User Manual

7. Hardware reset (HRST) requirement
Since the HRST signal is connected to the hard reset of QT3840BC and is also used to start the linux boot
via RGMII interface, therefore it should be connected to the GPIO pin of the network processor so that it
can be controlled by software. Once the HRST signal is deasserted, the module will start to request tftp
server running on the host processor to fetch the bootloader and firmware image. The HRST should be
keep low for no less than 30ms after the 3.3V supply reaches the nominal voltage.
8. Power Management Unit (PMU)
The power management unit is a new feature integrated into the QT3840 chip and it consists of 3
switching regulators and 3 LDOs. The 3 buck converters are designed specifically to generate 1.1V for
QT3840 core voltage, 1.2V for QT2518B, 1.5V for DDR3. The LDOs provide clean output voltages for
oscillator, RF synthesizer and AFE block. In the latest revision of QTM840 RGMII module design, 1.1V for
QT3840 core voltage is fed by external DC-DC switching regulator instead of PMU in the purpose of
reducing the heat dissipation inside the QT3840 package.
3.3V
HRST
3.3V IN
30ms
QT3840BC
PMU
FEM
3.3V IN
DC-DC SW
1.1V Core
1.2V RFIC4
1.5V DDR3