is connected to the output through the back-gate diode of the rectifying MOSFET. This means that there always will be voltage at the output which can be as high as the input voltage or lower depending on the load. After the EN pin is tied high, the device starts to operate. In case the input voltage is not high enough to supply the control circuit properly a startup oscillator starts to operate the switches. During this phase the switching frequency is controlled by the oscillator and the maximum switch current is limited. As soon as the device has built up the output voltage to about 1.8V, high enough for supplying the control circuit, the device switches to its normal hysteretic current mode operation. The startup time depends on input voltage and load current. If in normal boost operation the inductor current reaches the internal switch current limit threshold the main switch is turned off to stop further increase of the input current. In this case the output voltage will decrease since the device can not provide sufficient power to maintain the set output voltage. If the output voltage drops below the input voltage the backgate diode of the rectifying switch gets forward biased and current starts flow through it. This diode cannot be turned off, so the current finally is only limited by the remaining DC resistances. As soon as the overload condition is removed, the converter resumes providing the set output voltage. Copyright © 2009, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Link(s): TPS61220 TPS61221 TPS61222 |
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