LTC2480CDD datasheet(19/40 Pages) LINER

19 / 40 page

LTC2480

2480f

When using the internal temperature sensor, if the output

code is normalized to RSDO = VPTAT/VREF, the temperature

is calculated using the following formula:

SLOPE

SDO

REF

SDO

REF

=°

•

–

in Kelvin

and

in C

273

where SLOPE is nominally 1.4mV/

°C.

Since the PTAT signal can have an initial value variation

which results in errors in SLOPE, to achieve better tem-

perature measurements, a one-time calibration is needed

to adjust the SLOPE value. The converter output of the

PTAT signal, R0SDO, is measured at a known temperature

T0 (in

°C) and the SLOPE is calculated as:

SLOPE

SDO

REF

0 273

•

This calibrated SLOPE can be used to calculate the

temperature.

If the same VREF source is used during calibration and

temperature measurement, the actual value of the VREF is

not needed to measure the temperature as shown in the

calculation below:

SLOPE

SDO

REF

SDO

()

•

–

•–

273

0 273

273

Reference Voltage Range

The LTC2480 external reference voltage range is 0.1V to

VCC. The converter output noise is determined by the

thermal noise of the front-end circuits, and as such, its

value in nanovolts is nearly constant with reference volt-

age. Since the transition noise (600nV) is much less than

the quantization noise (VREF/217), a decrease in the refer-

ence voltage will increase the converter resolution. A

reduced reference voltage will also improve the converter

performance when operated with an external conversion

clock (external FO signal) at substantially higher output

data rates (see the Output Data Rate section). VREF must

≥1.1V to use the internal temperature sensor.

The negative reference input to the converter is internally

tied to GND. GND (Pin 8) should be connected to a ground

plane through as short a trace as possible to minimize

voltage drop. The LTC2480 has an average operational

current of 160

µA and for 0.1Ω parasitic resistance, the

voltage drop of 16

µV causes a gain error of 3.2ppm for

VREF = 5V.

Input Voltage Range

The analog input is truly differential with an absolute/

common mode range for the IN+ and IN– input pins

extending from GND – 0.3V to VCC + 0.3V. Outside

these limits, the ESD protection devices begin to turn on

and the errors due to input leakage current increase

rapidly. Within these limits, the LTC2480 converts the

bipolar differential input signal, VIN = IN+ – IN–, from – FS

to +FS where FS = 0.5 • VREF/GAIN. Outside this range, the

converter indicates the overrange or the underrange con-

dition using distinct output codes. Since the differential

input current cancellation does not rely on an on-chip

buffer, current cancellation as well as DC performance is

maintained rail-to-rail.

Input signals applied to IN+ and IN– pins may extend by

300mV below ground and above VCC. In order to limit any

fault current, resistors of up to 5k may be added in series

with the IN+ and IN– pins without affecting the perfor-

mance of the devices. The effect of the series resistance

on the converter accuracy can be evaluated from the

curves presented in the Input Current/Reference Current

sections. In addition, series resistors will introduce a

APPLICATIO S I FOR ATIO

Figure 4. Internal PTAT Signal vs Temperature

TEMPERATURE (

°C)

–60

500

600

120

2480 F04

400

200

090

–30

300

VCC = 5V

IM = 1

FO = GND

SLOPE = 1.40mV/

°C

LTC2480CDD Datasheet(PDF) 19 Page - Linear Technology

LTC2480CDD Datasheet(HTML) 19 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Datasheet Download

Link URL