NXP Semiconductors MC56F80000-EVKUM, User Manual, Page: 17 / 26

NXP Semiconductors
MC56F80000-EVKUM
MC56F80000-EVK Board User Manual
is a DC signal, which can be used as ADC/CMP input signal through GPIOB6
(ANB6+CMPB_IN1) and GPIOB7 (ANB7+CMPB_IN2).
• OPAMP test configuration
– PGA mode test
When the pin 1 and pin 2 of J15 are connected, J16 is unconnected and J19
is connected, the PGA mode for OPAMP can be tested. The circuit is shown in
Figure 11 . The low frequency PWM signal from GPIOE6 is filtered as DC signal
through the RC filter, the voltage of the DC signal is D*Vdd, where D is the duty cycle
of the PWM signal and Vdd is the voltage of the DSC power supply. The OPAMP
must be configured to work at PGA mode, so the output of the OPAMP should be
Gain*D*Vdd. You can select the gain through OPAMP register configuration. GPIOA1
must be configured as OPAMP non-inverting input in this case.
OPAMP OPAMP
GC
4 GA 1
OPA_OUT
-
+
GE 6/
PWMA_
3
B
GB
6/
GB
7
D*V
dd
v
OPA_OUT
=Gain*D*V
dd
C 76
Gain
X2
X4
X8
X16
OPAMP
GC
4 GA 1
OPA_OUT
-
+
GE 6/
PWMA_
3
B
GB
6/
GB
7
D*V
dd
v
OPA_OUT
=Gain*D*V
dd
C 76
Gain
X2
X4
X8
X16
Figure 11. OPAMP working in PGA mode
– OPAMP mode test
When the pin 2 and pin 3 of J15 are connected, J16 and J19 are both connected,
and GPIOA1 is configured as inverting input, the OPAMP mode for OPAMP can be
tested. You can modify the gain of the OPAMP circuit by changing the value of the
external resistors.
The equivalent circuit is shown in Figure 12 .
Note: The VR which is connected with the non-inverting input of the OPAMP
is a DSC internal 1.2 V voltage reference, which is selected through OPAMP
configuration registers.
OPAMP
VR
R 108
R
109
GC
4 GA 1
GE 6/
PWMA_
3
B
OPA_OUT
-
+
GB
6/
GB
7
v-
v+
C
76
R
110
Figure 12. OPAMP working in OPAMP mode
Since the capacitor C76 filters all the AC component of the PWM signal and has
no impact on the DC component, the equivalent circuit can be obtained as shown
in Figure 13 . The capacitor is removed and the PWM input signal is seen as its DC
component. And the OPAMP works at OPAMP mode, you can calculate the output of
the OPAMP based on the formula in the following figure.
v
OPA_OUT
=VR
(1+
R
109/(
R
108+
R
110))-
D * V
dd
* R 109/( R 108+ R 110)
OPAMP
VR
R 108
R 109
GC 4 GA
1
D*V
dd
OPA_OUT
-
+
GB 6/ GB 7 v-
v+
R 110
Figure 13. Equivalent circuit for OPAMP working in OPAMP mode
MC56F80000-EVKUM All information provided in this document is subject to legal disclaimers. © 2022 NXP B.V. All rights reserved.
User manual Rev. 1 — 14 December 2022
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