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CS4172
Single Air-Core Gauge Driver
Description
The CS4172 is a monolithic BiCMOS
integrated circuit used to translate a
digital 10-bit word from a micropro-
cessor/microcontroller to complemen-
tary DC outputs. The DC outputs
drive an air-core meter commonly
used in vehicle instrument panels. The
10 bits of data are used to linearly con-
trol the quadrature coils of the meter
directly with a 0.35¡ resolution and
±1.0¡ accuracy over the full 360¡ range
of the gauge. The interface from the
microcontroller is by a Serial Periph-
eral Interface (SPI) compatible serial
connection using up to a 2MHz shift
clock rate.
The digital code, which is directly pro-
portional to the desired gauge pointer
deflection, is shifted into a DAC and
multiplexer. These two blocks provide
a tangential conversion function to
change the digital data into the appro-
priate DC coil voltage for the angle
demanded. The tangential algorithm
creates approximately 40% more
torque in the meter movement than
does a sin-cos algorithm at 45¡, 135¡,
225¡, and 315¡ angles. This increased
torque reduces the error due to pointer
droop at these critical angles.
Each output buffer is capable of sup-
plying up to 80mA per coil and are
controlled by a common enable pin.
When OE is low the output buffers are
turned off but the logic portion of the
chip remains powered and continues
to operate normally.
The Serial Gauge Driver is self-protect-
ed against output short circuit condi-
tions. The output drivers are disabled
anytime the on-chip protection circuit-
ry detects a short circuit condition. The
outputs remain off until a falling edge
is presented on CS. If the short circuit
is still present the output drivers auto-
matically disable themselves again. A
thermal protection circuit limits the
junction temperature to approximately
160¡C for conditions of high supply
voltage and high ambient temperature.
The status pin (ST) reflects the state of
the outputs and is low whenever the
outputs are disabled.
Block Diagram
VCC
VBB
POR
LOGIC
Features
s Serial Input Bus
s 2 MHz Operating
Frequency
s Tangential Drive
Algorithm
s 80mA Drive Circuits
s 0.5¡ Accuracy (Typ.)
s Power-On-Reset
s Protection Features
Output Short Circuit
Overtemperature
Package Options
16 Lead PDIP
SIN- 1
SIN+
Gnd
VBB
SO
SI
VCC
OE
COS+
COS-
Gnd
Gnd
NC
ST
CS
SCLK
SI
SCLK
CS
SO
ST
OE
Serial
to
Parallel
Shift
Register
D0 Ð D6
7 Bit
DAC
D7 Ð D9
VTOP
VVAR
VBAT
R FAULT S
Latch S
POR
MUX
OC
Output
Amplifiers
SIN+
SINÐ
COS+
COSÐ
Gnd
Rev. 4/19/99
1
16 Lead SO Wide
(internally fused leads)
SIN- 1
SIN+
COS+
COS-
VBB SO
Gnd Gnd
Gnd Gnd
SI ST
VCC
CS
OE SCLK
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Email: info@cherry-semi.com
Web Site: www.cherry-semi.com
A ¨ Company

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Absolute Maximum Ratings
Supply Voltage
VBB ....................................................................................................................................................................-1.0V to 15.0V
VCC ......................................................................................................................................................................-1.0V to 6.0V
Digital Inputs ..............................................................................................................................................................-1.0V to 6.0V
Ground Potential Difference (|AGnd-DGnd|)....................................................................................................................0.5V
Steady State Output Current ............................................................................................................................................±100mA
Forced Injection Current (Inputs and Supply).................................................................................................................±10mA
Operating Junction Temperature (TJ) ..................................................................................................................................150¡C
Storage Temperature Range .................................................................................................................................-65¡C to 150¡C
Lead Temperature Soldering
Wave Solder (through hole styles only) .....................................................................................10 sec. max, 260¡C peak
Reflow (SMD styles only) ......................................................................................60 sec. max above 183¡C, 230¡C peak
ESD Susceptibility (Human Body Model)..............................................................................................................................2kV
Electrical Characteristics: -40¡C ² TA ² 105¡C; 7.5V ² VBB ² 14V; 4.5V ² VCC ² 5.5V (unless otherwise specified)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
s Supply Voltages and Currents
VBB Quiescent Current
VCC Quiescent Current
Output disabled (OE = 0V)
[RCOS, RSIN = RL(MIN)] @45¡
(code = XÕ080) VBB = 14V
OE = high, VBB = 0V
SCLK = 2.0MHz
1 5 mA
175 mA
1 mA
s Digital Inputs and Outputs
Output High Voltage
Output Low Voltage
Output High Current
Input High Voltage
Input Low Voltage
Input High Current
Input Low Current
SO, IOH = 0.8mA
SO, IOL =0.8mA
ST, IOL = 2.5mA
ST, VCC = 5.0V
CS, SCLK, SI, OE
CS, SCLK, SI, OE
CS, SCLK, SI, OE; VIN = 0.7 ´ VCC
CS, SCLK, SI, OE; VIN = 0.3 ´ VCC
s Analog Outputs
Output Function Accuracy
Output Shutdown Current,
Source
Output Shutdown Current,
Sink
Output Shutdown Current,
Source
Output Shutdown Current,
Sink
Coil Drive Output Voltage
Minimum Load Resistance
VBB = 14.0V
VBB = 14.0V
VBB = 7.5V
VBB = 7.5V
TA = 105¡C
TA = 25¡C
TA = -40¡C
VCC - 0.8
0.7 ´ VCC
0.4
0.8
25
0.3 ´ VCC
1
1
-1.2 +1.2
70 250
70 250
43 250
43 250
0.748 ´ VBB
229
171
150
V
V
V
µA
V
V
µA
µA
deg
mA
mA
mA
mA
V
½
½
½
2

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Electrical Characteristics: -40¡C ² TA ² 105¡C; 7.5V ² VBB ² 14V; 4.5V ² VCC ² 5.5V (unless otherwise specified)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Shift Clock Frequency
SCLK High Time
SCLK Low Time
SO Rise Time
SO Fall Time
SO Delay Time
SI Setup Time
SI Hold Time
CS Setup Time
CS Hold Time
0.75V to VCC - 1.2V; CL = 90pF
0.75V to VCC - 1.2V; CL = 90pF
CL = 90pF
175
175
75
75
0
75
2.0 MHz
ns
ns
150 ns
150 ns
150 ns
ns
ns
ns
ns
PACKAGE PIN#
16 Lead SO Wide 16 Lead PDIP
11
22
34
4,5,12,13
3,13,14
66
77
88
99
10 10
11 11
14 5
15 15
16 16
12
Package Pin Description
PIN SYMBOL
FUNCTION
SIN-
SIN+
VBB
Gnd
SI
VCC
OE
SCLK
CS
ST
SO
COS-
COS+
NC
Negative output for SINE coil.
Positive output for SINE coil.
Analog supply. Nominally 13.5V.
Ground.
Serial data input. Data present at the rising edge of the
clock signal is shifted into the internal shift register.
5V logic supply. The internal registers and latches are
reset by a POR generated by the rising edge of the voltage
on this pin.
Controls the state of the output buffers. A logic low on
this pin turns them off.
Serial clock for shifting in/out of data. Rising edge shifts
data on SI into the shift register and the falling edge
changes the data on SO.
When high allows data at SI to be shifted into part with
the rising edges of SCLK. The falling edge transfers the
shift register contents into the DAC and multiplexer to
update the output buffers. The falling edge also re-enables
the output drivers if they have been disabled by a fault.
STATUS reflects the state of the outputs and is low any-
time the outputs are disabled, either by OE or the internal
protection circuitry. Requires external pull-up resistor.
Serial data output. Existing 10-bit data is shifted out when
new data is shifted in. Allows cascading of multiple
devices on common serial port.
Negative output for COSINE coil.
Positive output for COSINE coil.
No connection.
3

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Applications Information
Theory of Operation
The SACD is for interfacing between a microcontroller or
microprocessor and air-core meter movements commonly
used in automotive vehicles for speedometers and
tachometers. These movements are built using 2 coils
placed at a 90¡ orientation to each other. A magnetized
disc floats in the middle of the coils and responds to the
magnetic field generated by each coil. The disc has a shaft
attached to it that protrudes out of the assembly. A point-
er indicator is attached to this shaft and in conjunction
with a separate printed scale displays the vehicleÕs speed
or the engineÕs speed.
The disc (and pointer) respond to the vector sum of the
voltages applied to the coils. Ideally, this relationship fol-
sine
lows a cosine equation. Since this is a transcendental and
non-linear function, devices of this type use an approxi-
mation for this relationship. The SACD uses a tangential
algorithm as shown in Figure 1. Only 1 output varies in
any 45 degree range.
Quadrant II
[ ]q = 180¡ Ð Tan-1
VSIN+ Ð VSIN-
VCOS+ Ð VCOS-
For q = 90.176¡ to 134.824¡:
VSIN = 0.748 ´ VBB
VCOS = -Tan(q Ð 90¡) ´ 0.748 ´ VBB
For q = 135.176¡ to 179.824¡:
VSIN = Tan(180¡ Ð q) ´ 0.748 ´ VBB
VCOS = -0.748 ´ VBB
Quadrant III
[ ]q = 180¡ + Tan-1
VSIN+ Ð VSIN-
VCOS+ Ð VCOS-
For q = 180.176¡ to 224.824¡:
VSIN = -Tan(q Ð 180¡) ´ 0.748 ´ VBB
VCOS = -0.748 ´ VBB
SIN+
Output
0°
Max (128)
Min (0)
SINÐ
Output
Max (128)
Min (0)
Degrees of Rotation
45°
90°
135°
180° 225° 270°
315°
360°
COS+
Output
Max (128)
Min (0)
COSÐ
Output
Max (128)
Min (0)
000 001 010
011
100 101
110
111
000
MUX bits (D9 Ð D7)
Figure 1. Major gauge outputs.
Quadrant I
[ ]q = Tan-1
VSIN+ Ð VSIN-
VCOS+ Ð VCOS-
For q = 0.176¡ to 44.824¡:
VSIN = Tanq ´ 0.748 ´ VBB
VCOS = 0.748 ´ VBB
For q = 45.176¡ to 89.824¡:
VSIN = 0.748 ´ VBB
VCOS = Tan(90¡ Ð q) ´ 0.748 ´ VBB
For q = 225.176¡ Ð 269.824¡:
VSIN = -0.748 ´ VBB
VCOS = -Tan(270¡ Ð q) ´ 0.748 ´ VBB
Quadrant IV
[ ]q = 360¡ Ð Tan-1
VSIN+ Ð VSIN-
VCOS+ Ð VCOS-
For q = 270.176¡ to 314.824¡:
VSIN = -0.748 ´ VBB
VCOS = Tan(q Ð 270¡) ´ 0.748 ´ VBB
For q = 315.176¡ Ð 359.824¡:
VSIN = -Tan(360¡ Ð q) ´ 0.748 ´ VBB
VCOS = 0.748 ´ VBB
270°
VSINÐ
VCOS+
360/0°
0.748VBB
q
IV
I
0.748VBB
0.748VBB
III II
0.748VBB
180°
VCOS-
Graph 1. Major gauge response.
4
90°
VSIN+

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Applications Information: continued
To drive the gaugeÕs pointer to a particular angle, the
microcontroller sends a 10-bit digital word into the serial
port. These 10 bits are divided as shown in Figure 2.
However, from a software programmers viewpoint, a
360¡ circle is divided into 1024 equal parts of .35¡ each.
Table 1 shows the data associated with the 45¡ divisions
of the 360¡ driver.
MSB
Major
Gauge
(360°)
D9 D8 D7
D9 Ð D7 select
which octant
LSB
D6 D5 D4 D3 D2 D1 D0
Divides a 45° octant into 128 equal parts
to achieve a .35° resolution
Code 0 Ð 12710
register changes at SO on the falling edge of SCLK. This
arrangement allows the cascading of devices. SO is
always enabled. Data shifts through without affecting the
outputs until CS is brought low. At this time the internal
DAC is updated and the outputs change accordingly.
CS
SCLK
SI(Setup)
SI
CSSetup
SI(Hold)
CSHold
Figure 2. Definition of serial word.
Input Code
(Decimal)
0
128
256
384
512
640
768
896
1023
Ideal
Degrees
0
45
90
135
180
225
270
315
359.65
Nominal
Degrees
0.176
45.176
90.176
135.176
180.176
225.176
270.176
315.176
359.826
VSIN
(V)
0.032
10.476
10.476
10.412
-0.032
-10.476
-10.476
-10.476
-0.032
VCOS
(V)
10.476
10.412
-0.032
-10.476
-10.476
-10.412
0.032
10.476
10.476
SO
SO(tpd)
Figure 3. Serial data timing diagram.
VCC
CS
SI
10 Bits
SO(Rise, Fall)
10% - 90%
10 Bits
Table 1. Nominal output for major gauge (VBB = 14V).
OE
The 10 bits are shifted into the deviceÕs shift register MSB
first using an SPI compatible scheme. This method is
shown in Figure 3. The CS must be high and remain high
for SCLK to be enabled. Data on SI is shifted in on the ris-
ing edge of the synchronous clock signal. Data in the shift
ST
OUTPUTS
ENABLED
Figure 4. Power-up sequence.
OUTPUTS
ENABLED
VBAT
VREG
CS-8156
5V
12V
ENABLE
Application Diagram
360° Gauge
Microcontroller
10k SIN-
COS+
SIN+
COS-
ST VBB
CS
SI
CS4172 VCC
SCLK
OE
SO
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