22
Processor reset
This device has a reset threshold voltage range of 3.00VDC to 3.15VDC. The open-drain, active-low,
reset output goes low for 200ms when triggered and stays low while the voltage supply is below the
threshold. Once the voltage supply rises above the threshold level the output remains low for 200ms.
The SRAM write protection
This circuitry prevents writing to the SRAM and keeps the processor in a RESET state while the
voltage supply is not within specification; POWERUP and POWERDOWN signals are not taken into
account.
This circuit has its chip-enable input connected to the Processor and its chip-enable output to the
SRAM. The chip-enable output goes low only when chip-enable input is low and reset is not asserted.
If chip-enable input is low when a reset occurs, the chip-enable output remains low for 10μs or until
the chip-enable input goes high, whichever occurs first.
Backup switchover
This device provides the supply output for the SRAM; when the voltage supply is above the reset
threshold or backup, the supply output is connected to the voltage supply, otherwise it is connected to
the backup.
Backup circuit
This circuit receives the backup voltage a super capacitor located on Host Board, reduces its
level and feeds the microprocessor supervisory circuit and the RTC with a proper backup voltage.
It consists of a series resistor to limit the current consumption and four zener diodes to limit the
voltage to +3.3VDC.
CPU’s core power source
The CPU’s power source is based on the LM3743MM-300 High-Performance Synchronous Buck
controller in a typical application.
This DC/DC voltage mode PWM buck controller features synchronous rectification at 300 kHz. It delivers
current as needed and step down from an input voltage of +5VDC down to a voltage of +1.2VDC. This
voltage is then fed to the CPU’s core.
The LM3743 provides a set of comprehensive fault protection features such as high-side current limit,
output under-voltage protection, and low-side current limit; if any of these fault protection features is
engaged, it enters into “hiccup” protection. It also ensures a smooth and controlled start-up supporting
pre-biased outputs.
Memory and peripherals’ power source
The Memory and peripherals’ power source is based on the LM5642X Dual Synchronous Buck Converter
in a typical two channel application circuit.
To Next Page
Loading...
Need help?
General
