Rainbow Electronics MAX1617A User Manual
Page 13
successful read of the status byte, unless the fault per-
sists. Note that the ALERT interrupt latch is not auto-
matically cleared when the status flag bit is cleared.
When auto-converting, if the T
HIGH
and T
LOW
limits are
close together, it’s possible for both high-temp and low-
temp status bits to be set, depending on the amount of
time between status read operations (especially when
converting at the fastest rate). In these circumstances,
it’s best not to rely on the status bits to indicate rever-
sals in long-term temperature changes and instead use
a current temperature reading to establish the trend
direction.
Conversion Rate Byte
The conversion rate register (Table 7) programs the time
interval between conversions in free-running auto-convert
mode. This variable rate control reduces the supply cur-
rent in portable-equipment applications. The conversion
rate byte’s POR state is 02h (0.25Hz). The MAX1617A
looks only at the 3 LSB bits of this register, so the upper 5
bits are “don’t care” bits, which should be set to zero. The
conversion rate tolerance is ±25% at any rate setting.
Valid A/D conversion results for both channels are avail-
able one total conversion time (125ms nominal, 156ms
maximum) after initiating a conversion, whether conver-
sion is initiated via the RUN/STOP bit, hardware STBY
pin, one-shot command, or initial power-up. Changing the
conversion rate can also affect the delay until new results
are available (Table 8).
Manufacturer and Device ID Codes
Two ROM registers provide manufacturer and device ID
codes (Table 4). Reading the manufacturer ID returns
4Dh, which is the ASCII code “M” (for Maxim). Reading
the device ID returns 01h, indicating a MAX1617A
device. If READ WORD 16-bit SMBus protocol is
employed (rather than the 8-bit READ BYTE), the least
significant byte contains the data and the most signifi-
cant byte contains 00h in both cases.
Slave Addresses
The MAX1617A appears to the SMBus as one device
having a common address for both ADC channels. The
device address can be set to one of nine different val-
ues by pin-strapping ADD0 and ADD1 so that more
than one MAX1617A can reside on the same bus with-
out address conflicts (Table 9).
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
______________________________________________________________________________________
13
RUN/
STOP
6
0
0
POR
STATE
Standby mode control
bit. If high, the device
immediately stops con-
verting and enters stand-
by mode. If low, the
device converts in either
one-shot or timer mode.
Masks all ALERT inter-
rupts when high.
FUNCTION
RFU
5–0
0
Reserved for future use
MASK
7 (MSB)
BIT
NAME
Table 5. Configuration-Byte Bit
Assignments
Table 7. Conversion-Rate Control Byte
Table 6. Status-Byte Bit Assignments
*
These flags stay high until cleared by POR, or until the status
byte register is read.
LHIGH*
6
A high indicates that the local high-
temperature alarm has activated.
A high indicates that the ADC is busy
converting.
FUNCTION
LLOW*
5
A high indicates that the local low-
temperature alarm has activated.
RHIGH*
4
A high indicates that the remote high-
temperature alarm has activated.
RLOW*
3
A high indicates that the remote low-
temperature alarm has activated.
OPEN*
2
A high indicates a remote-diode conti-
nuity (open-circuit) fault.
RFU
1
BUSY
7
(MSB)
Reserved for future use (returns 0)
RFU
0
(LSB)
Reserved for future use (returns 0)
BIT
NAME
0.125
01h
33
30
0.25
02h
35
0.5
03h
48
1
04h
70
2
05h
128
4
06h
0.0625
00h
225
8
07h
425
RFU
08h to
FFh
—
DATA
CONVERSION
RATE
(Hz)
AVERAGE SUPPLY
CURRENT
(µA typ, at V
CC
= 3.3V)