MX844 查看數據表（PDF） - IXYS CORPORATION
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MX844 Datasheet PDF : 21 Pages
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MX844
IXYS
APPLICATION OPERATING MODE
At the end of the power-on reset period, pin CS is sensed to determine the operating mode. Placing an
external resistor to VCC on pin CS will cause the MX844 to enter the slave mode. In this mode the
synchronous serial I/O port can be connected to a companion microcontroller for full control of the MX844
from the microcontroller.
If a resistor to GND is connected to CS, then the MX844 enters the master mode at power-up and fetches
commands from a 93C46 serial EEPROM operating in the 64 by 16 mode. In this mode, the MX844
operates as the master and sends clock, data, and select to the EEPROM and reads back the EEPROM
data. This mode is useful when the MX844 operates as a stand-alone data acquisition system with a
fixed pattern of measurement scanning. To facilitate electrically isolated measurements the data can be
sent to a computer's serial port using only one wire connected through a single opto-isolator.
If, neither an EEPROM or microcontroller are connected to the MX844, and CS is connected to VCC,
operation defaults to that of all zeroes in the control register (ADC clock = input clock / 8, input channel
IN1, +/- 50mV range). The asynchronous data output has a valid stream of measurement information.
FUNCTIONAL DESCRIPTION
Voltage Regulator
There are three methods of powering the MX844.
1) An external 4.5 to 5.5V supply is connected to VCC, VCC2, and VIN. Pins DRV and RIN are no-
connect or connected together.
2) VIN is connected to a 6 to 40V supply. DRV is connected to RIN, thus utilizing the internal pass
element.
3) VIN is connected to a 6 to 40V supply. An external PNP transistor such as the MMBTA56 or BCX53 is
used for the pass element. The PNP transistor's emitter, base, and collector are connected to pins
VIN, DRV, VCC respectively. RIN must be connected to VIN.
Power-On Reset
The MX844 contains a power-on reset circuit that resets all the internal flip-flops and initializes the
internal registers to zero. The reset circuit will also generate a reset condition if the voltage at pin VCC
drops to approximately 3.8V.
Oscillator
The oscillator configuration consists of a crystal/resonator connected between pins X1 and X2 and a
capacitor to GND on both pins. The capacitor value depends on the crystal/resonator but is usually
between 15 and 27pF. Alternatively, an external clock may be input to pin X1, with X2 floating. Nominal
DC self-bias at pin X1 is 800mV. In either case the clock is internally AC coupled, therefore clock rates
below 100KHz are not recommended.
Temperature Sensor
The internal temperature sensor is selected for measurement by setting the control register bits for a full
scale of +/-250mV and setting the unipolar bit. The temperature value read from the ADC consists of an
offset value plus the slope. To convert to a standard temperature scale it is necessary to subtract the
constant offset and then multiply by a constant that matches the standard scale desired.
Self-heating of the internal temperature sensor will occur due to the device power dissipation. The
maximum heating will occur when the internal pass element is used in conjunction with a high supply
voltage.
MX844
Drawing No. 084423
4
08/25/06
www.claremicronix.com
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