DS1780 Datasheet, PDF (2/28 Pages) Dallas Semiconductor – CPU Peripheral Monitor

DS1780
DESCRIPTION
The DS1780 is a highly integrated system instrumentation monitor ideal for use in personal computers, or
any microprocessor-based system. It monitors ambient temperature, six power supply voltages, and the
speed of two fans. Fan speed can also be controlled with the use of an internal 8-bit DAC. All
measurements are internally converted to a digital format for easy processing by the CPU.
The DS1780 can be reset to its default power-up state via a remote reset function with internal debounce
and delay. It features an interrupt that can be programmed to become active should any of the functions
the DS1780 is monitoring fall out of spec.
For board-level testability, an internal NAND TREE function simplifies the system design. A chassis
intrusion input is featured to enhance system security.
Programming and data readout are accessed via a simple 2-wire interface with 2-bit addressability. The
DS1780 power supply range of 2.8V to 5.75V allows for monitoring of parameters for 3V or 5V systems.
The DS1780 is assembled in a compact 173-mil TSSOP package.
Detailed Pin Description Table 1
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15-19
20-24
SIGNAL
A0/NT_OUT
A1
SDA
SCL
FAN1
FAN2
CHS
GNDD
V_DD
INT
V_OUT/NT_IN
RST
GNDA
+2.5V_S/+V_CCP2
+xxV_IN
VIDx
DIRECTION
Digital I/O
Digital Input
Digital I/O
Digital Input
Digital Input
Digital Input
Digital I/O
GROUND
POWER
Digital Output
Digital Input/
Analog Output
Digital I/O
GROUND
Analog Input
Analog Inputs
Digital Inputs
DESCRIPTION
The lowest order programmable bit of the 2-wire bus address. This pin
functions as an output when doing a NAND TREE test.
The highest order programmable bit of the 2-wire bus address.
2-wire bus bi-directional data. Open-drain output.
2-wire bus synchronous clock.
0 to V_DD amplitude fan tachometer input.
0 to V_DD amplitude fan tachometer input.
An active high input from an external circuit, which latches a Chassis
Intrusion event. This line can go high without any clamping action regardless
of the powered state of the DS1780. The DS1780 provides an internal open
drain on this line, controlled by Bit 6 of Configuration Register, to provide a
minimum 20 ms reset of this signal.
Internally connected to all digital circuitry.
+3.3V or +5V V_DD power. Bypass with the parallel combination of 10 µF
(Electrolytic or Tantalum) and 0.1 µF (ceramic) bypass capacitors.
Active-low Programmable interrupt output. The output is enabled when Bit 1
of the Configuration Register is set to 1. The default state is disabled.
An active-high input that enables NAND Tree board-level connectivity
testing. Refer to “NAND Tree Testing” Section. Used as DAC output when
NAND Tree is not selected.
Master Reset, 5 mA open drain driver, active low output with at least a 20 ms
minimum pulse width. Available when enabled via Bit 4 in Configuration
Register. This is a bi-directional I/O pin. It acts as power on RESET input.
Internally connected to all analog circuitry. The ground reference for all
analog inputs.
Analog input for monitoring -12V or +V_CCP2. DS1780 will measure voltages
on this pin from 0V to 3.6V. An external resistor ladder is required for
monitoring a -12V supply (see Figure 1).
A/D inputs for 5 positive voltages.
Voltage supply readouts from the processor. These values are read in the VID
and VID4 Status Registers.
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