NXP Semiconductors
QN9090
QN9090-DK006 Development Kit User Guide
UM11355
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User Guide
Rev.1.0
— 15 January 2020
13 of 19
at 50k to 200ksps. The on-board MAX9634T current monitor measures the voltage
across the QN9090
VBAT Vsense resistor of 3.3Ω. The MAX9634 multiplies the sense
voltage by 25 to provide a voltage range suitable for the ADC to measure. The current
measurement circuit is controlled by the debug processor and is not user programmable.
Power measurement utilities to use this feature are available in the MCUXpresso IDE
installation.
Due to input offset voltage variations in the MAX9634, the current measurement circuit is
not recommended for measuring current below 150uA.
5.2 Vsense resistor measurement
The voltage across a series 3.3Ω resistor with the target QN9090 VBAT can be manually
measured at J14 on the PCB. The voltmeter positive probe is applied to J14 pin 1
(square pad) and negative probe to J14 pin 2. Use Ohm’s law to calculate the current
(QN9090
current = measured voltage / 3.3Ω). As an example, if the measured voltage is
10mV, then 10e-
3 / 3.3Ω = 3.03mA. Note that the input current to the MAX9634 used in
the on-board current measurement will be included in the voltage measured across this
resistor.
5.3 Current measurement with a multimeter
Figure 8 is the circuit for the power supply to the module. The signal VBAT is used to
power the QN9090 module
Figure 8 Power Sensing Circuit
This signal goes to the module (JM1.17) and the expansion connector (J3.31)
