MAX1359B Maxim Integrated Products, MAX1359B Datasheet - Page 30

• Manufacturer Part Number: MAX1359B
• Description: Data-Acquisition System
• Manufacturer: Maxim Integrated Products

DataSheet.in
The internal temperature sensor measures die tempera-
ture and the external temperature sensor measures
remote temperatures. Use the internal temperature sen-
sor or external temperature sensor (remote transistor/
diode) with the ADC and internal current sources to
measure the temperature. For either method, two to four
currents are passed through a p-n junction and sense
resistor, and its temperature is calculated by a µC
using the diode equation and the forward-biased junc-
tion voltage drops measured by the ADC. The tempera-
ture offset between the internal p-n junction and
ambient is negligible. For the four and eight measure-
ment methods, the ratio of currents used in the diode
calculations is precisely known since the ADC mea-
sures the resulting voltage across the same sense
resistor. See Figure 13 for a block diagram of the tem-
perature sensor.
16-Bit, Data-Acquisition System with ADC, DAC,
UPIOs, RTC, Voltage Monitors, and Temp Sensor
Figure 13. Temperature-Sensor Measurement Block Diagram
30
AIN1
AIN2
______________________________________________________________________________________
IMUX<1:0>
IVAL<1:0>
PROGRAMMABLE CURRENT SOURCE
TEMP SENSOR
Temperature Sensor
CURRENT
SOURCE
DEMUX
1:3
AIN1
AIN2
TEMP+
TEMP-
For the two-current method, currents I
passed through a p-n junction. This requires two V
measurements. Temperature measurements can be
performed using I
where k is Boltzman’s constant. A four-measurement
procedure is adopted to improve accuracy by precisely
measuring the ratio of I
1) Current I
2) For the same current, the voltage across the diode
3) Repeat steps 1 and 2 with I
Since only four integer numbers are accessible from the
ADC conversions at a certain voltage reference, the previ-
ous equation can be represented in the following manner:
where N
ment results in integer format and V
voltage used in the ADC measurements.
The four-current method is used to account for the
diode series resistance and trace resistance. The four
currents are defined as follows; I
the currents are selected so (M
effect of the series resistance is eliminated from the
temperature measurements. For the currents I
and I
M
and I
current method, two measurements per current are
used to improve accuracy by precisely measuring the
values of the currents.
1) Current I
2) For the same current, the voltage across the diode and
2
resistor R, and the voltage across the diode is mea-
sured as V
and R is measured as V
I
resistor R, and the voltage is measured across the
diode using the ADC as NVBE1.
the series resistor is measured by the ADC as NV1.
2
= 2. This results in the currents I
2
4
is typically 60µA (see Table 21).
= 60µA, the factors are selected as M
= M
T
V1
MEAS
, N
2
1
1
I
2
is driven through the diode and the series
is driven through the diode and the series
BE1
V2
= 120µA (typ). As in the case of the two-
T
=
, N
MEAS
.
1
nk
and I
VBE1
q N
(
ln
1
=
VBE
⎛
⎜
⎝
, and N
2
and I
.
N
N
1
q V
V
V
2
.
(
2
1
nk
−
2
BE
−
−
:
N
2
N
N
1
. I
VBE2
VBE
2
ln
1
VBE
VBE
Four-Current Method
Two-Current Method
- 1)I
, I
1
−
⎛
⎜
⎝
I
I
2
V
is typically 4µA and
REF
2
1
1
1
2
, M
BE
)
⎞
⎟
⎠
1
are the measure-
3
⎞
⎟
⎠
1
= (M
1
×
is the reference
= M
)
I
1
V
1
2
, and M
REF
16
2
and I
1
1
I
- 1)I
1
= 16 and
1
= 64µA
= 4µA
2
2
2
, the
I
2
are
BE
. If