Datasheet LT1236 (Analog Devices) - 8
| Fabricante | Analog Devices |
| Descripción | Precision Reference |
| Páginas / Página | 12 / 8 — APPLICATIONS INFORMATION. Kelvin Connections. Standard Series Mode. … |
| Formato / tamaño de archivo | PDF / 230 Kb |
| Idioma del documento | Inglés |
APPLICATIONS INFORMATION. Kelvin Connections. Standard Series Mode. Series Mode with Boost Transistor
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Versión de texto del documento
LT1236
U U W U APPLICATIONS INFORMATION Kelvin Connections
temperature gradients in the package leads. Variations in thermal resistance, caused by uneven air flow, create Although the LT1236 does not have true force/sense differential lead temperatures, thereby causing thermo- capability at its outputs, significant improvements in ground electric voltage noise at the output of the reference. loop and line loss problems can be achieved with proper hook-up. In series mode operation, the ground pin of the LT1236 carries only ≈ 1mA and can be used as a sense
Standard Series Mode
line, greatly reducing ground loop and loss problems on the low side of the reference. The high side supplies load LT1236 KEEP THIS LINE RESISTANCE LOW current so line resistance must be kept low. Twelve feet of INPUT IN OUT + #22 gauge hook-up wire or 1 foot of 0.025 inch printed GND LOAD circuit trace will create 2mV loss at 10mA output current. This is equivalent to 1LSB in a 10V, 12-bit system. GROUND RETURN The following circuits show proper hook-up to minimize LT1236 AI03 errors due to ground loops and line losses. Losses in the output lead can be greatly reduced by adding a PNP boost
Series Mode with Boost Transistor
transistor if load currents are 5mA or higher. R2 can be INPUT added to further reduce current in the output sense lead. R1 220Ω 2N3906
Effects of Air Movement on Low Frequency Noise
The LT1236 has very low noise because of the buried zener IN used in its design. In the 0.1Hz to 10Hz band, peak-to-peak LT1236 noise is about 0.5ppm of the DC output. To achieve this OUT GND LOAD low noise, however, care must be taken to shield the R2* reference from ambient air turbulence. Air movement can create noise because of thermoelectric differences be- GROUND RETURN tween IC package leads and printed circuit board materials and/or sockets. Power dissipation in the reference, even *OPTIONAL—REDUCES CURRENT IN OUTPUT SENSE LEAD: R2 = 2.4k (LT1236-5), 5.6k (LT1236-10) though it rarely exceeds 20mW, is enough to cause small LT1236 AI04
U TYPICAL APPLICATIONS Restricted Trim Range for Improved LT1236-10 Full Trim Range (
±
0.7%) Negative Series Reference Resolution, 10V, “A” Version Only
15V LT1236-10 R1 LT1236A-10 LT1236-10 4.7k V IN IN OUT VOUT VIN IN OUT 10.000V IN OUT GND TRIM GND TRIM D1 R1 R2 GND R1* 15V 75k 4.7k R2 10k 50k –10V AT –15V Q1 50mA LT1236 TA03 2N2905 LT1236 TA04 TRIM RANGE *CAN BE RAISED TO 20k FOR LESS LT1236 TA10 ≈ ±10mV CRITICAL APPLICATIONS 8
U U W U APPLICATIONS INFORMATION Kelvin Connections
temperature gradients in the package leads. Variations in thermal resistance, caused by uneven air flow, create Although the LT1236 does not have true force/sense differential lead temperatures, thereby causing thermo- capability at its outputs, significant improvements in ground electric voltage noise at the output of the reference. loop and line loss problems can be achieved with proper hook-up. In series mode operation, the ground pin of the LT1236 carries only ≈ 1mA and can be used as a sense
Standard Series Mode
line, greatly reducing ground loop and loss problems on the low side of the reference. The high side supplies load LT1236 KEEP THIS LINE RESISTANCE LOW current so line resistance must be kept low. Twelve feet of INPUT IN OUT + #22 gauge hook-up wire or 1 foot of 0.025 inch printed GND LOAD circuit trace will create 2mV loss at 10mA output current. This is equivalent to 1LSB in a 10V, 12-bit system. GROUND RETURN The following circuits show proper hook-up to minimize LT1236 AI03 errors due to ground loops and line losses. Losses in the output lead can be greatly reduced by adding a PNP boost
Series Mode with Boost Transistor
transistor if load currents are 5mA or higher. R2 can be INPUT added to further reduce current in the output sense lead. R1 220Ω 2N3906
Effects of Air Movement on Low Frequency Noise
The LT1236 has very low noise because of the buried zener IN used in its design. In the 0.1Hz to 10Hz band, peak-to-peak LT1236 noise is about 0.5ppm of the DC output. To achieve this OUT GND LOAD low noise, however, care must be taken to shield the R2* reference from ambient air turbulence. Air movement can create noise because of thermoelectric differences be- GROUND RETURN tween IC package leads and printed circuit board materials and/or sockets. Power dissipation in the reference, even *OPTIONAL—REDUCES CURRENT IN OUTPUT SENSE LEAD: R2 = 2.4k (LT1236-5), 5.6k (LT1236-10) though it rarely exceeds 20mW, is enough to cause small LT1236 AI04
U TYPICAL APPLICATIONS Restricted Trim Range for Improved LT1236-10 Full Trim Range (
±
0.7%) Negative Series Reference Resolution, 10V, “A” Version Only
15V LT1236-10 R1 LT1236A-10 LT1236-10 4.7k V IN IN OUT VOUT VIN IN OUT 10.000V IN OUT GND TRIM GND TRIM D1 R1 R2 GND R1* 15V 75k 4.7k R2 10k 50k –10V AT –15V Q1 50mA LT1236 TA03 2N2905 LT1236 TA04 TRIM RANGE *CAN BE RAISED TO 20k FOR LESS LT1236 TA10 ≈ ±10mV CRITICAL APPLICATIONS 8