EVB-EMC1002/EMC1033 User Manual

3 Circuit Description

3.1Introduction

The EMC1002 EVB provides the means to demonstrate EMC1002/1033 features and to view and modify registers. LED Indicators and test points are included to show status information and a fan driver circuit linearly drives a 5V fan to 3 different speeds based on programmable temperature limits.

3.2EMC1002/1033

The EMC1002 is an SMBus temperature sensor with 1 internal and 1 external sensor in an 8 pin MSOP package. The EMC1033 has the same features plus support for a second external sensor in parallel with Remote 1 using the “Anti-Parallel Diode” (APD) function. Communications with the EMC1002/1033 is via the SMBus. Alert/Therm2 and Addr/Therm outputs may be configured to assert when temperatures exceed programmed limits.

3.3USB to SMBus Bridge

The USB to SMBus bridge is based on an 8051 microcontroller with integrated USB and SMBus interfaces as well as internal flash and RAM. During EVB manufacture, firmware is loaded into the bridge that provides the interface between the SMBus and the USB driver. Power is sourced to the MCU from the USB interface.

3.4Remote Diode with Resistance Error Correction (R.E.C.)

Two diode-connected 2N3904 transistors may be mounted on the EVB, Remote1 and Remote2. Remote2 is only populated for the EMC1033 EVB and may be disabled by removing jumpers on JP1. The Remote1 diode DN signal path has a series resistor to demonstrate the EMC1002/1033’s R.E.C. feature. The resistor may be effectively removed from the circuit by installing a jumper on JP1. See the Jumper Settings and Connection List for details on jumper settings.

3.5Power Source

This demo board derives +5V power from the USB port. The bridge microcontroller has an internal voltage regulator that supplies +3.3V to the EMC1002/1033 and other EVB circuits.

3.6Fan Drive Circuit

The fan drive circuit linearly drives a 5V, 2-wire fan. Three different drive voltages are possible with the resistor values used on this EVB, 0, 2.4 and 4.1V. If R6 is populated with an 820 ohm resistor, the fan drive voltages will be approximately 2.4, 3.2. and 4.1V. Other fan drive voltage combinations can be achieved by varying R3, R4 and R6. R3 and R4 are located on the top side of the PCB next to transistor Q1. R6 is on the bottom side of the PCB directly opposite Q1.

Note: Full fan ON cannot be achieved with this circuit due to transistor voltage drop.

The fan drive voltage is set by controlling Q1’s base and emitter voltages. When neither the Alert/Therm2 or Addr/Therm outputs are asserted low, no current flows through Q1’s base terminal so the base and emitter voltages are high and the fan will be OFF. When the Alert/Therm2 output is asserted low, the base voltage is set by the resistor divider R3/R4. When the Addr/Therm output is asserted low, the transistor is turned ON fully, resulting in the maximum fan drive voltage for this circuit, which is approximately 4.1V.

3.7System Interrupts / LEDs

The Alert/Therm2 and Therm outputs each have a dual-color LED to indicate the Normal (green) and Alert (red) status The Alert/Therm2 line is also routed to the USB bridge to provide Alert status to the RegMan application.

SMSC EMC1002/EMC1033

Revision 1.1 (12-14-06)

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