MCF8329HS-Q1 integrates a high-performance low-side
current sense amplifier for current measurements using a low-side shunt resistor.
Low-side current measurements are used for multiple control features and protections
in MCF8329HS-Q1. The current sense amplifiers feature
configurable gain (5 V/V, 10 V/V, 20 V/V, and 40 V/V) through EEPROM setting. The
current sense amplifier can support sensing bidirectional current through the
low-side shunt resistor.
MCF8329HS-Q1 internally generates common mode voltage of
VREF/2 to obtain maximum resolution for current measurement for both
the direction of current. VREF is an internally generated reference
voltage having a typical value of 3 V.
Use
Equation 3 to design the value of the shunt resistor (RSENSE)
connected between SP and SN, for the range of current (I) through the low side
single shunt and the selected current sense amplifier gain configured by EEPROM bits
CSA_GAIN.
Equation 3.
Note:
- TI recommends designing the
shunt resistor RSENSE value to limit the current sense amplifier
output voltage (VSO) between 0.25V and 3V across the operating
range of low-side single shunt resistor current (I) at the selected gain of
CSA_GAIN. Appropriately size the shunt resistor power rating based on the
I2RSENSE losses with sufficient margin.
- SINGLE_SHUNT_BLANKING_TIME can be used to set the blanking window for
current sampling (after a PWM edge) till the sensed current settles to a
noise-free, steady value. A higher SINGLE_SHUNT_BLANKING_TIME reduces noise
in sensed current but will also reduce the maximum modulation index that can
be applied - SINGLE_SHUNT_BLANKING_TIME should be suitably set to optimize
between maximum modulation index (motor speed) and minimal noise in sensed
current.
- DYNAMIC_SAMPLING_EN can be set to 1b to enable
dynamic current sampling to reduce the current harmonics caused by blanking
time; when dynamic current sampling is enabled there maybe a DC offset in
motor phase currents.