CH340 Datasheet (I)
14
below, four power control schemes can be selected. T4 scheme and Q1 scheme (Q1
should choose
N-MOSFET with lower Vth) are simplified schemes. The VDD output voltage is about VCC-0.8V and the
current does not exceed 200mA; T6 scheme and Q3 scheme are complete schemes. D10 in the figure is used
to prevent VDD from supplying power to VCC, which is optional.
7.9. One-click USB download of MCU
(figure below)
The figure above shows the reference circuit for one-click download based on a multi-mode USB to UART
MCU, without manual setting or manual reset.
The type of MCU targeted in the figure above: the MCU itself needs to support one-click download through
the UART. NRST is a reset input (active low). By default, application is selected when BOOT0 is low, and
Boot-Loader is selected when it is high. For example 32F103, etc.
The MCU in the figure above is CH340X. The resistance of the 4.7K
Ω
pull-down resistor can be selected
from 3 to 5.6K
Ω
. This resistor also serves as the BOOT0 pull-down resistor of the MCU. For CH340C with
the last 3 digits of the batch number greater than or equal to B40, OUT# can be used as the second DTR# to
connect to BOOT0.
Note:
For other MCUs with opposite BOOT mode levels, you can directly use CH340C/G DTR# to control
(default high level), or use DTR# of CH340X with a resistor connected between the 6# pin and the 5# pin to
control (push-pull DTR enhanced mode, default high level).
MCU normal working status: The pull-down resistor makes CH340E enter open source DTR enhanced mode.
The 6# pin is switched to DTR#, DTR# is not output by default, BOOT0 remains low, RTS# defaults to high,
and MCU runs applications normally.
CH340 Datasheet (I)
15
One-click download: The computer download tool program opens the UART, sets DTR# to high level, sets
RTS# to
low level and then high level, and the MCU enters the BOOT download program. After the
download
is completed, set DTR# to low level, set RTS#
to low level then high level, the MCU runs the
application normally, and keep DTR# unchanged before closing the UART. Note that the MODEM data and
the pin level are inverted.
Unified power supply mode: CH340X uses the same 5V or 3.3V power supply of MCU. The disadvantage is
that CH340X will consume tens of microamps sleep current.
Independent power supply mode: the CH340X uses the USB VBUS power supply, which does not consume
the MCU power supply current at all. After the power failure of the CH340X itself,
it basically does not
affect the IO of the MCU, but it is necessary to avoid the situation that power is poured back to some MCUs
because the USB is powered but the MCU is not powered. If it is necessary to completely prevent the CH340
power supply from injecting the current to the power-off MCU, refer to the figure in Section 7.7
and add
NMOS and diode.
If NRST pin needs to support additional manual reset, a 1~2K
Ω
resistor or a diode with anode connected to
NRST can be connected in series between RTS# and NRST.