FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
produce a threshold level. The comparator drives a switch
control circuit which generates a frequency modulated signal
for the output drive. The differential voltage across the sense
resistor provides the feedback necessary to maintain the
desired output current. The output current is continuously
monitored as a differential voltage across the internal sense
resistor. When the current is in recirculation and the driver is
in the off state, the current will decay to the lower limit switch
point. When the current reaches the lower limit, the driver will
turn on to increase the current until the upper limit switch
point is reached. The output current will continue to switch
between the switch points, resulting in the desired average
current. The switch points are set to a fixed ±5% of the
commanded current. The switching frequency and accuracy
are dependent upon the load inductance and resistance,
battery voltage, dither amplitude and frequency, switch points
and the commanded current.
AND/OR COMMAND
The AND/OR Command provides control bits for the
following function:
• Determines AND/OR relation between ON/OFF SPI bit
and PX input pin.
The AND/OR command describes the condition by which
the PX input pin controls the output driver. A logic[0] in the
AND/OR register will OR the PX input pin with the respective
bit in the ON/OFF register. Likewise, a logic[1] in the AND/
OR register will AND the PX input pin with the respective bit
in the ON/OFF register. The AND/OR function is disabled
when the PX input pin is disabled.
SERIAL OUTPUT (SO) RESPONSE REGISTER
Fault reporting is accomplished through the SPI interface.
All logic[1]s received by the MCU via the SO pin indicate fault.
All logic[0]s received by the MCU via the SO pin indicate no
fault. All fault bits are cleared on the positive edge of CS. SO
bits 15 to 0 represent the fault status of outputs 15 to 0. The
timing between two write words must be greater than 450µs
to allow adequate time to sense and report the proper fault
status.
Current dither is a method by which the average current is
increased and decreased through the solenoid valve. The
33800 allows the user to program the frequency and
amplitude of the dither control. Dither amplitude is
implemented by increasing and decreasing the DAC by the
programmed dither value. The rate at which the value
changes is set by the programmed dither frequency. When
reprogramming the dither amplitude or dither frequency, the
update will occur on the start of a positive cycle.
CCD1 CONSTANT CURRENT CONTROLLER
The CCD1 constant current controller is a switching
hysteretic current controller with a superimposed dither. The
controller is designed to provide a programmable constant
current through a solenoid valve. Fluid flow is controlled by
the amount of current run through the solenoid valve.
The maximum value of the output (DAC + Dither) must be
less than 1075mA. When a greater value is programmed the
device will disable the dither on the output. Similarly, the
minimum value of the output (DAC - Dither) must be greater
than 0.0mA. Requesting a lower value will disable the dither
on the output.
The master SPI device sends 16 bit command words to
the 33800 device (see Table 15). The master device sets up
the output current based on the CCD1 Control command.
The IC is capable of sinking an average output current from
0mA to 1075mA (without dither). If operating the device with
dither, the DAC + Dither value must be less than 1075mA or
greater than 0.0mA. Commands outside of this command
range will automatically lock out dither.
ON/OFF CONTROL BIT
The CCD1 output may be used as a standard 1.0A low
side driver. For on/off control, the CCD1_DIS bit int the
CCD1Frequency & Amplitude command must be set to logic
1. This disables the constant current driver and enables the
on/off control. To turn the driver ON a logic 1 is placed in the
ON/OFF control bit. A logic 0 placed in the ON/OFF control
bit will turn the driver OFF.
Programming the solenoid current begins by sending the
CCD1 Control command. The command consists of an
control address, Diagnostic Pull Up Enable bit
(Diag_pu_EN), Dither Disable bit (DTHR_DIS), and a 9-bits
of data for digital to analog conversion (DAC). The data is
received and the DAC provides bias for a comparator to
The protection scheme in low side driver mode operates
the same as constant current mode.
33800
Analog Integrated Circuit Device Data
Freescale Semiconductor
27
FREESCALE [ Freescale ]
