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MAX1298CEAE+

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20
MAX1298/MAX1299
12-Bit Serial-Output Temperature Sensors
with 5-Channel ADC
10 ______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1 AIN1
Analog Input 1. Negative differential input relative to AIN0 or positive differential input relative to AIN5
(Table 5). Connect to the cathode of external diode 1 for remote temperature sensing.
2 SHO
Shield Output. Used to suppress leakage currents at the anodes of remote temperature sensors (see Remote
Diode Shielding). May also be connected to the shield of twisted-pair input cables used for remote
temperature measurements. Leave unconnected for other applications.
3 AIN2
Analog Input 2. Positive differential input relative to AIN3 or positive differential input relative to AIN5
(Table 5). Connect to the anode of external diode 2 for remote temperature sensing.
4 AIN3
Analog Input 3. Negative differential input relative to AIN2 or positive differential input relative to AIN5
(Table 5). Connect to the cathode of external diode 2 for remote temperature sensing.
5 AIN4 Analog input 4. Positive differential input relative to AIN5 (Table 5).
6 GND Ground. Connect to pin 13.
7 SSTRB
Serial Strobe Output. SSTRB goes low at the beginning of an A/D conversion, and it goes high when the
conversion is finished.
8 CS
Active-Low Chip Select. Data will not be clocked into DIN unless CS is low. When CS is high, DOUT is at high
impedance.
9 DOUT Serial Data Output. DOUT transitions on the falling edge of SCLK.
10 DIN Serial Data Input. DIN latches data on the rising edge of SCLK.
11 SCLK Serial Clock Input. Clocks data in and out of the serial interface.
12 V
DD
Positive Supply Voltage. Bypass with a 0.1µF capacitor to GND (pin 13).
13 GND Ground (star ground)
14 REF
Reference-Buffer Output/ADC Reference Input. Reference voltage for A/D conversion. Bypass to GND (pin 13)
with a 0.1µF capacitor. Select reference mode by writing to configuration byte (Table 2).
15 AIN5 Analog Input 5. Negative differential input relative to AIN0–AIN4 (Table 5).
16 AIN0
Analog Input 0. Positive differential input relative to AIN1 or positive differential input relative to AIN5
(Table 5). Connect to the anode of external diode 1 for remote temperature sensing.
MAX1298/MAX1299
Detailed Description
The MAX1298/MAX1299 are low-power, serial-output,
multichannel ADCs with temperature-sensing capability
for thermostatic, process-control, and monitoring appli-
cations. An algorithmic switched-capacitor converter
with T/H circuitry for both positive and negative inputs
supports fully differential 12-bit conversions from an
internal temperature sensor, two external temperature
sensors, or voltage sources in a variety of channel con-
figurations. Microprocessor (µP) control is made easy
through a flexible 3-wire serial interface.
Figure 1 shows a simplified functional diagram of the
internal architecture for the MAX1298/MAX1299. In tem-
perature-sensing mode, the multiplexer (mux) steers
bias currents through internal or external diodes while
the ADC computes their temperature in relation to
changes in forward voltage. Channels not used for tem-
perature measurement can be configured to measure
other system voltages.
12-Bit Serial-Output Temperature Sensors
with 5-Channel ADC
______________________________________________________________________________________________________ 11
INPUT
REGISTER
DIODE
BIAS
CONTROL
CONTROL
LOGIC
INPUT
MUX
OUTPUT
REGISTER
CLOCK
12-BIT
ADC
SHIELD
OUTPUT
T/H
T/H
IN
+
IN
-
V
DD
GND
DOUT
CS
SCLK
DIN
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
V
DD
/4
SHO REF
REF
MAX1298
MAX1299
Figure 1. Functional Diagram
MAX1298/MAX1299
12-Bit Serial-Output Temperature Sensors
with 5-Channel ADC
12 ______________________________________________________________________________________
Converter Operation
Figure 2 shows a simplified model of the converter
input structure. Once initiated, a voltage conversion
requires 64 f
CLK
periods, where f
CLK
is the internal
master clock. Each conversion is preceded by 13 f
CLK
periods of warm-up time, performed in twelve 4 f
CLK
period cycles, and followed by 3 f
CLK
periods to load
the output register. SSTRB falls at the beginning of a
conversion and rises at the end of a conversion.
Inputs IN+ and IN- charge capacitors C
HOLDP
and
C
HOLDN
, respectively, during the acquisition interval
that occurs during the first f
CLK
period of the first con-
version cycle. In the second f
CLK
period, the T/H
switches open so that charge is retained on C
HOLDP
and C
HOLDN
as a sample of the differential voltage
between IN+ and IN-. This charge is transferred to the
ADC during the third and fourth f
CLK
periods.
The reference sampling process begins in the second
conversion cycle and continues until the conversion is
complete. Sampling occurs during the second and
fourth f
CLK
periods to yield an effective doubling of the
reference voltage. The reference sampling requirement
is signal dependent and may or may not occur in every
subsequent conversion cycle.
Temperature conversion is essentially nothing more than
subtracting the results of two sequential voltage conver-
sions. The only difference is that output registers are not
loaded at the end of the first conversion. Thus, tempera-
ture conversions require 2 x 64 - 3 = 125 f
CLK
periods.
Figures 3a and 3b show timing diagrams for voltage
and temperature conversions, respectively.
Track/Hold
The T/H stage for the MAX1298/MAX1299 is a simple
switched-capacitor sampling operation. The time
required for the T/H stage to acquire an input signal is
a function of how fast its input capacitance is charged.
If the signal source impedance is high, the acquisition
time lengthens and more time must be allowed
between conversions. The acquisition time (t
ACQ
) is the
TIMING/CONTROL
LOGIC
FULLY
DIFFERENTIAL
A/D
OUTPUT
GAIN
OF 2
IN+
IN-
REF
TRACK AND HOLD
C
HOLDP
4pF
C
HOLDN
4pF
C
REF
4pF
R
R
30kΩ
R
IN
40kΩ
R
IN
40kΩ
T/H
T/H
Figure 2. Converter Input Structure
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20

MAX1298CEAE+

Mfr. #:
Buy MAX1298CEAE+
Manufacturer:
Maxim Integrated
Description:
Board Mount Temperature Sensors 12-Bit Serial-Output w/5Ch ADC
Lifecycle:
New from this manufacturer.
Delivery:
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