Datasheet LT6650 (Analog Devices) - 9
| Fabricante | Analog Devices |
| Descripción | Micropower, 400mV Reference with Rail-to-Rail Buffer Amplifier in SOT-23 |
| Páginas / Página | 12 / 9 — APPLICATIO S I FOR ATIO. Output Adjustment. Noise Reduction Capacitor. … |
| Formato / tamaño de archivo | PDF / 458 Kb |
| Idioma del documento | Inglés |
APPLICATIO S I FOR ATIO. Output Adjustment. Noise Reduction Capacitor. Shunt Reference Operation
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LT6650
U U W U APPLICATIO S I FOR ATIO
step between 100µA and 200µA in Figure 7. Load step settling contribution <0.15%). Since the VOUT error distribution occurs in about 0.5ms or less (to ±0.2%). increases at twice the resistor tolerance, high accuracy resistors or resistor networks are recommended. The
Output Adjustment
output voltage may be set to any level from 400mV up to If the LT6650 is to be used as a 400mV reference, then the 350mV below the supply voltage with source or sink output and feedback pins may be tied together without any capability. scale-setting components as shown in the front-page
Noise Reduction Capacitor
application circuit. Setting the output to any higher voltage is a simple matter of selecting two feedback resistors to In applications involving the use of resistive feedback for configure the non-inverting gain of the internal operational reference scaling, the intrinsic reference noise is amplified amplifier, as shown in Figure 8. A feedback resistor RF is along with the DC level. To minimize noise amplification, connected between the OUT pin and the FB pin, and a gain the use of a 1nF feedback capacitor is recommended, as resistor RG is connected from the FB pin to GND. The shown in Figure 8 and other circuits with scaling resistors. resistor values are related to the output voltage by the following relationship:
Shunt Reference Operation
R The circuits shown in Figure 9 and Figure 10 form adjust- F = RG • (VOUT – 0.4)/(0.4 – IFB • RG) able shunt references. Along with the external bias resistor The IFB term represents the FB pin bias current, and can R generally be neglected when R B, the LT6650 provides positive or negative reference G is 100k or less. For operation for outputs between 1.4V and 18V (positive or RG ≤ 20k, even worst-case IFB can be neglected (error negative). Just like a Zener diode, a supply VS is required, somewhat higher in magnitude than the desired reference V V S OUT 10mV/DIV AC RB VOUT = 0.4V • (1 + RF/RG) VOUT 4 5 1nF R IN OUT F 1 IOUT LT6650 FB 10µF 200µA GND RG 100µA 2 6650 F09 6650 F07
Figure 7. Output Response to Current-Sinking Load Step Figure 9. Typical Configuration of LT6650 as Adjustable Positive (100
µ
A to 200
µ
A) Shunt Reference
4 5 1nF 1k VOUT = 0.4V • (1 + RF/RG) R IN OUT F V V S OUT 1 4 5 1nF LT6650 FB 10µF R IN OUT F GND 1 RG 1µF LT6650 FB 1µF 2 VOUT GND RG V 2 R OUT = –0.4V • (1 + RF/RG) B 6650 F08 –VS 6650 F10
Figure 8. Typical Configuration for Output Voltages Figure 10. Typical Configuration of LT6650 as Adjustable Greater than 0.4V Negative Shunt Reference
6650fa 9
U U W U APPLICATIO S I FOR ATIO
step between 100µA and 200µA in Figure 7. Load step settling contribution <0.15%). Since the VOUT error distribution occurs in about 0.5ms or less (to ±0.2%). increases at twice the resistor tolerance, high accuracy resistors or resistor networks are recommended. The
Output Adjustment
output voltage may be set to any level from 400mV up to If the LT6650 is to be used as a 400mV reference, then the 350mV below the supply voltage with source or sink output and feedback pins may be tied together without any capability. scale-setting components as shown in the front-page
Noise Reduction Capacitor
application circuit. Setting the output to any higher voltage is a simple matter of selecting two feedback resistors to In applications involving the use of resistive feedback for configure the non-inverting gain of the internal operational reference scaling, the intrinsic reference noise is amplified amplifier, as shown in Figure 8. A feedback resistor RF is along with the DC level. To minimize noise amplification, connected between the OUT pin and the FB pin, and a gain the use of a 1nF feedback capacitor is recommended, as resistor RG is connected from the FB pin to GND. The shown in Figure 8 and other circuits with scaling resistors. resistor values are related to the output voltage by the following relationship:
Shunt Reference Operation
R The circuits shown in Figure 9 and Figure 10 form adjust- F = RG • (VOUT – 0.4)/(0.4 – IFB • RG) able shunt references. Along with the external bias resistor The IFB term represents the FB pin bias current, and can R generally be neglected when R B, the LT6650 provides positive or negative reference G is 100k or less. For operation for outputs between 1.4V and 18V (positive or RG ≤ 20k, even worst-case IFB can be neglected (error negative). Just like a Zener diode, a supply VS is required, somewhat higher in magnitude than the desired reference V V S OUT 10mV/DIV AC RB VOUT = 0.4V • (1 + RF/RG) VOUT 4 5 1nF R IN OUT F 1 IOUT LT6650 FB 10µF 200µA GND RG 100µA 2 6650 F09 6650 F07
Figure 7. Output Response to Current-Sinking Load Step Figure 9. Typical Configuration of LT6650 as Adjustable Positive (100
µ
A to 200
µ
A) Shunt Reference
4 5 1nF 1k VOUT = 0.4V • (1 + RF/RG) R IN OUT F V V S OUT 1 4 5 1nF LT6650 FB 10µF R IN OUT F GND 1 RG 1µF LT6650 FB 1µF 2 VOUT GND RG V 2 R OUT = –0.4V • (1 + RF/RG) B 6650 F08 –VS 6650 F10
Figure 8. Typical Configuration for Output Voltages Figure 10. Typical Configuration of LT6650 as Adjustable Greater than 0.4V Negative Shunt Reference
6650fa 9