LM87
Pin Description
Pin
Name(s)
GND
(Continued)
Number
of Pins
1
Type
GROUND
Description
The system ground pin. Internally connected to all circuitry. The
ground reference for all analog inputs and the DAC output. This pin
needs to be connected to a low noise analog ground plane for
optimum performance of the DAC output.
+3.3 V V
+
power. Bypass with the parallel combination of 10 µF
(electrolytic or tantalum) and 0.1 µF (ceramic) bypass capacitors.
Interrupt active low open-drain output. This output is enabled when
Bit 1 in the Configuration Register is set to 1. The default state is
disabled. It has an on-chip 100 kΩ pullup resistor. Alternately used
as an active low output to signal SMBus Alert Response Protocol.
0 V to +2.5 V amplitude 8-bit DAC output. When forced high on
power up by an external voltage the NAND Tree Test mode is
enabled which provides board-level connectivity testing.
Master Reset, 5 mA driver (open-drain), active low output with a 20
ms minimum pulse width. Available when enabled via Bit 4 in the
Configuration register. It also acts as an active low power on
RESET input. It has an on-chip 100 kΩ pullup resistor.
Analog input for monitoring the cathode of the first external
temperature sensing diode.
Analog input for monitoring the anode of the first external
temperature sensing diode.
Analog input for monitoring +12 V.
Analog input for monitoring +5 V.
Digitally programmable analog input for monitoring Vccp2 (0 to 3.6
V input range) or the cathode of the second external temperature
sensing diode.
Digitally programmable analog input for monitoring +2.5 V or the
anode of the second external temperature sensing diode.
Analog input (0 to 3.6 V input range) for monitoring Vccp1, the core
voltage of processore 1.
Digitally programmable dual function digital inputs. Can be
programmed to monitor the VID pins of the Pentium/PRO and
Pentium II processors, that indicate the operating voltage of the
processor, or as interrupt inputs. The values are read in the
VID/Fan Divisor Register and the VID4 Register. These inputs have
on-chip 100 kΩ pullup resistors.
Pin
Number
8
V
+
(+2.8 V to
+3.8 V)
INT# /ALERT#
9
10
1
1
POWER
Digital Output
DACOut/NTEST_IN
11
1
Analog
Output/Digital
Input
Digital I/O
RESET#
12
1
D1−
D1+
+12Vin
+5Vin
Vccp2/D2−
13
14
15
16
17
1
1
1
1
1
Analog Input
Analog Input
Analog Input
Analog Input
Analog Input
+2.5Vin/D2+
Vccp1
VID4/IRQ4-
VID0/IRQ0
18
19
20-24
1
1
5
Analog Input
Analog Input
Digital Inputs
TOTAL PINS
24
#
Indicates Active Low (“Not”)
3
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
