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CS8271YD8 データシート(PDF) 4 Page - Cherry Semiconductor Corporation |
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CS8271YD8 データシート(HTML) 4 Page - Cherry Semiconductor Corporation |
4 / 6 page 4 The output compensation capacitor COUT, determines three main characteristics of a linear regulator: start-up delay, load transient response and loop stability. The selection of a capacitor value and type should be based on cost, availability, size and temperature con- straints. A tantalum or aluminum electrolytic capacitor is best, since a film or ceramic capacitor with almost zero ESR, can cause instability. The aluminum electrolytic capacitor is the least expensive solution, but, if the circuit operates at low temperatures (-25¡C to -40¡C), both the value and ESR of the capacitor will vary considerably. The capacitor manufacturers data sheet usually provide this information. The value for the output compensation capacitor COUT shown in Figure 3 should work for most applications, but it is not necessarily the least expensive or the optimal solution. Figure 3: Test and application circuit showing an output compensation capacitor. To determine an acceptable value for COUT for a particular application, start with a tantalum capacitor of the recom- mended value and work towards a less expensive alterna- tive part. Step 1: Place the completed circuit with a tantalum capac- itor of the recommended value in an environmental cham- ber at the lowest specified operating temperature. Monitor the outputs on the oscilloscope. A decade box connected in series with the capacitor will simulate the higher ESR of an aluminum capacitor. (Leave the decade box outside the chamber, the small resistance added by the longer leads is negligible) Step 2: With the input voltage at its maximum value, increase the load current slowly from zero to full load while observing the output for any oscillations. If no oscil- lations are observed, the capacitor is large enough to ensure a stable design under steady state conditions. Step 3: Increase the ESR of the capacitor from zero using the decade box and vary the load current until oscillations appear. Record the values of load current and ESR that cause the greatest oscillation. This represents the worst case load conditions for the regulator at low temperature. Step 4 : Maintain the worst case load conditions set in step 3 and vary the input voltage until the oscillations increase. This point represents the worst case input voltage condi- tions. Step 5: If the capacitor is adequate, repeat steps 3 and 4 with the next smaller valued capacitor. (A smaller capaci- tor will usually cost less and occupy less board space.) If the capacitor oscillates within the range of expected oper- ating conditions, repeat steps 3 and 4 with the next larger standard capacitor value. Adj CS8271 VOUT RRST COUT 10 mF RL ENABLE VIN CIN 0.1 mF CAdj (optional) Selecting the Right Capacitor Value Application Notes The output stage is protected against overvoltage, short circuit and thermal runaway conditions (Figure 2). If the input voltage rises above 30V (e.g. load dump), the output shuts down. This response protects the internal cir- cuitry and enables the IC to survive unexpected voltage transients up to 60V in magnitude. Short circuit protection limits the amount of current the output transistor can supply. In the case of a CS8271 under a short circuit condition, the output transistor current is limited to 100mA. Figure 2: Typical Circuit Waveforms for Output Stage Protection. Should the junction temperature of the power device exceed 180ûC (typ) the power transistor is turned off. Thermal shut- down is an effective means to prevent die overheating since the power transistor is the principle heat source in the IC. The switches the output transistor. When the voltage on the pin exceeds 2.0V typ, the output pass transistor turns off, leaving a high impedance facing the load. The IC will remain in Sleep mode, drawing only 20µA (typ), until the voltage on the pin drops below the threshold. ENABLE ENABLE ENABLE ENABLE ENABLE IOUT VOUT VIN Load Dump Short Circuit Thermal Shutdown > 30V Output Stage Protection Circuit Description: continued |
同様の部品番号 - CS8271YD8 |
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同様の説明 - CS8271YD8 |
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