IXYS
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MX844
12 BIT, MULTI-CHANNEL POWER & TEMP
SENSOR FOR MONITOR & CONTROL SYSTEMS
Description:
The MX844 is a fully integrated subsystem that
measures temperature plus differential current and
voltage. An internal temperature sensor measures
ambient temperature with 2.5°C accuracy. Current
and voltage measurements are made differentially
through a four input multiplexer connected to a
programmable gain fully differential sense amplifier.
The differential sense amplifier is optimized to
measure very small positive or negative voltages
near ground for low side bi-directional sensing. A
dual slope ADC converts the temperature sensor or
sense amplifier outputs to a 12-bit digital word that
includes 3 ½ digits plus sign. The input multiplexer
channel and programmable gain amplifier range may
be changed between ADC conversions. An on-chip
voltage regulator enables the MX844 to operate over
a wide input voltage range of 4.5 to 40 volts.
Controller interrupt or over-voltage/over-current
signals may be generated by a pair of 12-bit digital
comparators configured as a window comparator or
simple threshold detection function. The serial port
supports standard 4-wire synchronous serial data, or
asynchronous serial “talk-only” data, and is
compatible with most 3.3V and 5V microcontrollers.
Wide Input Supply Range: 4.5V to 40V
Programmable gain differential amplifier
(±10mV, ±25mV, ±50mV, ±250mV ranges)
4 channel differential input multiplexer
(3 input channels plus ground)
Integrated 12-bit ADC
Serial data output (SDO) with data ready pin
Fine calibration of Full Scale Range (FSR)
using VTRIM pin
Bi-directional Current Sense
Internal temperature sensor with 0.2°C
resolution
Compatible with 3.3V and 5V
Microcontrollers
Operating Temperature Range: -40°C to
85°C
5mm x 5mm, QFN-28 RoHS Package
Ordering Information
Part No.
Description
MX844R
QFN-28 Tube
MX844RTR QFN-28 Tape & Reel
DRV
RIN
VIN
Regulator
IN1P
IN2P
IN3P
VCC
Qty
73
2500
BUF
CAZ
CINT
IZ
Registers
ADC
Control
Serial
I/O
IN1N
IN2N
IN3N
GND
VTRIM
Tem perature
Sensor
Divider
M1
SDI
SDO
SCK
CS
AOUT
DRDY
CMP
X1
X2
SYNC
Typical Application:
Charging
system
MX844
Load
MX844
IN
93C46
eeprom
Batt
T
Load
Rectifier
uP
IN
IN
IN
IN
uP
Battery charge/discharge current, voltage, temperature
MX844
Drawing No. 084423
1
Isolated voltage, current, and temperature sensing
08/25/06
www.claremicronix.com
MX844
Absolute Maximum Ratings
(Voltages with respect to GND=0V)
Parameter
VIN, RIN, DRV
All Other Pins
Storage Temperature
Operating Ambient Temp
Operating Junction Temp
Thermal Resistance
(Junction to Ambient)
ESD Warning
Symbol
Min
Max
45
6
150
85
100
Unit
V
V
C
o
C
o
C
o
C
o
/W
IXYS
T
STG
T
A
T
J
R
θJA
-55
-40
Absolute Maximum Ratings are
stress ratings. Stresses in excess of
these ratings can cause permanent
damage to the device. Functional
operation of the device at these or
any other conditions beyond those
indicated in the operational sections
of this data sheet is not implied.
Exposure of the device to the
absolute maximum ratings for an
extended period may degrade the
device and affect its reliability.
110 Typical
ESD (electrostatic discharge) sensitive device. Although the MX844 features proprietary ESD protection circuitry,
permanent damage may be sustained if subjected to high energy electrostatic discharges. Proper ESD precautions
are recommended to avoid performance degradation or loss of functionality.
DC Electrical Characteristics
Parameter
VCC line regulation
VCC load regulation
VIN supply current
Input bias current
Input bias current offset
Input offset voltage
input common mode
ADC gain error
XTAL = 8MHz, T=25C, Cint = Caz = 10nF, Rint = 68K,
T
A
= +25
o
C
Condition
VIN = 6 to 45V, no external load
VIN = 6V, 15 mA external load
VIN = 6V
selected input channel
differential, input=0, +/-10mV scale
all input channels
+/-250mV range, at 90% input
+/-50mV range
+/-25mV range
+/-10mV range
Min
4.8
4.7
Typ
Max
5.3
4.5
40
4
0.4
300
0.5
0.25
0.25
0.25
Unit
V
V
mA
nA
nA
mV
mV
%
%
%
%
lsb
rms lsb
o
o
3.2
10
-4
-0.4
-300
-0.5
-1.25
-1.5
-1
-3
-2.5
0.2
+/-0.5
1.5
20
ADC linearity
ADC noise
Temperature error
Temperature slope
Temperature offset
Power on reset duration
Digital output low
Digital output high
Digital input low
Digital input high
Digital input current
Clock frequency
Clock input low
Clock input high
Clock input current
MX844
Drawing No. 084423
at half full scale
3
2.5
C
C/lsb
lsb
uS
Zero
o
C
I = 20mA
I = 6mA
VCC-0.5
GND
2
terminal X1
terminal X1
terminal X1
terminal X1
2
3310
100
0.5
0.5
VCC
±1
0.1
GND
2
20
0.4
VCC
50
V
V
V
V
uA
MHz
V
V
uA
08/25/06
www.claremicronix.com
MX844
PIN DESCRIPTION
Pin No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Pin Name
GND
VTRIM
BUF
IZ
CAZ
CINT
IN1P
IN1N
IN2P
IN2N
IN3P
IN3N
M1
SYNC
DRDY
SCK
SDO
SDI
CS
X1
X2
AOUT
CMP
VCC2
VCC
VIN
RIN
DRV
Description
Ground
Optional Full Scale Trim Input
Integrating Resistor Output
Integrator Zero Output
Auto Zero Capacitor Input
Integrator Capacitor Input
Input Channel 1 Positive
Input Channel 1 Negative
Input Channel 2 Positive
Input Channel 2 Negative
Input Channel 3 Positive
Input Channel 3 Negative
Divisor Mode Input
A/D Converter Reset Input
A/D Converter Data Ready Output (Active Low)
Serial Clock Input
Serial Data Output
Serial Data Input
Serial Chip Select (Active Low)
Xtal 1 Input
Xtal 2 Output
Asynchronous Data Output
Comparator Output
Must Be Connected to Vcc
Regulator Output / Logic Supply Input
Regulator Voltage Input
Regulator Internal MOSFET Gate
Regulator External PNP Base Drive
IXYS
MX844
Drawing No. 084423
3
08/25/06
www.claremicronix.com
MX844
APPLICATION OPERATING MODE
IXYS
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
MX844
IXYS
Analog/Digital Converter
Selection of the input channel and the full scale range is accomplished by writing 5 bits in the control
register. An additional 3 bits in the control register in combination with the M1 pin setup the internal clock
dividers. The ADC is a bipolar-input dual slope type with clock period tAD equal to a multiple of the clock
period at pin X1 (tClock). The ADC conversion time consists of 1024 * tAD of auto-zero, 1024 * tAD of
input integration, and 2048 * tAD of reference integration. The result of the analog to digital conversion
can be read using the serial I/O port and is also transmitted on pin AOUT in an asynchronous serial
format. The DRDY pin transitions low at the end of the reference integration period to indicate that data is
stable and may be read through the synchronous serial I/O. The data becomes not valid when DRDY
returns high. The status of DRDY is also available in bit 7 of the ADC_1 register.
The SYNC pin is connected to GND to enable free-running ADC conversions. Alternatively, if SYNC
transitions high, the ADC is immediately driven to the start of the auto-zero time. When SYNC is returned
to a logic low, the next rising edge at pin X2 will start the ADC timing.
The input channel and full scale range may be changed in between ADC conversions, however it is
recommended that such commands be written into the MX844 as soon as possible after pin DRDY
transitions low. This allows the maximum settling time prior to the next ADC conversion.
ADC clock #
0
1023 1024
auto-zero
2047 2048
reference integrate
4095 0
1023 1024
next auto-zero
2047 2048
input integrate
SYNC
DRDY
(active low)
CMP
(active low)
AOUT
6 data bits
DRDY and CMP cleared if ADC_2 register is read
6 data bits
CMP is the digital compare output that is described later. AOUT is the asynchronous serial output of the
ADC.
The ADC output code is offset-binary. An example of the coding is shown here for the +/-50mV range and
the corresponding unipolar range of 0 to 100mV:
Bipolar input
50mV
0 + 1/2 LSB
0 - 1/2 LSB
-50mV
Unipolar input
100mV
50mV + 1/2 LSB
50mV - 1/2 LSB
0
Binary Output (D11:D0)
111111111111
100000000000
011111111111
000000000000
Hexadecimal
FFF
800
7FF
000
Two external components, Rin and Cint, should be chosen such that the value of Cint in pF is 4 to 7 * tAD
and the time constant of Rint * Cint is 300 to 450 * tAD. The value of Rint should be between 47K and
220K ohm. For example, for t(AD) = 1.6 uS, a set of suitable values would be 56K ohm and 10nF (RC =
560uS, ratio = 350). The value of the auto-zero capacitor Caz is typically equal to Cint.
VTRIM is either a no-connect pin or can be used to fine
trim the ADC full scale by +/- 1%. The following circuit
is recommended if fine trimming is desired:
VCC
20K
1K
GND
MX844
Drawing No. 084423
5
08/25/06
www.claremicronix.com
VTRIM
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