mc68hc705v12 Freescale Semiconductor, Inc, mc68hc705v12 Datasheet - Page 190

• Manufacturer Part Number: mc68hc705v12
• Description: M68hc05-based Mcu Hc05 Freescale Semiconductor
• Manufacturer: Freescale Semiconductor, Inc

Gauge Drivers
15.5 Technical Note
Advance Information
NOTE:
An auto-zeroing scheme is implemented in the MC68HC705V12 to
reduce errors internal to the chip. Prior to each coil update, during the
auto-zero phase, the amplifier output is disconnected from all FET gates
(see
On completion of the auto-zero cycle, the amplifier output is connected
to the appropriate FET gate. Since the FET gate and amplifier output are
typically not at the same potential, the FET gate is momentarily pulled
down, until the amplifier control loop re-establishes the correct gate
potential. This abrupt change in gate potential results in voltage spikes,
and thus the current spikes in the gauge coil. The magnitude, duration,
and number of spikes are dependent on the coil resistance, gauge
supply voltage (V
(Figure
test conditions, are shown. Typically, the spike duration and total spike
duration is smaller.
Due to the positive and negative spikes, there is negligible d.c. error
introduced.
I
0
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure
I
I
15-4). Only the worst case spike durations, under the specified
1
1
t
1
Figure 15-4. Specification for Current Spikes
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15-2) while the input is connected to its new input voltage.
GSUP
Gauge Drivers
), and the coil current prior to the auto-zero cycle
t
MAX
t
2
I
I
t
t
t
Conditions: V
0
1
1
2
MAX
= Current before spikes
= Maximum spike magnitude
= (V
= Maximum negative spike duration
= 300 s
= Maximum positive spike duration
= 200 s
= Maximum duration of all spikes
= 500 s
MC68HC705V12
GSUP
L
R
T
Coil
A
GSUP
Coil
+ 0.9 V)/R
= 27 C
= 30 mH
= 200 W (typical)
= 8.00 V
Coil
—
Rev. 3.0