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TPS71247DRCTG4 Datasheet(PDF) 11 Page - Texas Instruments |
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TPS71247DRCTG4 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 21 page P D + (VIN * VOUT) I OUT TPS71202, TPS71219 TPS71229, TPS71247 TPS71256, TPS71257 www.ti.com SBVS049D – MAY 2004 – REVISED AUGUST 2010 TRANSIENT RESPONSE enabled. Depending on power dissipation, thermal resistance, and ambient temperature, the thermal As with any regulator, increasing the size of the protection circuit may cycle on and off. This limits the output capacitor will reduce over/undershoot dissipation of the regulator, protecting it from damage magnitude but increase duration of the transient due to overheating. response. In the adjustable version, the addition of a capacitor, CFB, from the output to the feedback pin Any tendency to activate the thermal protection circuit will also improve stability and transient response. The indicates excessive power dissipation or an transient response of the TPS712xx is enhanced with inadequate heatsink. For reliable operation, junction an active pull-down that engages when the output is temperature should be limited to +125°C maximum. over-voltaged. The active pull-down decreases the To estimate the margin of safety in a complete design output recovery time when the load is removed. (including heatsink), increase the ambient Figure 13 in the Typical Characteristics section shows temperature until the thermal protection is triggered; the output transient response. use worst-case loads and signal conditions. For good reliability, thermal protection should trigger at least +35°C above the maximum expected ambient SHUTDOWN condition of your application. This produces a Both enable pins are active high and are compatible worst-case junction temperature of +125°C at the with standard TTL-CMOS levels. The device is only highest expected ambient temperature and completely disabled when both EN1 and EN2 are worst-case load. logic low. In this state, the LDO is completely off and The internal protection circuitry of the TPS712xx was the ground pin current drops to approximately 100 designed to protect against overload conditions. It nA. With one output disabled, the ground pin current was not intended to replace proper heatsinking. is slightly greater than half the nominal value. When Continuously running the TPS712xx into thermal shutdown capability is not required, the enable pins shutdown will degrade device reliability. should be connected to the input supply. POWER DISSIPATION INTERNAL CURRENT LIMIT The ability to remove heat from the die is different for The TPS712xx internal current limit helps protect the each package type, presenting different regulator during fault conditions. During current limit, considerations in the PCB layout. The PCB area the output will source a fixed amount of current that is around the device that is free of other components largely independent of the output voltage. moves the heat from the device to the ambient air. The TPS712xx PMOS-pass transistors have a built-in Performance data for a JEDEC high-K board is back diode that conducts reverse current when the shown in the Dissipation Ratings table. Using heavier input voltage drops below the output voltage (that is, copper will increase the effectiveness in removing during power-down). Current is conducted from the heat from the device. The addition of plated output to the input and is not internally limited. If through-holes to heat-dissipating layers will also extended reverse voltage operation is anticipated, improve the heat-sink effectiveness. external limiting may be appropriate. Power dissipation depends on input voltage and load conditions. Power dissipation (PD) is equal to the THERMAL PROTECTION product of the output current times the voltage drop Thermal protection disables both outputs when the across the output pass element (VIN to VOUT): junction temperature of either channel rises to (4) approximately +160°C, allowing the device to cool. When the junction temperature cools to Power dissipation can be minimized by using the approximately +140°C, the output circuitry is again lowest possible input voltage necessary to assure the required output voltage. Copyright © 2004–2010, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Link(s): TPS71202 TPS71219 TPS71229 TPS71247 TPS71256 TPS71257 |
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