Systems based on MAX6636 multi-point temperature monitoring

Introduction

MAX6636 is a multi channel of precision temperature monitors, not only to monitor local temperature and external can add up to 6 a diode.

Each channel has programmable low temperature alarm, 1, 4, 5 and 6 channel also features programmable high temperature alarm. When a channel measured temperature reaches the pre-set limit value, the State Register of the corresponding bit is set. The most significant advantages of MAX6636 is a miniature 20-pin TSSOP package, to be able to monitor the CPU and other 4 location of temperature, mainly used in desktop computers, notebooks, workstations, and servers.

1 MAX6636 package and performance characteristics

1.1 pin function

MAX6636 pins diagram shown in Figure 1.

MAX6636 the PIN function is as follows: DXPl ~ DXP6: Remote temperature sensor is end. When not used to remote diode, the feet are blank or connect to V ¡ø PIN. DXN at DXP and should be connected between a 2 200 pF capacitor filter out the noise. DXNl ~ DXN6: Remote temperature sensor of the negative side. The PIN is connected internally to the ground. STBY: standby mode input pin, low level valid. At this point temperature values and threshold value is preserved. NC: empty feet. In the application circuit, the PIN must be connected to ground. OVERT: open-drain output. Practice, when 1, 4, 5, 6-channel in a temperature value beyond its pre-set programmable over temperature threshold, can be used to slow down or turn off the fan, as well as control the CPU clock. VCC: power input. Use O. 1 μ F capacitor bypass to the ground. ALERT: open-drain output. Used as interrupt or SMBus (System management bus) alerts. SMBDATA: SMBus serial data input/output. Need to add a pull-up resistor. SMBCLK: SMBus serial clock input. Need to add a pull-up resistor. GND: power to the client.

1.2 performance characteristics

MAX6636 's main function characteristics are as follows:

6 channel thermal diode input; local temperature sensor; + 60 ° c to + 100 ° c range distance measuring accuracy of 1 ° c; the temperature monitoring begins in POR failure to protect the security system; OVERT and ALERT output for outages, slow down or off; for hardware downtime STBY input mode; the small 20-pin TSSOP Package; 2-wire SMBus interface.

2 works

MAX6636 to monitor its own temperature as well as external up to six diodes connected temperature of transistors.

All temperature channel has programmable alarm threshold, channel 1, 4, 5 and 6 also features programmable over temperature threshold. When a channel measured temperature exceeded their respective threshold, the State Register of State location. 2 open-drain output OVERT and ALERT based on status register of these bits into a low level.

Its 2-wire serial interface supports standard SMBus Protocol: write Byte, send byte read bytes, and the bytes received to complete the reading of the temperature data and alarm threshold programming.

MAX6636 normal working hours, on-chip A/D converter to work properly.

Analog Input multiplexer selection on-chip temperature sensor for measuring the local temperature, or select the remote temperature sensor to measure distance. These signals are ADC digitization, the results into a local or remote temperature value registers.

2.1 temperature data format

MAX6636 chip ADC minimum bit corresponds O.125 ℃, the ADC can range from 0 ° c ~ 127.875 ° c, the temperature data format and extended temperature resolution as table 1 and table 2.

2.2 MAX6636 registers

MAX6636 registers are used to store the results of remote and local temperature, extreme high and low temperature, and setting and control devices.

(1) local temperature registers

Local temperature registers address 07H, POR status is 00 through SMBus bus read local temperature value.

(2) remote temperature registers

MAX6636 six remote temperature registers, 01H ~ 06H, read through the SMBus bus corresponding channel remote temperature value.

(3) structure of register

MAX6636 3 structure of the register.

Structure of register l using the 5-bit: bit 7 is standby mode control bits, 1 stop is MAX6636 conversion in standby mode; bit 6 is reset, reset the device reset 1; bit 5 is temporarily enable bit, reset O the SMBus bus enters the suspended state; bit 4 is the channel 1. shaan speed conversion, high effective; bit 3 is resistance canceling, 1 cancel channel 1 and thermal diode series resistance, resistance range is O ~ 100 Ω.

Structure of register 2 use the 7-bit: bit 6 is a local alarm mask bit, 1 channel is shielding off local alarm signal; bit 5-bit 0 is the remote channel masks alarm interrupt output, high level valid.

Structure of register 3 with the 4-bit: bit 5, 4, 3, O are channel 6, 5, 4, 1 over-temperature alarm Maskable Interrupt, high level valid.

(4) status register

MAX6636 also has three State registers.

/P>

Status register 1 describes the local temperature or high temperature alert measurement temperature remotely, if the local temperature or remote measurement of temperature is higher than ALERT registers set temperature threshold value, then the corresponding bit is reset to 1.

Status register 2 describes the remote measurement of channel 1, 4, 5, 6, over-temperature alarm in temperature.

If the four-channel remote measurement of temperature is higher than 0VERT registers set over temperature threshold value, then the corresponding position 1.

Status register 3 describes the remote sensing diode fault, if the remote measurement channel sensor to diode open circuit or short circuit, then the corresponding bit is reset to 1.

(5) limit register

MAX6636 11 limit registers, including 1 local high temperature alarm limit register, 6 remote high-temperature alarm limit registers and 4 remote over temperature limit registers.

These registers can be read/write via SMBus.

2.3 serial bus interface

MAX6636 as from devices connected to the serial bus, from the master device of the control.

Note: remote measurement channel 1 with 11 data bits, least significant bit is + O.125 ℃; while other channel provides eight data bits, least significant bit is + 1 ° c. 8 most important data from local or remote read temperature registers, remote measurement channels of the other three bits can be read from the extended temperature registers.

2.4 device addressing

In General, each SMBus devices have a 7-bit address (except some extended address for 10-bit).

When the main devices across the bus makes a device address when you have the address of the device will respond. The address is 4D MAX6636 (1001101).

2.5 ALERT alarm response address

SMBus interrupt alarm response pointing to those simple device provides a fast, default confirmation.

For those who lack of complex logic for devices, you need to connect through a hub. An interrupt signal is received, the host will issue an interrupt source address, the address of the device will respond.

ALERT signal can respond to many different devices, this response similar to the I2C bus.

If more than one device ALERT waiting to be responding, according to the agreement, you have the SMBus minimum bit address of the device takes precedence. Once the warning response MAX6636 response address, as long as the output of the error caused by ALERT status does not exist, it will reset ALERT output. If the SMBus ALERT remains on a low level, primary device will once again send an interrupt request until all ALERT signal devices are low.

2.6 OVERT over-temperature alarm

MAX6636 4 remote over temperature limit registers to store remote alarm output limit values.

When the measured temperature value of a channel than it limiting values of the register storage, OVERT will render the alarm status and the status will remain until its measured value drops to its set value of 4 degrees centigrade. This over-temperature alarm output can be used for the cooling system of the excitation source, initialize the clock source, or as a system to automatically shutdown trigger switch to avoid the machine because the heat losses.

2.7 sensor fault detection

DXP input, MAX6636 have a detectable external sensor diode is open circuit fault detectors.

This is a simple voltage comparator, DXP voltage exceeding (VCC a 1V) is triggered. If you trigger the conversion begins to detect failure to check the comparator output and sets the status register 3 for 1-bit ~ 6 bits. For example, because the diode shorted, ADC outputs 128 (1111 1111). Because the device working properly extended to + 127 ° c, no such output values, so it is an error state.

MAX6636 about 4 ms detection if a diode failure, once detected failure, will follow the conversion order next channel probe.

Short circuit diode may cause alarm interrupt production, so the unused channel pin should not be connected.

3 application

3.1 application circuit

Typical application circuit MAX6636 as shown in Figure 2, a shield of twisted-pair cable with a separation of transistors.

SMBCLK, SMBDATA, ALERT and OVERT required through 4.7 electrical block k Ω to VCC, SMBCLK and SMBDATA can directly and I/0 controller (such as Intel 820) is connected to the SMBus.

ALERT received controller interrupt input. OVERT General and fan control circuit is connected, when the corresponding interrupt response, the port accordingly slow down or turn off the action.

The precision of the factors affecting 3.2

3.2.1 remote sensing diodes

MAX6636 and embedded in the substrate in the CPU or discrete Transistor transistor work together.

Where the substrate is PNP-transistor in General, the collecting electrode attached to the substrate. Discrete transistor PNP or NPN can be connected into a diode-type (base and collector shorted). If you use the NPN tube, collector and base connection to DXP, emitter connected to the DXN; if you use the PNP tube, the collector and base connected to the DXN, DXP emitter connected to. A lot CPU with substrate transistor, in order to reduce their changes brought about by the error, you need to consider the following factors:

① n transistor's ideal factor.

Remote loggingTemperature accuracy depends primarily on remote sensing diodes ideal factor n, MAX6636 design ideal factor 1.015 nN. For the actual temperature is TA, ideal factor n of sensing diodes, measurement temperature is:

If the application in an ideal factor MAX6636 1.002 CPU, assuming that the sensing diode not received series resistance, so the actual temperature is

For the actual temperature + 85 ° c, measure the temperature of about + 83.91 ℃, error about a 1.09 ℃.

② When the sensor is discrete transistor, the collector and base must be connected together.

This small signal transistor must be and have relatively high forward voltage, or A/D input voltage range will be affected. The ideal temperature, the forward voltage of the maximum value should be greater than 0.25 V/10 A μ, minimum value should be less than 100 μ O.95 V/A, so the application cannot use a high-power transistors. In addition, you should make sure that the base of the resistance is less than 100 Ω.

3.2.2 heat thermal inertia and self-

Accuracy depends not only on remote sensing diodes and internal temperature sensor of temperature, and other factors.

When measuring the local temperature MAX6636, wire to PCB components and templates provide a good thermal contact. When you use the on-chip sensor to measure a CPU or other IC temperature, thermal inertia effects on his practice and, in a transition period, the measurement of the temperature values are close to actual value. When separation distance measuring temperature, transistor SOT 23 or SC a 70 this small package devices will get the best thermal response time. In the heat source and sensor shall be carefully consider thermal gradient, make sure to around through the sensor package air currents do not affect the measuring accuracy. To a considerable extent, since the heat does not affect the measurement accuracy, the remote sensor of self-heating depends on diode current, is negligible.

3.3 PCB routing considerations

Digital circuit boards often are electrical noise environments, while MAX6636 from remote temperature sensor for measuring the voltage is very small, so you must take steps to ensure that the sensor input sensitivity to minimize noise.

In order to reduce the remote temperature measurement error, we recommend that you follow the following route:

① will put away as much as possible MAX6636 remote sensing diodes recently.

If there is no noise source (such as clock generators, data/address bus and CRT), the distance preferably 10.2 ~ 20.4cm.

② when routing, do not use a DXP and DXN signal cable near CRT related pads, and do not use routing path selection in high speed digital signal area.

③ D X P and DXN placed parallel and close to each other.

Since PCB leakage current, if DXP through 20 M Ω to add to the path, it will generate the temperature of + 1 ° c. Therefore, when routing best DXP and set the ground on both sides of the DXN, if possible in the production line consists of a ground level.

④ to minimize possible effects of copper thermocouples and solder joint.

In copper and solder joint office, make sure that the path with the DXP and DXN, with temperature, thermocouple effect is negligible.

⑤ with wide lead to decrease the induction, noise reduction, line width and line spacing is 10 best nail (mil for the non-SI units, 1000 mil = "25" .4 mm).

Conclusion

Multichannel temperature monitors MAX6636 most notable characteristic is the use of miniature 20-pin TSSOP package, can be widely used on the chip size have strict requirements of occasions.

MAX6636 will appear in the notebook and monitor next-generation CPU and has good prospects.