TMC603A Datasheet, PDF (19/44 Pages) TRINAMIC Motion Control GmbH & Co. KG. – Three phase motor driver with BLDC back EMF commutation hallFX™ and current sensing

TMC603A DATA SHEET (V. 1.15 / 2009-Nov-19)
19
5.3 Current measurement amplifiers
The TMC603 amplifies the voltage drop in the three lower MOSFET transistors in order to allow
current measurement without the requirement for current sense (shunt) resistors. This saves cost and
board space, as well as the additional power dissipation in the shunt resistors. Optional shunt resistors
can be used, e.g. source resistors for each lower MOSFET or a common shunt resistor in the bridge
foot point if a more precise measurement without the need for calibration and temperature
compensation is desired. For the TMC603A, the FILTx pins in this mode are switched as inputs for the
sensing of the shunt resistors. The internal amplifier conditions the signal for a standard
microcontroller.
The TMC603 CURx outputs deliver a signal centered to 1/3 of the 5V VCC supply. This allows
measurement of both, negative and positive signals, while staying compatible to a 3.3V
microcontroller. The current amplifier is an inverting type.
+VCC
SENSE_HI
D
ENRS_TEST
D
BMx
A
FILTx_RSx
A
amplify
5x or 20x
SWC
R
R
1/3 VCC
R
track & hold stage
BLx
D
SAMPLEx
D
autozero
automatic
sample
point delay
add 1/3 VCC
offset
figure 14: schematic of current measurement amplifiers
CURx
A
Pin
CURx
SENSE_HI
SAMPLEx
FILTx_RSx
Comments
Output of current measurement amplifier. The output signal is centered to 1/3 VCC.
Switches current amplifiers to high sensitivity (high level). Control by processor to get
best sensitivity and resolution for measurement.
Optional external control for current measurement sample/hold stage. Set to positive
level, if unused
Input for optional external sense resistor. To enable, tie pin ENRS_TEST to VCC.
This feature has been added in TMC603A.
The voltage drop over the MOSFET (or shunt resistor) is calculated as follows:
whereas x is the ADC output value, x₀ is the ADC output value at zero current (e.g. 85 for an 8 bit ADC
with 5V reference voltage), ADC_MAX is the range of the ADC (e.g. 256 for an 8 bit ADC), V_ADCREF is the
reference voltage of the ADC and A_CUR is the currently selected amplification (absolute value) of the
TMC603.
With this, the motor current can be calculated using the on resistance R_DSON (at 10V) of the MOSFET:
Copyright © 2009 TRINAMIC Motion Control GmbH & Co. KG