Chapter 17 Gate Drive Unit (GDUV4)
MC9S12ZVM Family Reference Manual Rev. 1.3
Freescale Semiconductor
656
17.4.8
Current Sense Amplifier and Overcurrent Comparator
The current sense amplifier is usually connected as a differential amplifier( see
). It senses the
current flowing through the external power FET as a voltage across the current sense resistor R
sense
. In
order to measure both positive and negative currents, an external reference has to be used. The output of
the current sense amplifier can be connected to an ADC channel. For more details on ADC channel
assignment, refer to Device Overview Internal Signal Mapping Section. The input offset voltage of the
current sense amplifier can be adjusted with the GCSO[2:0] bits in the GDUCSO register. (see
) The output of the current sense amplifier is connected to the plus input of the overcurrent comparator.
The minus input is driven by the output voltage of a 6 Bit DA converter. The digital input of the DA
converter is {11,GOCTx[3:0]}. In order to use the overcurrent comparator GOCEx and GCSxE have to be
set.
NOTE
If both overcurrent comparators are used both action bits GOCA0 and
GOCA1 must have the same value. For example GOCA0=0 and GOCA1=1
is not allowed. Only GOCA0=GOCA1=1 or GOCA0=GOCA1=0 is
allowed.
Figure 17-23. Current Sense Amplifier Connected as Differential Amplifier
+
-
AMPP[0]
R
sense
V
offset
GCSO0[2:0]
=
AMPM[0]
AMP[0]
R
n
/ a
R
n
V
ref
=
R
p
/ a
R
p
V
sense
Output Voltage to ADC
V
AMP
= a V
sense
+ V
ref
GCSE0
I
-
+
GOCEx
V
oct
GOCTx[3:0]
Overcurrent Condition
a V
sense
+ V
ref
< V
oct
6 bit
DAC
