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MC68HC05V12 Datasheet, PDF (204/246 Pages) Freescale Semiconductor, Inc – HCMOS Microcontreller Unit
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Gauge Drivers
Freescale Semiconductor, Inc.
15.12.1 Minimum Voltage Operation
To maintain accuracy to as low a VBATT voltage as possible, the
following equations should be used to calculate the range of values for
the external components.
VBATT(min) = VGSUP(max) + VDIODE + VPASS
VPASS is the drop across the external P-channel MOSFET at
SF * 12 * ICoil(max)
SF = % of max current driven by all coil drivers in application. Worst
case 0.707 (45o) assumes sin/cos drive algorithm.
VDiode = Drop across reverse battery protection diode at
12 * ICoil(max)
To solve the equation, the factors involved in generating the gauge
supply voltage, VGSUP, must first be calculated due to both internal
tolerances and the tolerances of external resistors RG1 and RG2,
VGSUP = VGSUP(nom) x (1 ± TOL)
VGSUP(nom) is the VGSUP voltage generated with all tolerances set to
0%.
TOL = EGS + TOL(RG1) + TOL(RG2) and includes temperature effects.
RG1 and RG2 are the external resistors used to set the VGSUP voltage.
The internal tolerances are EGS.
The minimum VGSUP voltage required for proper operation is given by
ICoil(max) x [RCoil(max) + RSI(max)]
Where
• RSI is the total of the internal resistances from the transistors and
sense resistor and is found in the electrical specifications.
• ICoil is the minimum required coil current.
• RCoil is the minimum coil resistance including temperature effects.
Technical Data
Gauge Drivers
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MC68HC05V12 — Rev. 2.0
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