Datasheet MIC2776L-BM5, MIC2776N-BM5, MIC2776H-BM5 Datasheet (MICREL)

MIC2776 Micrel

MIC2776

Micro-Power Low Voltage Supervisor

Advance Information

General Description

The MIC2776 is a power supply supervisor which provides
under-voltage monitoring and power-on reset generation in a
compact 5-pin SOT package. Features include an adjustable
under-voltage detector, a delay-generator, a manual reset
input, and a choice of active-high, active-low, or open-drain
active-low reset output. The user-adjustable monitoring input
is compared against a 300mV reference. This low reference
voltage allows monitoring voltages lower than those sup­ported by previous supervisor ICs.

The reset output is asserted for no less than 140ms at power­on and any time the input voltage drops below the reference
voltage. It remains asserted for the timeout period after the
input voltage subsequently rises back above the threshold
boundary. A reset can be generated at any time by asserting
the manual reset input, /MR. The reset output will remain
active at least 140ms after the release of /MR. The /MR input
can also be used to daisy-chain the MIC2776 onto existing
power monitoring circuitry or other supervisors. Hysteresis is
included to prevent chattering due to noise. Typical supply
current is a low 3.0µA.

Ordering Information

Features

• User-adjustable input can monitor supplies as low as

0.3V

• ±1.5% threshold accuracy

• Separate VDD input

• Generates power-on reset pulse (140ms min.)

• Manual reset input

• Choice of active-high, active-low or open-drain active­low reset output

• Inputs can be pulled above VDD (7V abs. max.)

• Open-drain output can be pulled above VDD (7V abs.
max.)

• Ultra-low supply current, 3.0µA typical

• Rejects brief input transients

• IttyBitty™ SOT-23-5 package

Applications

• Monitoring processor, ASIC, or FPGA core voltage

• Computer systems

• PDAs/Hand-held PCs

• Embedded controllers

• Telecommunications systems

• Power supplies

• Wireless / cellular systems

• Networking hardware

Part Number Marking Reset Output Temperature Range Package

MIC2776N-BM5 UKAA Open-Drain, Active-Low /RST –40°C to +85°C SOT-23-5

MIC2776H-BM5 ULAA Active-High, Complementary RST –40°C to +85°C SOT-23-5

MIC2776L-BM5 UMAA Active-Low, Complementary /RST –40°C to +85°C SOT-23-5

Typical Application

V

1.0V

CORE

V

2.5V

I/O

R1

R2

Power_Good

Manual
Reset

IttyBitty™ is a trademark of Micrel, Inc.

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 [phone] • fax + 1 [phone] • http://www.micrel.com

MIC2776L

/RST

VDD
IN

/MR GND

September 29, 2000 1 MIC2776

MICROPROCESSOR

VCORE

VI/O

/RESET

GND

MIC2776 Micrel

Pin Configuration

GND

2

RST

VDDIN

GND

2

/RST

13

VDDIN

13

/MR

45

SOT-23-5 (M5)

“L” and “N” Version

/MR

45

SOT-23-5 (M5)

“H” Version

Pin Description

Pin Number Pin Number Pin Name Pin Function

MIC2776H MIC2776L

MIC2776N

1 RST Digital (Output): Asserted high whenever V

voltage. It will remain asserted for no less than 140ms after V
above the threshold limit.

1 /RST Digital (Output): Asserted low whenever V

voltage. It will remain asserted for no less than 140ms after V
above the threshold limit. (open-drain for “N” version)

2 2 GND Ground

3 3 /MR Digital (Input): Driving this pin low initiates an immediate and unconditional

reset. Assuming IN is above the threshold when /MR is released (returns
high), the reset output will be de-asserted no less than 140ms later. /MR
may be driven by a logic signal or a mechanical switch. /MR has an internal
pull-up to VDD and may be left open if unused.

4 4 IN Analog (Input): The voltage on this pin is compared to the internal 300mV

reference. An under-voltage condition will trigger a reset sequence.

5 5 VDD Analog (Input): Independent supply input for internal circuitry.

falls below the reference

IN

falls below the reference

IN

returns

IN

returns

IN

MIC2776 2 September 29, 2000

MIC2776 Micrel

Absolute Maximum Ratings (Note 1)

Supply Voltage (V
Input Voltages (V

RST, (/RST) Current .................................................. 20mA

Storage Temperature (T

ESD Rating, Note 3 ................................................... 1.5kV

) ..................................... –0.3V to +7V

DD

, V

IN

) .............................. –0.3V to +7V

/MR

) ....................... –65°C to +150°C

S

Operating Ratings (Note 2)

Supply Voltage (V
Input Voltages (V
Output Voltages

V

(N version) ..................................... –0.3V to +6.0V

/RST

V

, V

/RST

RST

) .................................. +1.5V to +5.5V

DD

, V

IN

) ........................... –0.3V to +6.0V

/MR

(H and L versions) ....... –0.3V to V

DD

+ 0.3V

Ambient Temperature Range (TA) ............. –40°C to +85°C

Electrical Characteristics

Package Thermal Resistance (θ

VDD = 3.3V; TA = +25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted

Symbol Parameter Condition Min Typ Max Units

I

DD

IN, UNDER-VOLTAGE DETECTOR INPUT

V

REF

V

HYST

I

IN

RESET OUTPUTS (/RST, RST)

t

PROP

t

RST

V

OL

V

OH

MANUAL RESET INPUTS (/MR)

V

IH

V

IL

t

PROP

t

MIN

I

PU

I

IN

Note 1. Exceeding the absolute maximum rating may damage the device.

Note 2. The device is not guaranteed to function outside its operating rating.

Note 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.

Note 4. VDD operating range is 1.5V to 5.5V. Output is guaranteed to be asserted down to VDD = 1.2V.

Supply Current VDD = VIN = 3.3V; /MR, RST, /RST open 3.0 µA

Under-Voltage Threshold TA = 25°C 295 300 305 mV

Hysteresis Voltage 3mv

Input Current 5pA

T

≤ TA ≤ T

MIN

Propagation Delay VIN = (V

V

= (V

IN

MAX

REF(MAX)

REF(MIN)

+ 100mV) to 20 µs
– 100mV)

Reset Pulse Width 140 280 ms

RST or /RST Output Voltage Low I

RST or /RST Output Voltage High I

= 1.6mA; 0.3 V

SINK

VDD ≥ 1.6V

= 100µA; 0.3 V

I

SINK

VDD ≥ 1.2V, Note 4

SOURCE

= 500µA; 0.8V

VDD ≥ 1.5V

(H and L Version Only) I

SOURCE

= 10µA; 0.8V

VDD ≥ 1.2V, Note 4

Input High Voltage 1.5V ≤ VDD ≤ 5.5V 0.7V

Input Low Voltage 1.5V ≤ VDD ≤ 5.5V 0.3V

Propagation Delay V

Minimum Input Pulse Width Reset Occurs, V

/MR

< V

IL

< V

/MR

IL

Internal Pull-Up Current 100 nA

Input Current, /MR V

/MR

< V

IL

) ...................... 256°C/W

JA

10 nA

DD

DD

DD

DD

5 µs

33 ns

100 nA

V

V

V

V

September 29, 2000 3 MIC2776

MIC2776 Micrel

Timing Diagram

V

DD

0V

A

V

V

HYST

REF

A

V

IN

0V

V

OH

V

/MR

V

OL

V

OH

V

RST

V

OL

V

OH

V

/RST

V

OL

t

t

RST

RST

Propagation delays not shown for clarity.

Note A. The MIC2776 ignores very brief transients.

See “Applications Information” for details.

t

RST

>t

min

t

RST

MIC2776 4 September 29, 2000

MIC2776 Micrel

Functional Diagram

V

DD

I

PU

/MR

IN

Delay

V

REF

GND

* Pinout and polarity vary by device type.
See ordering information table.

Functional Description

IN, Under-Voltage Detector Input

The voltage present at the IN pin is compared to the internal
300mV reference voltage. A reset is triggered if and when V
falls below V

. Typically, a resistor divider is used to scale

REF

the input voltage to be monitored such that VIN will fall below
V

as the voltage being monitored falls below the desired

REF

trip-point. Hysteresis is employed to prevent chattering due to
noise.

RST, /RST Reset Output

Typically, the MIC2776 is used to monitor the power supply
of intelligent circuits such as microcontrollers and micropro­cessors. By connecting the reset output of a MIC2776 to the
reset input of a µC or µP, the processor will be properly reset
at power-on and during power-down and brown-out condi-

IN

/RST*

RST*

One Shot

R

Q

S

/Q

MIC2776

tions. In addition, asserting /MR, the manual reset input, will
activate the reset function.

The reset outputs are asserted any time /MR is asserted or if
VIN drops below the threshold voltage. The reset outputs
remain asserted for t

(min) after VIN subsequently returns

RST

above the threshold boundary and /MR is released. A reset
pulse is also generated at power-on.

/MR, Manual Reset Input

The ability to initiate a reset via external logic or a manual
switch is provided in addition to the MIC2776’s automatic
supervisory functions. Driving the /MR input to a logic low
causes an immediate and unconditional reset to occur.
Assuming VIN is within tolerance when /MR is released
(returns high), the reset output will be de-asserted no less
than t

later. /MR may be driven by a logic signal, or

RST

mechanical switch. Typically, a momentary push-button switch
is connected such that /MR is shorted to ground when the
switch contacts close. The switch may be connected directly
between /MR and GND. /MR has an internal 100nA pull-up
current to VDD and may be left open if unused.

September 29, 2000 5 MIC2776

MIC2776 Micrel

Application Information

Programming the Voltage Threshold

Referring to the “Typical Application Circuit”, the voltage
threshold is calculated as follows:

R1 R2

+

VV

=×

TH REF

where V

In order to provide the additional criteria needed to solve for
the resistor values, the resistors can be selected such that the
two resistors have a given total value, that is, R1 + R2 =
R

. Imposing this condition on the resistor values pro-

TOTAL

vides two equations that can be solved for the two unknown
resistor values. A value such as 1MΩ for R
reasonable choice since it keeps quiescent current to a
generally acceptable level while not causing any measurable
errors due to input bias currents. The larger the resistors, the
larger the potential errors due to input bias current (IIN). The
maximum recommended value of R

Applying this criteria and rearranging the VTH expression to
solve for the resistor values gives:

RV

()

R2

=

R1 R R2

=−

TOTAL

Application Example

Figure 1 below illustrates a hypothetical MIC2776 application
in which the MIC2776 is used to monitor the core supply of a
high-performance CPU or DSP. The core supply, V
this example is 1.0V ±5%. The main power rail and I/O
voltage, V

, is 2.5V ±5%. As shown in Figure 1, the MIC2776

I/O

is powered by V
= 2.375V; the maximum is 2.5V +5% = 2.625V. This is well
within the MIC2776’s power supply range of 1.5V to 5.5V.

Resistors R1 and R2 must be selected to correspond to the
V

supply of 1.0V. The goal is to insure that the core

CORE

supply voltage is adequate to insure proper operation, i.e.,
V

≥ (1.0V –5%) = 0.950V. Because there is always a

CORE

small degree of uncertainty due to the accuracy of the
resistors, variations in the devices’ voltage reference, etc.,
the threshold will be set slightly below this value. The poten­tial variation in the MIC2776’s voltage reference is specified
as ±1.5%. The resistors chosen will have their own tolerance
specification. This example will assume the use of 1% accu­rate resistors. The potential worst-case error contribution due
to input bias current can be calculated once the resistor
values are chosen. If the guidelines above regarding the
maximum total value of R1+R2 are followed, this error contri­bution will be very small thanks to the MIC2776’s very low
input bias current.

()

R2

= 0.300V

REF

()

TOTAL

REF

V

TH

. The minimum value of V

I/O

TOTAL

TOTAL

is 3MΩ.

is 2.5V –5%

I/O

is a

CORE

, in

To summarize, the various potential error sources are:

• Variation in V

: specified at ± 1.5%

REF

• Resistor tolerance:
chosen by designer (typically ≤ ±1%)

• Input bias current, IIN:
calculated once resistor values are known, typically
very small

Taking the various potential error sources into account, the
threshold voltage will be set slightly below the minimum
V

specification of 0.950V so that when the actual thresh-

CORE

old voltage is at its maximum, it will not intrude into the normal
operating range of V

. The target threshold voltage will

CORE

be set as follows:

Given that the total tolerance on VTH is [V

tolerance] +

REF

[resistor tolerance]

= ±1.5% + ±1% = ±2.5%,

and V

then V

TH(max)

= V

CORE(min)

CORE(min)

,

= VTH + 2.5% VTH = 1.025 VTH,

therefore, solving for VTH results in

V

V=

TH

CORE(min)

1.025

0.950

=

1.025

= 0.9268V

Solving for R1 and R2 using this value for VTH and the
equations above yields:

R1 = 676.3kΩ ≈ 673kΩ

R2 = 323.7kΩ ≈ 324kΩ

The resulting circuit is shown in Figure 1.

Input Bias Current Effects

Now that the resistor values are known, it is possible to
calculate the maximum potential error due to input bias
current, IIN. As shown in the “Electrical Characteristics” table,
the maximum value of IIN is 10nA. (Note that the typical value
is a much smaller 5pA!) The magnitude of the offset caused
by IIN is given by:

V I R1|| R2

ERROR

V 1 10 A 2.189 10 =

ERROR

V 2.189 10 V =

ERROR

V 2.189mV

ERROR

=×

IN(max)

()

=± × × ×−8Ω

=± ×

−

=

5

3

=±

The typical error is about three orders of magnitude lower
than this - close to one

microvolt

! Generally, the error due
to input bias can be discounted. If it is to be taken into
account, simply adjust the target threshold voltage
downward by this amount and recalculate R1 and R2. The
resulting value will be very close to optimum. If accuracy
is more important than the quiescent current in the
resistors, simply reduce the value of R

TOTAL

to minimize

offset errors.

MIC2776 6 September 29, 2000

MIC2776 Micrel

IN

/RST

VDD

/MR GND

MIC2776L

R1

R2

/RESET

VCC

GND

V

CC

Manual
Reset

MICROPROCESSOR

100k
Rpull-down

Ensuring Proper Operation at Low Supply

V

CORE

1.0V ±5%

V

I/O

2.5V ±5%

Manual
Reset

R1
676k
1%

R2
324k
1%

MIC2776

/RST

VDD
IN

/MR GND

MICROPROCESSOR

VCORE

VI/O

/RESET

GND

At levels of V
driver cannot turn on sufficiently to produce a valid logic-low
on the /RST output. In this situation, other circuits driven by
/RST could be allowed to float, causing undesired operation.
(In most cases, however, it is expected that the circuits driven
by the MIC2776L will be similarly inoperative at VDD ≤ 1.2V.)

If a given application requires that /RST be valid below V
= 1.2V, this can be accomplished by adding a pull-down
resistor to the /RST output. A value of 100kΩ is recom-

below 1.2V, the MIC2776L’s /RST output

DD

DD

mended as this is usually an acceptable compromise of
leakage current and pull-down current. The resistor’s value is

Figure 1. MIC2776 Example Design

Interfacing to Processors With Bidirectional Reset Pins

Some microprocessors have reset signal pins that are bidi­rectional, rather than input only. The Motorola 68HC11 family
is one example. Because the MIC2776N’s output is open­drain, it can be connected directly to the processor’s reset pin

not critical, however. See Figure 4.

The statements above also apply to the MIC2776H’s RST
output. That is, to ensure valid RST signal levels at VDD <

1.2V, a pull-up resistor (as opposed to a pull-down) should be
added to the RST output. A value of 100kΩ is typical for this
application as well. See Figure 5.

using only the pull-up resistor normally required. See Figure 2.

V

CC

MIC2776N

/RST

VDD

R1

IN

R2

/MR GND

Figure 2. Interfacing to Bidirectional Reset Pin

MICROPROCESSOR

VCC

100k

/RESET

GND

Figure 4. MIC2776L Valid /Reset Below 1.2V

Transient Response

The MIC2776 is inherently immune to very short negative­going “glitches.” Very brief transients may exceed the voltage

V

CC

threshold without tripping the output.

As shown in Figure 3, the narrower the transient, the deeper

R1

the threshold overdrive that will be ignored by the MIC2776.
The graph represents the typical allowable transient duration

R2

for a given amount of threshold overdrive that will not gener­ate a reset.

Typical INPUT

Transient Response

40

35

30

25

20

15

10

5

0

MAX. TRANSIENT DURATION (µs)

0 100 200 300

Figure 3. Typical INPUT Transient Response

September 29, 2000 7 MIC2776

RESET COMP. OVERDRIVE, V

REF–VIN

(mV)

Manual
Reset

Figure 5. MIC2776H Valid Reset Below 1.2V

MIC2776H

RST

VDD
IN

/MR GND

MICROPROCESSOR

VCC

100k
Rpull-up

RESET

GND

MIC2776 Micrel

Package Information

1.90 (0.075) REF

0.95 (0.037) REF

3.02 (0.119)

2.80 (0.110)

0.50 (0.020)

0.35 (0.014)

1.75 (0.069)

1.50 (0.059)

1.30 (0.051)

0.90 (0.035)

0.15 (0.006)

0.00 (0.000)

SOT-23-5 (M5)

3.00 (0.118)

2.60 (0.102)

10°

0°

DIMENSIONS:

MM (INCH)

0.20 (0.008)

0.09 (0.004)

0.60 (0.024)

0.10 (0.004)

MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 [phone] FAX + 1 [phone] WEB http://www.micrel.com

This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or

other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.

© 2000 Micrel Incorporated

MIC2776 8 September 29, 2000