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REG102GA-2.85 Datasheet(PDF) 11 Page - Texas Instruments |
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REG102GA-2.85 Datasheet(HTML) 11 Page - Texas Instruments |
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11 / 20 page  REG102 11 SBVS024F www.ti.com FIGURE 6. Transient and DC Dropout. 350 300 250 200 150 100 50 0 0 50 100 150 200 DC 250 I OUT (mA) DROPOUT VOLTAGE vs I OUT 0mA to I OUT Transient DROPOUT VOLTAGE The REG102 uses an N-channel DMOS as the pass element. When (VIN – VOUT) is less than the drop-out voltage (VDROP), the DMOS pass device behaves like a resistor; therefore, for low values of (VIN – VOUT), the regulator input-to-output resistance is the RdsON of the DMOS pass element (typically 600m Ω). For static (DC) loads, the REG102 typically main- tains regulation down to a (VIN – VOUT) voltage drop of 150mV at full rated output current. In Figure 6, the bottom line (DC dropout) shows the minimum VIN to VOUT voltage drop re- quired to prevent dropout under DC load conditions. For large step changes in load current, the REG102 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 and values of VIN to VOUT voltage drop above this line insure normal transient re- sponse. case conditions (full-scale load change with (VIN – VOUT) voltage drop close to DC dropout levels), the REG102 can take several hundred microseconds to re-enter the specified window of regulation. TRANSIENT RESPONSE The REG102 response to transient line and load conditions improves at lower output voltages. The addition of a capacitor (nominal value 0.47 µF) from the output pin to ground can improve the transient response. In the adjustable version, the addition of a capacitor, CFB (nominal value 10nF), from the output to the adjust pin can also improve the transient response. THERMAL PROTECTION Power dissipated within the REG102 can cause the junction temperature to rise. The REG102 has thermal shutdown circuitry that protects the regulator from damage which dis- ables 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 out- put circuitry is again enabled. Depending on various condi- tions, the thermal protection circuit can cycle on and off. This limits the dissipation of the regulator, but can have an undesirable effect on the load. Any tendency to activate the thermal protection circuit indi- cates excessive power dissipation or an inadequate heat sink. For reliable operation, junction temperature must 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 reliabil- ity, thermal protection should trigger more than 35 °C above the maximum expected ambient condition of the application. This produces a worst-case junction temperature of 125 °C at the highest expected ambient temperature and worst-case load. The internal protection circuitry of the REG102 is designed to protect against overload conditions and is not intended to replace proper heat sinking. Continuously running the REG102 into thermal shutdown will degrade reliability. In the transient dropout region between DC and Transient, 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- |
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Similar Description - REG102GA-2.85 |
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