MOTOROLA
SEMICONDUCTOR TECHNICAL DATA
Document order number: MC33794/D
Rev 6.0, 04/2003
Product Preview
Electric Field Imaging Device
The 33794 is intended for applications where noncontact sensing of objects
is desired. When connected to external electrodes, an electric field is created.
The 33794 is intended for use in detecting objects in this electric field. The IC
generates a low-frequency sine wave. The frequency is adjustable by using an
external resistor and is optimized for 120 kHz. The sine wave has very low
harmonic content to reduce harmonic interference.
The 33794 also contains support circuits for a microcontroller unit (MCU) to
allow the construction of a two-chip E-field system.
Features
• Supports up to 9 Electrodes and 2 References
• Shield Driver for Driving Remote Electrodes Through Coaxial Cables
• +5.0 V Regulator to Power External Circuit
• ISO-9141 Physical Layer Interface
• Lamp Driver Output
• Watchdog and Power ON Reset Timer
• Critical Internal Nodes Scaled and Selectable for Measurement
• High-Purity Sine Wave Generator Tunable with External Resistor
33794
ELECTRIC FIELD
IMAGING DEVICE
DH SUFFIX
CASE 1291
44-LEAD HSOP
DWB SUFFIX
CASE 1390
54-LEAD SOICW-EP
ORDERING INFORMATION
Device
MC33794DH/R2
MC33794DWB/R2
Temperature
Range (T
A
)
-40 to 85°C
-40 to 85°C
Package
44 HSOP
54 SOICW-EP
33794 Simplified Application Diagram
+12 V
47
µF
Indicator
Lamp
0.1
µF
33794
V
PWR
V
CC
10 nF
Analog_IN
Analog_IN
Analog_IN
Analog_IN
Analog_IN
MCU
ISO_Tx
ISO_Rx
Watchdog
Reset
GPx
LAMP_OUT
LP_CAP
V
CC
LEVEL
V
DD
V
DD_
MON
PWR_MON
LAMP_MON
ISO-9141
LAMP_SENSE
ISO_IN
ISO_OUT
WD_IN REF_A
RST
REF_B
LAMP_CTRL
LAMP_GND
TEST
E1
E2
SIGNAL
10 kΩ
47
µF
ISO-9141 Bus
Monitor (Optional)
10 pF
100 pF
1
2
Field Electrodes
Electrode Select
Shield Disable
4
A, B, C, D
DIS_SHIELD E9
SHIELD
GND
AGND
9
R_OSC
39 kΩ
This document contains certain information on a new product.
Specifications and information herein are subject to change without notice.
© Motorola, Inc. 2003
A,B,C,D
TEST
4
CONTROL
LOGIC
22 kΩ (Nominal)
5.6 kΩ
OSC
E1
–
E9
+ REF_A
–
REF_B
5.6 kΩ
MUX
IN
MUX
OUT
CLK
R_OSC
39 kΩ
DIS_SHIELD
SHIELD
47 kΩ
RECT
LP_CAP
10 nF
GAIN AND
OFFSET
V
DD
V
CC
RST
WD_IN
POR/
WD
V
CC
REG
V
DD
REG
LPF
LEVEL
ATTN
SIGNAL
LAMP_SENSE
LAMP_MON
V
PWR
AGND
GND and HEAT SINK
PWR_MON
V
DD
_
MON
LAMP_GND
LAMP_CTRL
ISO_OUT
ISO_IN
LAMP CKT
ISO-9141
LAMP_OUT
ISO-9141
Figure 1. 33794 Internal Block Diagram
33794
2
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
V
CC
NC
AGND
SHIELD
NC
GND
TEST
E1
E2
E3
E4
E5
E6
E7
E8
E9
REF_A
REF_B
ISO_OUT
ISO_IN
ISO-9141
LAMP_OUT
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
HEAT
SINK
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
V
PWR
NC
V
DD
V
DD_
MON
CLK
R_OSC
LP_CAP
PWR_MON
LEVEL
SIGNAL
A
B
C
D
DIS_SHIELD
LAMP_MON
LAMP_SENSE
NC
LAMP_CTRL
LAMP_GND
WD_IN
RST
HSOP PIN FUNCTION DESCRIPTION
Pin
1
2, 5, 27, 43
3
Pin Name
V
CC
NC
AGND
Formal Name
5.0 V Regulator Output
No connect
Analog Ground
Definition
This output pin requires a 47
µF
capacitor and provides a regulated 5.0 V for the
MCU and for internal needs of the 33794.
These pins may be used at some future date and should be left open.
This pin is connected to the ground return of the analog circuitry. This ground should
be kept free of transient electrical noise like that from logic switching. Its path to the
electrical current return point should be kept separate from the return for GND.
This pin connects to cable shields to cancel cable capacitance.
This pin and metal backing is the IC power return and thermal radiator/conductor.
This pin is normally connected to circuit ground. There are special operating modes
associated with this pin when it is not at ground.
These are the electrode pins. They are connected either directly or through coaxial
cables to the electrodes for measurements. One of these electrodes can be selected
at a time for capacitance measurement. All of the other unselected electrodes are
grounded by an internal switch. The signal at the selected electrode pin is routed to
the shield driver amplifier by an internal switch. All of the coaxial cable shields should
be isolated from ground and connected SHIELD.
These pins can be individually selected like E1 through E9. Unlike E1 through E9,
these pins are not grounded when not selected. The purpose of these pins is to allow
known capacitors to be measured. By using capacitors at the low and high end of the
expected range, absolute values for the capacitance on the electrodes can be
computed.
This pin translates ISO-9141 receive levels to 5.0 V logic levels for the MCU.
This pin accepts data from the MCU to be sent over the ISO-9141 communications
interface. It translates the 5.0 V logic levels from the MCU to transmit levels on the
ISO-9141 bus.
4
6, Heat Sink
7
8–16
SHIELD
GND
TEST
E1–E9
Shield Driver
Ground
Test Mode Control
Electrode Connections
17, 18
REF_A,
REF_B
Reference Connections
19
20
ISO_OUT
ISO_IN
ISO-9141 Output
ISO-9141 Input
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
GND
33794
3
HSOP PIN FUNCTION DESCRIPTION (continued)
Pin
21
22
Pin Name
ISO-9141
LAMP_OUT
Formal Name
ISO-9141 Bus
Lamp Driver
Definition
This pin connects to the ISO-9141 bus. It provides the drive and detects signaling on
the bus and translates it from the bus level to logic levels for the MCU.
This is an active low output capable of sinking current of a typical indicator lamp. One
end of the lamp should be connected to a positive supply (for example, battery
voltage) and the other side to this pin. The current is limited to prevent damage to the
IC in the case of a short or surge during lamp turn-on or burn-out.
This output is intended to generate the reset function of a typical MCU. It has a delay
for power-on reset, level detectors to force a reset when V
CC
is out-of-range high or
low, and a watchdog timer that will force a reset if WD_IN is not asserted at regular
intervals. Timing is derived from the oscillator and will change with changes in the
resistor attached to R_OSC.
This pin must be asserted and deasserted at regular interval in order to prevent
RST
from being asserted. By having the MCU program perform this operation more often
the allowed time, a check that the MCU is running and executing its program is
assured. If this doesn’t occur, the MCU will be reset. If the watchdog function is not
desired, this pin may be connected to CLK to prevent a reset from being issued.
This is the ground for the current from the lamp. The current into LAMP_OUT flows
out through this pin.
This signal is used to control the lamp driver. A high logic level turns on the lamp.
This pin is normally connected to the LAMP_OUT pin. The voltage at this pin is
reduced and sent to LAMP_MON so the voltage at the lamp pin is brought into the
range of the analog-to-digital converter (ADC) in the MCU.
This pin is connected through a voltage divider to the LAMP_SENSE pin. The voltage
divider scales the voltage at this pin so that battery voltage present when the lamp is
off is scaled to the range of the MCU ADC. With the lamp off, this pin will be very close
to battery voltage if the lamp is not burned out and the pin is not shorted to ground.
This is useful as a lamp check.
This pin is used to turn off the shield signal. The purpose of doing this is to be able to
detect that the shield signal is not working or the connection to the coax shields is
broken. If either of these conditions exists, there will be little or no change in the
capacitance measured when the DIS_SHIELD is asserted. If the SHIELD output is
working and properly connected, the capacitance of the coax will not be cancelled
when this pin is asserted and the measured capacitance will appear to change by
approximately the capacitance between the center conductor and the shield in the
coax.
These input pins control which electrode or reference is active. Selection values are
shown in Table 1, Electrode Selection, page 14.
This is the undetected signal being applied to the detector. It has a DC level with the
low radio frequency signal superimposed on it. Care must be taken to minimize DC
loading of this signal. A shift of DC will change the center point of the signal and
adversely affect the detection of the signal.
This is the detected, amplified, and offset representation of the signal voltage on the
selected electrode. Filtering of the rectified signal is performed by a capacitor
attached to LP_CAP.
This is connected through a voltage divider to V
PWR
. It allows reduction of the voltage
so it will fall within the range of the ADC on the MCU.
A capacitor on this pin forms a low pass filter with the internal series resistance from
the detector to this pin. This pin can be used to determine the detected level before
amplification or offset is applied. A 10 nF capacitor connected to this pin will smooth
the rectified signal. More capacitance will increase the response time unnecessarily.
23
RST
Reset
24
WD_IN
Watchdog Input
25
26
28
LAMP_GND
LAMP_CTRL
LAMP_SENSE
Lamp Ground
Lamp Control
Lamp Sense
29
LAMP_MON
Lamp Monitor
30
DIS_SHIELD
Shield Driver Disable
34–31
35
A, B, C, D
SIGNAL
Selector Inputs
Undetected Signal
36
LEVEL
Detected Level
37
PWR_MON
Power Monitor
38
LP_CAP
Low-Pass Filter Capacitor
33794
4
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
HSOP PIN FUNCTION DESCRIPTION (continued)
Pin
39
40
Pin Name
R_OSC
CLK
Formal Name
Oscillator Resistor
Clock
Definition
A resistor from this pin to circuit ground determines the operating frequency of the
oscillator. The 33794 is optimized for operation around 120 kHz.
This pin provides a square wave output at the same frequency as the internal
oscillator. The edges of the square wave coincide with the peaks (positive and
negative) of the sine wave.
This is connected through a voltage divider to V
DD
. It allows reduction of the voltage
so it will fall within the range of the ADC on the MCU.
A capacitor is connected to this pin to filter the internal analog regulated supply. This
supply is derived from V
PWR
.
12 V power applied to this pin will be converted to the regulated voltages needed to
operate the part. It is also converted to 5.0 V (V
CC
) and 8.5 V (V
DD
) to power the
MCU and external devices.
41
V
DD_
MON
V
DD
V
PWR
V
DD
Monitor
V
DD
Capacitor
Positive Power Supply Input
42
44
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
33794
5
Embedded System
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