236AC1 데이터 시트보기 (PDF) - Linear Technology

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236AC1

Precision Reference

Linear Technology 

LT1236

APPLICATIONS INFORMATION

Kelvin Connections

Although the LT1236 does not have true force/sense

capability at its outputs, significant improvements in ground

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

line, greatly reducing ground loop and loss problems on

the low side of the reference. The high side supplies load

current so line resistance must be kept low. Twelve feet of

#22 gauge hook-up wire or 1 foot of 0.025 inch printed

circuit trace will create 2mV loss at 10mA output current.

This is equivalent to 1LSB in a 10V, 12-bit system.

The following circuits show proper hook-up to minimize

errors due to ground loops and line losses. Losses in the

output lead can be greatly reduced by adding a PNP boost

transistor if load currents are 5mA or higher. R2 can be

added to further reduce current in the output sense lead.

Effects of Air Movement on Low Frequency Noise

The LT1236 has very low noise because of the buried zener

used in its design. In the 0.1Hz to 10Hz band, peak-to-peak

noise is about 0.5ppm of the DC output. To achieve this

low noise, however, care must be taken to shield the

reference from ambient air turbulence. Air movement can

create noise because of thermoelectric differences be-

tween IC package leads and printed circuit board materials

and/or sockets. Power dissipation in the reference, even

though it rarely exceeds 20mW, is enough to cause small

temperature gradients in the package leads. Variations in

thermal resistance, caused by uneven air flow, create

differential lead temperatures, thereby causing thermo-

electric voltage noise at the output of the reference.

Standard Series Mode

INPUT

LT1236

IN

OUT

GND

KEEP THIS LINE RESISTANCE LOW

+

LOAD

GROUND

RETURN

LT1236 AI03

Series Mode with Boost Transistor

INPUT

R1

220Ω

2N3906

IN

LT1236

OUT

GND

LOAD

R2*

GROUND

RETURN

*OPTIONAL—REDUCES CURRENT IN OUTPUT SENSE

LEAD: R2 = 2.4k (LT1236-5), 5.6k (LT1236-10)

LT1236 AI04

TYPICAL APPLICATIONS

Restricted Trim Range for Improved

Resolution, 10V, “A” Version Only

LT1236A-10

VIN IN

OUT

GND TRIM R1

75k

10.000V

R2

50k

TRIM RANGE ≈ ±10mV

8

LT1236 TA10

LT1236-10 Full Trim Range (±0.7%)

LT1236-10

VIN IN

OUT

GND TRIM

VOUT

R1*

10k

LT1236 TA03

*CAN BE RAISED TO 20k FOR LESS

CRITICAL APPLICATIONS

Negative Series Reference

15V

R1

4.7k

LT1236-10

IN

OUT

R2

D1

GND

4.7k

15V

–15V

Q1

2N2905

–10V AT

50mA

LT1236 TA04

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