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## TC1221 Datasheet(PDF) 5 Page - Microchip Technology

 Part No. TC1221 Description High Frequency Switched Capacitor Voltage Converters with Shutdown in SOT Packages Download 16 Pages Scroll/Zoom 100% Maker MICROCHIP [Microchip Technology] Homepage http://www.microchip.com Logo

## TC1221 Datasheet(HTML) 5 Page - Microchip Technology

 5 / 16 page  2002 Microchip Technology Inc.DS21367B-page 5TC1221/TC12224.0APPLICATIONS INFORMATION4.1Output Voltage ConsiderationsThe TC1221/TC1222 perform voltage conversion butdo not provide regulation. The output voltage will droopin a linear manner with respect to load current. Thevalue of this equivalent output resistance is approxi-mately 25Ω nominal at +25°C and VIN = +5V. VOUT isapproximately -5V at light loads, and droops accordingto the equation below:VDROP = IOUT x ROUTVOUT = – (VIN – VDROP)4.2Charge Pump EfficiencyThe overall power efficiency of the charge pump isaffected by four factors:1.Losses from power consumed by the internaloscillator, switch drive, etc. (which vary withinputvoltage,temperatureandoscillatorfrequency).2.I2R losses due to the on-resistance of theMOSFET switches on-board the charge pump.3.Charge pump capacitor losses due to effectiveseries resistance (ESR).4.Losses that occur during charge transfer (fromthecommutationcapacitortotheoutputcapacitor) when a voltage difference betweenthe two capacitors exists.Most of the conversion losses are due to factors (2) and(3) above. These losses are given by Equation 4-1(b).EQUATION 4-1:The 1/(fOSC)(C1) term in Equation 4-1(b) is theeffective output resistance of an ideal switchedcapacitor circuit (Figure 4-1 and Figure 4-2). The valueof RSWITCH can be approximated at 0.5Ω for theTC1221/TC1222.The remaining losses in the circuit are due to factor (4)above, and are shown in Equation 4-2. The outputvoltage ripple is given by Equation 4-3.EQUATION 4-2:EQUATION 4-3:FIGURE 4-1:IDEAL SWITCHEDCAPACITOR MODELFIGURE 4-2:EQUIVALENT OUTPUTRESISTANCE4.3Capacitor SelectionIn order to maintain the lowest output resistance andoutput ripple voltage, it is recommended that low ESRcapacitors be used. Additionally, larger values of C1will lower the output resistance and larger values ofC2 will reduce output ripple. (Equation 4-1(b) andEquation 4-3).a) PLOSS (2, 3) = IOUT2 x ROUTb) where ROUT = [ 1 / [fOSC(C1) ] + 8RSWITCH +4ESRC1 + ESRC2]PLOSS(4) = [(0.5)(C1)(VIN2 – VOUT2)+ (0.5)(C2)(VRIPPLE2 – 2VOUT VRIPPLE)] xfOSCVRIPPLE =[ IOUT /2 x ( fOSC)(C2)] + 2 ( IOUT)(ESRC2)V+VOUTRLC2C1fV+VOUTREQUIVREQUIV =RLC2f x C11

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