MC68HC05V12 Datasheet, PDF (184/246 Pages) Freescale Semiconductor, Inc – HCMOS Microcontreller Unit

Gauge Drivers
Freescale Semiconductor, Inc.
15.4 Coil Drivers
To support both 180° and 360° gauges and to keep the pin count as low
as possible, it is necessary to use two different types of coil drivers:
• Full H-bridge drivers
• Half H-bridge drivers
Major gauges will require two of the full H-bridge drivers and the minor
gauges will require one full H-bridge driver and one half H-bridge driver.
A full H-bridge driver uses two pins and is capable of driving a controlled
current in either direction in a single coil. A half H-bridge driver uses only
one pin and can sink a controlled amount of current in one direction only.
The amount of current flowing through the coils and its direction in the
case of the full H-bridge driver are controlled through the current
magnitude registers (CMR) and the current direction registers (CDR)
described here.
All of the components shown in Figure 15-2 and Figure 15-3 are internal
components except for the gauge coils. The resistive and inductive
properties of the external coils are expected to fall within the ranges of
R_Coil and L_Coil shown in Section 17. Electrical Specifications. The
resistance is important for calculating minimum operating voltages and
power dissipation (see 15.12 External Component Considerations),
and the inductance is important in determining settling time (a part of
t_GCS) and controlling the rate of change of the current driven in the coils.
For consistency, note that the dot on the coil is always connected to
the + pin in the coil driver, or, in the case of the half H-bridge driver, it is
connected to the positive supply pin.
The internal resistor R_I is used to measure how much current is flowing
in the coil. The op-amp shown in this diagram is actually built only once
and is shared among all 12 coil drivers through a multiplexer to reduce
manufacturing variability among drivers. To determine what voltage
must come from the digital-to-analog (D/A) output, the maximum current
level set by the external R_MAX resistor is converted to a reference
voltage input to the D/A. This reference voltage sets the maximum
output voltage of the D/A (with an input of $FF).
Technical Data
Gauge Drivers
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MC68HC05V12 — Rev. 2.0