Rainbow Electronics LM88 - Manual (Page 5)

1.0 Functional Description
1.1 PIN DESCRIPTIONS
V + This is the positive supply voltage pin, which has
a range of 2.8 to 3.8 volts. This pin should be
bypassed with a 0.1µF capacitor to ground.
GND This is the ground pin.
D0+, D1+ These pins connect to the positive terminal of the
diodes (e.g. a 2N3904 collector base shorted or a
Pentium thermal diode anode) and provide the
source current for forward biasing the diodes for
the temperature measurement. During a tem-
perature conversion, the current source switches
between 120µA and 12µA. The diodes are
sampled sequentially.
D− This pin should be connected to the negative pin
of each diode (e.g. a 2N3904 emitter or a Pen-
tium thermal diode cathode). A star connection is
recommended. Separate traces should be routed
from this pin to each diode cathode. This pin
biases the negative diode terminals to approxi-
mately 0.7V.
O_CRIT This is an active-low open-drain digital output. It
goes LOW when a comparison of either diode
temperature reading to the setpoint T_CRIT is
true. It returns to HIGH when the comparison of
the diode temperature, that caused the true con-
dition, to T_CRIT ± 1˚C is false. The CRIT com-
parator can be factory programmed to make a
greater than or less than comparison. (See Sec-
tion 1.3 LM88 OPTIONS)
O_SP1 This is an active-low open-drain digital output. It
goes LOW when the comparison of the tempera-
ture reading of diode one to the value of T_SP1 is
true. The SP1 comparator has a built in hyster-
esis of 1˚C. Therefore, O_SP1 returns to HIGH
when diode one’s temperature comparison to the
value of T_SP1
± 1˚C is false. The SP1 compara-
tor can be factory programmed to make a greater
than or less than comparison.(See Section 1.3
LM88 OPTIONS)
O_SP0 This is an active-low open-drain digital output. It
goes LOW when the comparison of the tempera-
ture reading of diode one to the value of T_SP0 is
true. The SP0 comparator has a built in hyster-
esis of 1˚C. Therefore, O_SP0 returns to HIGH
when diode one’s temperature comparison to the
value of T_SP0
± 1˚C is false. The SP0 compara-
tor can be factory programmed to make a greater
than or less than comparison.(See Section 1.3
LM88 OPTIONS)
10132611
a) When programmed for a greater than comparison
10132612
b) When programmed for a less than comparison
FIGURE 2. Comparator output temperature response diagrams
LM88
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