Micrel, Inc.

MIC2785

Functional Diagram

Application Information

Design and Product Advantages

The MIC2785’s tiny 1.2mm × 1.2mm Thin QFN 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

VREF. 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

(VIN < VTH) or the /MR pin is asserted. The /RST pin

responds very quickly to reset conditions, typically

asserting within 5µs of VIN < VTH.

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.

May 15, 2015

5

Revision 2.0