mc33970 Freescale Semiconductor, Inc, mc33970 Datasheet - Page 17

• Manufacturer Part Number: mc33970
• Description: Dual Gauge Driver Integrated Circuit With Improved Damping Algorithms
• Manufacturer: Freescale Semiconductor, Inc

the selected gauge to return the pointer to zero position.
selects the gauge to be commanded.
Address 101 — Gauge Return to Zero Configuration
Register
used to configure the Return to Zero Event (refer to
Table
which the pointer moves during an RTZ event. Also, the
integration blanking time, which is the time immediately
following the transition of a coil from a driven state to an open
state in the RTZ mode, is adjustable with this command.
Finally, this command is used to adjust the threshold of the
RTZ integration register.
development to optimize the RTZ for each application.
Selecting an RTZ step rate resulting in consistently
successful zero detections depends on a clear understanding
of the motor characteristics. Specifically, resonant
frequencies exist due to the interaction between the motor
and the pointer. This command allows movement of the RTZ
pointer speed away from these frequencies. Also, some
motors require a significant amount of time for the pointer to
settle to a steady state position when moving from one full
step position to the next. Consistent and accurate integration
values require the pointer be stationary at the end of the full
step time.
spent at each full step during an RTZ event. Bits RC3:RC0
are used to select a ∆t ranging from 0 ms (0000) to 61.44 ms
(1111) in increments of 4.096 ms (refer to
is multiplied by the factor M, which is defined by bits
RC12:RC11. The product is then added to the blanking time,
selected using bit RC4, to generate the full step time. The
multiplier selected with RC12:RC11 will be 1 (00), 2 (01), or
4 (10) as illustrated in the equations below. Note that the
RC12:RC11 value of 8 (11) is not recommended for use in a
product design application, because of the potential for an
RTZ accumulator internal overflow, due to the long time step.
The blanking time is either 512 µs when RC4 is logic [0], or
.
Table 12. RTZCR SI Register Assignment
Analog Integrated Circuit Device Data
Freescale Semiconductor
Read
Write
Bits
RZ1 (D1) — Return to Zero Direction. This bit commands
• 0 = Return to Zero Disabled
• 1 = Return to Zero Enabled
RZ0 (D0) — Gauge Select: Gauge 0/Gauge 1. This bit
• 0 = Selects Gauge 0
• 1 = Selects Gauge 1
Gauge Return to Zero Configuration Register (RTZCR) is
The values used for this register should be selected during
Bits RC3:RC0, RC12:RC11, and RC4 determine the time
12). It is written to modify the step time, or rate; at
RC12
D12
–
RC11
D11
–
RC10
D10
–
RC9
D9
–
Table
RC8
D8
–
13). The ∆t
RC7
D7
–
Address 101
RC6
D6
768 µs when it is logic [1].The full step time is generated
using the following equations:
When D3:D0 (RC3:RC0) ≠ 0000
When D3:D0 (RC3:RC0) = 0000
step time when the RC:3:RC0 = 0000. The full step time
default value after a logic reset is 12.80 ms
(RC12:RC11 = 00, RC4 = 0, and RC3:RC0 = 0011).
the pointer speed is 1/(FullStep x 2) deg/s.
integrating the EMF present in the non-driven coil during the
RTZ event. The integration circuitry is implemented using a
Sigma-Delta converter resulting in the placement of a value
in the 15-bit RTZ accumulator at the end of each full step. The
value in the RTZ accumulator represents the change in flux
and is compared to a threshold. Values above the threshold
indicate a pointer is moving. Values below the threshold
indicate a stalled pointer, thereby resulting in the cessation of
the RTZ event.
two’s complement. After a full step of integration, a sign bit of
0 is the indicator of an accumulator exceeding the decision
threshold of 0, and the pointer is assumed to still be moving.
Similarly, if the sign bit is logic [1] after a full step of
integration, the accumulator value is negative and the pointer
is assumed to be stopped. The integrator and accumulator
are initialized after each full step. If the PECCR command is
written to clock out the RTZ accumulator values via the SO,
the OD14 bit corresponds to the sign bit of the RTZ
accumulator.
preloaded accumulator for specific gauge, pointer, and full
step combinations. Bits RC10:RC5 are used to offset the
initial RTZ accumulator value, properly detecting a stalled
motor. The initial accumulator value at the start of a full step
of integration is negative. If the accumulator was correctly
preloaded, a free-moving pointer will result in a positive value
at the end of the integration time, and a stalled pointer will
result in a negative value. The preloaded values associated
with each combination of bits RC10:RC5 are illustrated in
Table
resulting in an accumulator MSB to a logic [1] when the motor
is stalled. For the default mode, after a power-up or any reset,
the 33970 device sets the accumulator value to -1.
–
Full Step (t) =
Full Step (t) = blanking (t) + 2.048 ms(2)
Note In equation (2), a 2.048 ms offset is added to the full
If there are two full steps per degree of pointer movement,
Detecting pointer movement is accomplished by
The RTZ accumulator bits are signed and represented in
Accurate pointer stall detection depends on a correctly
14. The accumulator should be loaded with a value
RC5
D5
–
∆
RC4
D4
t x M + blanking (t)(1)
–
LOGIC COMMANDS AND REGISTERS
RC3
FUNCTIONAL DEVICE OPERATION
D3
–
RC2
D2
–
RC1
D1
–
RC0
D0
–
33970
17