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REG113NA-3.33K Datasheet(PDF) 9 Page - Texas Instruments |
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REG113NA-3.33K Datasheet(HTML) 9 Page - Texas Instruments |
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9 / 16 page  REG113 9 SBVS031D www.ti.com OUTPUT NOISE A precision bandgap reference is used to generate the internal reference voltage, VREF. This reference is the domi- nant noise source within the REG113 and generates approxi- mately 29 µVrms in the 10Hz to 100kHz bandwidth at the reference output. The regulator control loop gains up the reference noise, so that the noise voltage of the regulator is approximately given by: V Vrms RR R Vrms V V N OUT REF =µ + =µ • 29 2 29 12 (1) Since the value of VREF is 1.26V, this relationship reduces to: V Vrms V V N OUT = µ • 23 (2) Connecting a capacitor, CNR, from the Noise Reduction (NR) pin to ground (as shown in Figure 3) forms a low-pass filter for the voltage reference. For CNR = 10nF, the total noise in the 10Hz to 100kHz bandwidth is reduced by approximately a factor of 2.8 for VOUT = 3.3V. This noise reduction effect is shown in Figure 4, and as RMS Noise Voltage vs CNR in the Typical Characteristics section. Noise can be further reduced by carefully choosing an output capacitor, COUT. Best overall noise performance is achieved with very low (< 0.22 µF) or very high (> 2.2µF) values of C OUT (see the RMS Noise Voltage vs COUT typical characteristic). The REG113 uses an internal charge pump to develop an internal supply voltage sufficient to drive the gate of the DMOS pass element above VIN. The charge-pump switching noise (nominal switching frequency = 2MHz) is not measur- able at the output of the regulator over most values of IOUT and COUT. DROPOUT VOLTAGE The REG113 uses an N-channel DMOS as the pass ele- ment. When (VIN – VOUT) is less than the dropout 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 REG113 will FIGURE 4. Output Noise versus Noise Reduction Capacitor. 0.1 100 1k 10 10k 110 100 90 80 70 60 50 40 30 20 C NR (pF) RMS NOISE VOLTAGE vs C NR REG113-5.0 REG113-3.3 REG113-2.5 C OUT = 0µF 10Hz < BW < 100kHz FIGURE 3. Block Diagram. Over-Current Over Temp Protection V REF (1.26V) Low-Noise Charge Pump DMOS Output V OUT NR GND Enable REG113 V IN C NR (optional) typically maintain regulation down to a (VIN – VOUT) voltage drop of 250mV at full rated output current. In Figure 5, the bottom line (DC dropout) shows the minimum VIN to VOUT voltage drop required to prevent dropout under DC load conditions. FIGURE 5. Transient and DC Dropout. 0 50 100 150 200 250 350 300 400 600 500 400 300 200 100 0 I OUT (mA) DROPOUT VOLTAGE vs I OUT Dropout for 0mA to I OUT Transient DC Dropout |
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