MIC2785 Datasheet, PDF (5/6 Pages) Micrel Semiconductor – Dual Supply Voltage Monitor with Manual Reset

Micrel, Inc.
Functional Diagram
MIC2785
Application Information
Design and Product Advantages
The MIC2785’s tiny 1.2mm x 1.2mm Thin MLF^® package
combined with no external components offers several
advantages compared to conventional voltage
supervisors.
Tremendous savings are captured with decreased board
size, reduced circuit complexity, and decreased bill of
material (BOM) cost.
Power Supply Input (VDD)
The VDD pin provides a stable input power for the
internal circuitry. This insures that the reference circuitry
and monitoring circuitry have a stable voltage over the
entire operating voltage range.
Supply bypassing is not required. However, bypassing
may be valuable depending on the quality of the system
voltage to which the VDD pin is connected. If bypassing
is added, connect the capacitor(s) as closely as possible
to the VDD pin. Place the lowest value capacitors
closest to the VDD pin.
Under-Voltage Detector Input (VIN)
The largest portion of the monitoring circuitry is the VIN
comparator. The VIN pin is connected to the non-
inverting terminal of the comparator. The internal
reference is connected to the inverting terminal of the
comparator. A reset is triggered when VIN falls below
V_REF. The VIN pin circuitry includes hysteresis to prevent
/RST pin chattering due to noise. The VIN pin is
relatively immune to very brief negative-going transients.
Reset Output (/RST)
The /RST pin is a complementary push-pull output,
which source and sink current. The reset output is
asserted any time the VIN pin voltage is less than the
threshold voltage (V_IN < V_TH) or the /MR pin is asserted.
The /RST pin responds very quickly to reset conditions,
typically asserting within 5µs of V_IN < V_TH.
The MIC2785 securely monitors the supply voltage of
critical components like microcontrollers and
microprocessors. With the MIC2785’s /RST pin
connected to the μP’s reset pin, the processor will be
properly reset at power on and during power-down and
brown-out conditions.
Manual Reset Input (/MR)
The /MR pin provides the ability to initiate a reset via
external logic or a manual switch. This is in addition to
the MIC2785’s automatic voltage monitoring function.
Asserting the /MR input to a logic low causes an
immediate and unconditional reset. Assuming the VIN
pin voltage is within tolerance when /MR is released
(returns high), the reset output will be de-asserted. /MR
is internally pulled-up to VDD and may be left floating/
open if unused.
March 2009
5
M9999-031709-A