Rainbow Electronics MAX6628 - Manual (Page 5)

MAX6627/MAX6628
Remote ±1°C Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface
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Detailed Description
The MAX6627/MAX6628 remote digital thermometers
report the temperature of a remote sensor. The remote
sensor is a diode-connected transistor—typically, a
low-cost, easily mounted 2N3904 NPN type—that
replaces conventional thermistors or thermocouples.
The MAX6627/MAX6628 can also measure the die tem-
perature of other ICs, such as µPs or µCs, that contain
an on-chip, diode-connected transistor.
Remote accuracy is ±1°C when the temperature of the
remote diode is between 0°C and +125°C and the tem-
perature of the MAX6627/MAX6628 is +30°C. Data is
available as a 12-bit + sign word with 0.0625°C resolu-
tion. The operating range of the device extends from
-55°C to +125°C, although the architecture of the
device is capable of interpreting data up to +145°C.
The device itself should never exceed +125°C.
The MAX6627/MAX6628 are designed to work in con-
junction with an external µC or other intelligent device
serving as the master in thermostatic, process-control,
or monitoring applications. The µC is typically a power
management or keyboard controller, generating SPI
serial commands by “bit-banging” GPIO pins.
Two conversion rates are available; the MAX6627 con-
tinuously converts data every 0.5s, and the MAX6628
continuously converts data every 8s. Either device can
be read at any time and provide the data from the last
conversion. The slower version provides minimal power
consumption under all operating conditions. Or, by tak-
ing CS low, any conversion in progress is stopped, and
the rising edge of CS always starts a fresh conversion
and resets the interface. This permits triggering a con-
version at any time so that the power consumption of
the MAX6627 can be overcome, if needed. Both
devices operate with input voltages between +3.0V and
+5.5V and are specified between -55°C and +125°C.
The MAX6627 and MAX6628 come in space-saving 8-
pin SOT23 packages.
ADC Conversion Sequence
The device powers up as a free-running data converter
(Figure 1). The CS pin can be used for conversion con-
trol. The rising edge of CS resets the interface and
starts a conversion. The falling edge of CS stops any
conversion in progress, overriding the latency of the
part. Temperature data from the previous completed
conversion is available for read (Tables 1 and 2). It is
required to maintain CS high for a minimum of 320ms
to complete a conversion.
Idle Mode
Pull CS low to enter idle mode. In idle mode, the ADC is
not converting. The serial interface is still active and
temperature data from the last completed conversion
can still be read.
Power-On Reset
The POR supply voltage of the MAX6627/MAX6628 is
typically 1.6V. Below this supply voltage, the interface
is inactive and the data register is set to the POR state,
Figure 1. Free-Running Conversion Time and Rate Relationships
MAX6627
MAX6628
0.5s
SAMPLE
RATE
8s
SAMPLE
RATE 0.25s
CONVERSION
TIME
ADC CONVERTING
ADC IDLE
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
Sign
MSB
Data LSB
Data
Low High-Z High-Z
Table 1. Data Output Format