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TC2574-3.3VPA Fiches technique(PDF) 8 Page - TelCom Semiconductor, Inc |
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TC2574-3.3VPA Fiches technique(HTML) 8 Page - TelCom Semiconductor, Inc |
8 / 25 page TC2574 8 TC2574-1 1/6/00 0.5A Step-Down Switching Regulator Procedure (Fixed Output Voltage Version) (Continued) In order to simplify the switching regulator design, a step-by-step design procedure and examples are provided. Procedure Example 5. Output Capacitor Selection (COUT) A. Since the TC2574 is a forward–mode switching regulator with voltage mode control, its open loop 2–pole–1–zero frequency characteristic has the dominant pole–pair deter mined by the output capacitor and inductor values. For stable operation and an acceptable ripple voltage, (approximately 1% of the output voltage) a value between 100 µF and 470µF is recommended. B. Due to the fact that the higher voltage electrolytic capacitors generally have lower ESR (Equivalent Series Resistance) numbers, the output capacitor’s voltage rating should be at least 1.5 times greater than the output voltage. For a 5.0Vregulator, a rating at least 8.0V is a appropriate, and a 10Vor 16V rating is recommended. 5. Output Capacitor Selection (COUT ) A. COUT = 100µF to 470µF standard aluminium electrolytic. B. Capacitor voltage rating = 20V. Procedure (Adjustable Output Version: TC2574-ADJ) Procedure Example Given Parameters: VOUT = Regulated Output Voltage VIN (max) = Maximum DC Input Voltage ILOAD (max) = Maximum Load Current 1. Programming Output Voltage To select the right programming resistor R1 and R2 value (see Figure 2) use the following formula: VOUT = VREF (1.0 + R2 ) where V REF = 1.23V R1 Resistor R1 can be between 1.0k Ω and 5.0kΩ. (For best temperature coefficient and stability with time, use 1% metal film resitors). R2 = R1 ( VOUT – 1.0) VREF 2. Input Capacitor Selection (CIN ) To prevent large voltage transients from appearing at the input and for stable operation of the converter, an aluminium or tantalum electrolytic bypass capacitor is needed between the input pin +VIN and ground pin GND. This capacitor should be located close to the IC using short leads. This capacitor should have a low ESR (Equivalent Series Resistance) value. For additional information see input capacitor section in the “EXTERNAL COMPONENTS” section of this data sheet. Given Parameters: VOUT = 24V VIN (max) = 40V ILOAD (max) = 0.4A 2. Input Capacitor Selection (CIN ) A 22 µF aluminium electrolytic capacitor located near the input and ground pin provides sufficient bypassing. 1. Programming Output Voltage (selecting R1 and R2) Select R1 and R2 VOUT = 1.23 (1.0 + R2 ) Select R1 = 1.0kΩ R1 R2 = R1 ( VOUT – 1.0) = 1.0k ( 10V – 1.0) VREF 1.23V R1 = 18.51k Ω, choose a 18.7kΩ metal film resistor. |
Numéro de pièce similaire - TC2574-3.3VPA |
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Description similaire - TC2574-3.3VPA |
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