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DCR012403U Datasheet(PDF) 11 Page - Texas Instruments |
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DCR012403U Datasheet(HTML) 11 Page - Texas Instruments |
11 / 19 page DCR01 Series 11 SBVS013C ERROR FLAG The DCR01 has an ERROR pin which provides a “power good” flag, as long as the internal regulator is in regulation. DECOUPLING Ripple Reduction Due to the very low forward resistance of the DMOS switching transistors, high current demands are placed upon the input supply for a short time. By using a good quality low Equivalent Series Resistance (ESR) capacitor of 2.2 µF (minimum) for the 5V input devices and a 0.47 µF capacitor for the 12V and 24V devices, placed close to the IC supply input pins, the effects on the power supply can be mini- mized. The high switching frequency of 400kHz allows relatively small values of capacitors to be used for filtering the recti- fied output voltage. A good quality low ESR capacitor of 1 µF placed close to the V REC pin and output ground will reduce the ripple. It is not recommended that the DCR01 be fitted using an IC socket as this will degrade performance. The output at VREC is full wave rectified and produces a ripple of 800kHz. It is recommended that a 0.1 µF low ESR capacitor is connected close to the output pin and ground to reduce noise on the output. The capacitor values listed are minimum values. If lower ripple is required then the filter capacitor should be increased in value to 2.2 µF. NOTE: As with all switching power supplies the best performance is only obtained with low ESR capacitors connected close to the switcher. If low ESR capacitors are not used, the ESR will generate a voltage drop when the capacitor is supplying the load power. Often a larger capaci- tor is chosen for this purpose when a low ESR smaller capacitance would perform as well. APPLICATION NOTES DCR01 SINGLE VOLTAGE OUTPUT The DCR01 can be used to provide a single voltage output by connecting, see Figure 1. The ERROR output signal will be pulled up to the value of VOUT for the particular DCR01 being used. The value of RERR will depend on the loading on the ERROR line however, the total load on the ERROR line must not exceed the value given in the specification. The output may be permanently enabled by connecting the ENABLE pin to the VREC pin. The DCR01 may be enabled remotely by connecting the ENABLE pin to VREC via a pull- up resistor (REN ), the value of this resistor is not critical for the DCR01 as only a small current flows. The switch SW1 can be used to pull the ENABLE pin LOW, thus disabling the output. The switching devices can be a bipolar transistor, FET or a mechanical device, the main load that it will see is REN. GENERATING TWO POSITIVE OUTPUT VOLTAGES Two DCR01s can be used to create output voltages of +3.3V and +5V, as shown in Figure 2. The two DCR01s are connected in self-synchronization, thus locking the oscilla- tors of both devices to a single frequency. The ERROR and ENABLE facilities may be used in a similar configuration for a single DCR01. The filter capaci- tors connected to the VREC pins (CFILTER), should be kept separate from each other and connected in close proximity to their respective DCR01. If similar output voltages are being used, it is not recommended that a single filter capacitor (with an increased capacitance) be used with both VREC pins connected together, as this could result is the overloading of one of the devices. DCR 01 V OUT V IN C IN (1) C OUT = 0.1µF R ERR = 10kΩ C FILTER = 1µF V O1 0V ENABLE V REC ERROR V S U1 0V SYNC ERROR DCR 01 V OUT V IN C IN (1) C OUT = 0.1µF R ERR = 10kΩ C FILTER = 1µF V O2 0V ENABLE V REC ERROR V S U2 0V SYNC 0V OUT ERROR NOTE: (1) 2.2 µF capacitor with low ESR for 5V devices and 0.47 µF for 12V and 24V devices. FIGURE 2. Generating Two Positive Voltages from Self-Synchronized DCR01s. |
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