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REG102GA-2.8G4 Datasheet(PDF) 10 Page - Burr-Brown (TI) |
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REG102GA-2.8G4 Datasheet(HTML) 10 Page - Burr-Brown (TI) |
10 / 23 page REG102 10 SBVS024F www.ti.com FIGURE 4. Block Diagram. FIGURE 5. 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 REG102-5.0 REG102-3.3 REG102-2.5 C OUT = 0µF 10Hz < BW < 100kHz Over-Current Over Temp Protection V REF (1.26V) Low-Noise Charge Pump DMOS Output R 1 NOTE: R 1 and R2 are internal on fixed output versions. V OUT Adj (adjustable versions) R 2 NR (fixed output versions only) Enable REG102 V IN C NR (optional) ENABLE The Enable pin is active high and compatible with standard TTL-CMOS levels. Inputs below 0.5V (max) turn the regula- tor off and all circuitry is disabled. Under this condition, ground pin current drops to approximately 10nA. When not used, the Enable pin can be connected to VIN. When a pull- up resistor is used, and operation below 1.8V is required, use pull-up resistor values below 50k Ω. 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 REG102 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) As 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 forms a low-pass filter for the voltage refer- ence. Adding CNR (as shown in Figure 4) forms a low-pass filter for the voltage reference. For CNR = 10nF, the total noise in the 10Hz to 100kHz bandwidth is reduced by approxi- mately a factor of 2.8 for VOUT = 3.3V. This noise reduction effect is shown in Figure 5 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 REG102 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. The REG102 adjustable version does not have the noise- reduction pin available; however, the adjust pin is the sum- ming junction of the error amplifier. A capacitor, CFB, con- nected from the output to the adjust pin can reduce both the output noise and the peak error from a load transient (see the typical characteristics for output noise performance). |
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