CS4172 Datasheet, PDF (5/8 Pages) Cherry Semiconductor Corporation – Single Air-Core Gauge Driver

Applications Information: continued
To drive the gauge’s 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 – 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 – 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
V_SIN
(V)
0.032
10.476
10.476
10.412
−0.032
−10.476
−10.476
−10.476
−0.032
V_COS
(V)
10.476
10.412
−0.032
−10.476
−10.476
−10.412
0.032
10.412
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 (V_BB = 14V).
OE
The 10 bits are shifted into the device’s 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
V_BAT
V_REG
5V
CS8156 ^12V
ENABLE
Application Diagram
360° Gauge
Microcontroller
10k
SIN−
COS+
SIN+
COS−
ST
V_BB
CS
SI
CS4172 ^VCC
SCLK
OE
SO
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