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REG101UA-5 Datasheet(PDF) 11 Page - Texas Instruments |
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REG101UA-5 Datasheet(HTML) 11 Page - Texas Instruments |
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11 / 18 page  REG101 11 SBVS026D FIGURE 6. Transient and DC Dropout. DROP-OUT VOLTAGE The REG101 uses an N-channel DMOS as the “pass” element. When the input voltage is within a few tens of millivolts of the output voltage, the DMOS device behaves like a resistor. Therefore, for low values of VIN to VOUT, the regulator’s input-to-output resistance is the RdsON of the DMOS pass element (typically 600m Ω). For static (DC) loads, the REG101 will typically maintain regulation down to VIN to VOUT voltage drop of 60mV at full rated output current. In Figure 6, the bottom line (DC dropout) shows the minimum VIN to VOUT voltage drop required to prevent drop-out under DC load conditions. For large step changes in load current, the REG101 requires a larger voltage drop across it to avoid degraded transient response. The boundary of this “transient drop-out” region is shown as the top line in Figure 6. Values of VIN to VOUT voltage drop above this line insure normal transient re- sponse. In the transient dropout region between “DC” and “Tran- sient”, transient response recovery time increases. The time required to recover from a load transient is a function of both the magnitude and rate of the step change in load current and the available “headroom” VIN to VOUT voltage drop. Under worst-case conditions (full-scale load change with VIN to VOUT voltage drop close to DC dropout levels), the REG101 can take several hundred microseconds to re-enter the speci- fied window of regulation. TRANSIENT RESPONSE The REG101 response to transient line and load conditions improves at lower output voltages. The addition of a capaci- tor (nominal value 0.47 µF) from the output pin to ground may improve the transient response. In the adjustable ver- sion, the addition of a capacitor, CFB (nominal value 10nF), from the output to the adjust pin will also improve the transient response. THERMAL PROTECTION The REG101 has thermal shutdown circuitry that protects the regulator from damage. The thermal protection circuitry disables the output when the junction temperature reaches approximately 160 °C, allowing the device to cool. When the junction temperature cools to approximately 140 °C, the output circuitry is again enabled. Depending on various conditions, the thermal protection circuit may cycle on and off. This limits the dissipation of the regulator, but may have an undesirable effect on the load. Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate heat sink. For reliable operation, junction temperature should be limited to 125 °C, maximum. To estimate the margin of safety in a complete design (including heat sink), increase the ambient temperature until the thermal protection is triggered. Use worst-case loads and signal conditions. For good reliability, thermal protection should trigger more than 35 °C above the maximum expected ambient condition of your application. This produces a worst-case junction tem- perature of 125 °C at the highest expected ambient tempera- ture and worst-case load. The internal protection circuitry of the REG101 has been designed to protect against overload conditions. It was not intended to replace proper heat sinking. Continuously run- ning the REG101 into thermal shutdown will degrade reli- ability. 140 120 100 80 60 40 20 0 0 25 50 75 100 150 125 I OUT (mA) DC Full Scale I OUT Transient |
Similar Part No. - REG101UA-5 |
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Similar Description - REG101UA-5 |
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