Rainbow Electronics MAX6632 - Manual (Page 5)

MAX6629–MAX6632
12-Bit + Sign Digital Temperature Sensors
with Serial Interface
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Detailed Description
The MAX6629–MAX6632 are local digital temperature
sensors with a serial bus. The MAX6629–MAX6632 are
typically interfaced to a µC in temperature sensing and
control applications. The MAX6629–MAX6632 convert
temperature to a 12-bit + sign word with a 0.0625°C
LSB. The data is communicated through a simple serial
interface with a
CS (Chip Select) line, SO (Data) line,
and SCK (Clock) line. This interface can be directly
connected to, and is fully compatible with, SPI inter-
faces. This interface can also be connected to virtually
any processor, which has at least three general-pur-
pose input/output (GPIO) lines available to implement
software “bit banging.”
The high resolution of the MAX6629–MAX6632 makes
them especially useful in thermal control loops, HVAC
systems, or in any system where quick anticipation of
temperature trends is useful. The MAX6629–MAX6632
can produce temperature data in excess of +150°C,
although they are specified for a maximum operating
temperature of +150°C. This extended temperature
range especially makes it useful in automotive under-
hood applications. The low power consumption is also
ideal in battery-operated and portable applications.
The MAX6631/MAX6632 are optimized for minimum
power consumption with their 8s conversions. The
MAX6629/MAX6630 provide faster conversions, 0.5s, at
the expense of power consumption. The low quiescent
supply current enables the device to be powered from
a logic line or the output of a gate where the high level
exceeds 3V, as shown in Figure 1. While the
MAX6629–MAX6632 are not specifically equipped with
a software shutdown mode, the hardware shutdown
can easily be implemented by setting the gate output to
low. Pulling
CS low without a clock also puts the device
in idle mode. Take care to ensure that the logic output
is not noisy, as excessive noise on V CC can affect tem-
perature measurement accuracy.
ADC Conversion Sequence
The MAX6629–MAX6632 continuously convert temper-
ature to digital data. Setting
CS low stops any conver-
sion in progress, places the device in idle mode, and
makes data available for reading. Setting
CS high starts
a new conversion. CS must remain high for at least 0.3s
to allow for the conversion to be completed. Figure 2
shows the timing relationship between conversion time
and conversion rate.
SPI Digital Interface
The MAX6629–MAX6632 are compatible with SPI seri-
al-interface standards (Figure 3) and are designed to
be read-only devices.
CS’s rising edge always starts a
new conversion and resets the interface.
CS must stay
high for a minimum of 300ms to allow the conversion to
Figure 2. Conversion Time and Rate Relationships
MAX6629
MAX6630
MAX6631
MAX6632
0.25s ADC CONVERSION TIME
MAX6631
MAX6632
CONVERSION PERIOD
8s
MAX6629
MAX6630
CONVERSION PERIOD
0.5s
0.25s ADC CONVERSION TIME
Figure 1. Powering the Sensor from a Logic Gate
LOGIC LINE WHERE V LOGIC > 3V
MAX6629
MAX6630
MAX6631
MAX6632
V CC
SO
GND
SCK
CS