MAX35101 datasheet(13/66 Pages) AD

13 / 66 page

Temperature Measurement Operations

A temperature measurement is a time measurement of

the RC circuit connected to the temperature port device

pins T1 through T4 and TC. The TC device pin has a

driver to charge the timing capacitor. The ports that are

measured and the order in which the measurement is

performed is selected with the TP[1:0] bits in the Event

Timing 2 register.

Figure 6 depicts a 1000Ω platinum RTD with a 100nF

NPO COG 30ppm/°C capacitor. It shows two dummy

cycles with 4 temperature port evaluation measurements

and 4 real temperature port measurements. This occurs

when setting the TP[1:0] bits in the Event Timing 2 regis-

ter to 11b.

The dummy 1 and dummy 2 cycles represent preamble

measurements that are intended to eliminate the dielec-

tric absorption of the temperature measurement capaci-

tor. These dummy cycles are executed using a RTD

Emulation resistor of 1000Ω internal to the MAX35101.

This dummy path allows the dielectric absorption effects

of the capacitor to be eliminated without causing any of

the RTDs to be unduly self-heated. The number of dummy

measurements to be taken ranges from 0 to 7. This

parameter is configured by setting the PRECYC[2:0] bits

in the Event Timing 2 register.

Following the dummy cycles, an evaluation, TXevaluate,

is performed. This measurement allows the MAX35101

to maximize power efficiency by evaluating the tempera-

ture of the RTDs with a coarse measurement prior to a

real measurement. The coarse measurement provides

an approximation to the TDC converter. During the real

measurement, the TDC can then optimize its measure-

ment parameters to use power efficiently. These evaluate

cycles are automatically inserted according to the order of

ports selected with the of the Temperature Port bits. The

time from the start of one port’s temperature measure-

ment to the next port’s temperature measurement is set

using with the PORTCYC[1:0] bits in the Event Timing 2

Once all the temperature measurements are completed,

the times measured for each port are reported in the cor-

responding TxInt and TxFrac Results registers. The TE bit

in the Interrupt Status register is also set and the INT pin

asserts (if enabled).

Actual temperature is determined by a ratiometric calcu-

lation. If T1 and T2 are connected to platinum RTDs and

T3 and T4 are connected to the same reference resistor

(as shown in the System Diagram), then the ratio of T1/

T3 = RRTD1/RREF and T2/T4 = RRTD2/RREF. The ratios

RRTD1/RREF and RRTD2/RREF can be determined by the

host microprocessor and the temperature can be derived

from a look-up table of Temperature vs. Resistance for

each of the RTDs utilizing interpolation of table entries if

required.

Figure 6. Temperature Command Execution Cycle Example

DUMMY1

DUMMY2 T1EVALUATE T3EVALUATE T2EVALUATE T4EVALUATE

0.5

1.0

1.5

2.0

2.5

3.0

3.5

128

256

384

512

640

768

896

1,024

1,152

1,280

1,408

PORTCYCLE TIME

(PORTCYC1-PORTCYC0)

SET TO “00” 128µs

DRIVER TO CHANGE

TC-CONNECTED CAPACITOR

VTC

VOLTS (V)

VTC

TIME (µs)

Figure 6

MAX35101

Time-to-Digital Converter with Analog Front-End

www.maximintegrated.com

Maxim Integrated │ 13

MAX35101 Datasheet(PDF) 13 Page - Analog Devices

MAX35101 Datasheet(HTML) 13 Page - Analog Devices

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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66

Datasheet Download

Link URL