DS1780

2 of 28

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

SIGNAL

DIRECTION

DESCRIPTION

Digital I/O

The lowest order programmable bit of the 2-wire bus address. This pin

functions as an output when doing a NAND TREE test.

2

A1

Digital Input

The highest order programmable bit of the 2-wire bus address.

3

SDA

Digital I/O

2-wire bus bi-directional data. Open-drain output.

4

SCL

Digital Input

2-wire bus synchronous clock.

5

FAN1

Digital Input

6

FAN2

Digital Input

7

CHS

Digital I/O

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.

8

GNDD

GROUND

Internally connected to all digital circuitry.

POWER

(Electrolytic or Tantalum) and 0.1 µF (ceramic) bypass capacitors.

10

INT

Digital Output

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.

11

Digital Input/

Analog Output

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.

12

RST

Digital I/O

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.

13

GNDA

GROUND

Internally connected to all analog circuitry. The ground reference for all

analog inputs.

14

Analog Input

on this pin from 0V to 3.6V. An external resistor ladder is required for

monitoring a -12V supply (see Figure 1).

15-19

Analog Inputs

A/D inputs for 5 positive voltages.

20-24

VIDx

Digital Inputs

Voltage supply readouts from the processor. These values are read in the VID

and VID4 Status Registers.