MIC2776N-YM5TR - Micrel, Inc. - Datasheet.Directory

November 2005 1 MIC2776

MIC2776 Micrel, Inc.

MIC2776

Micro-Power Low Voltage Supervisor

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 power-

on 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 ac-

tive 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.

Typical Application

/RST

VDD

/MR GND

MIC2776L

/RESET

VCORE

GND

Power_Good

VCORE 1.0V

Manual

Reset

MICROPROCESSOR

VI/O

VI/O 2.5V

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 active-

low 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

Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

IttyBitty™ is a trademark of Micrel, Inc.

MIC2776 Micrel, Inc

MIC2776 2 November 2005

Pin Conﬁguration

RST

VDDIN

/MR

4 5

GND

SOT-23-5 (M5)

“H” Version

/RST

VDDIN

/MR

4 5

GND

SOT-23-5 (M5)

“L” and “N” Version

Pin Description

Pin Number Pin Number Pin Name Pin Function

MIC2776H MIC2776L

MIC2776N

1 RST Digital (Output): Asserted high whenever VIN falls below the reference volt-

age. It will remain asserted for no less than 140ms after VIN returns above

the threshold limit.

1 /RST Digital (Output): Asserted low whenever VIN falls below the reference volt-

age. It will remain asserted for no less than 140ms after VIN returns 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.

Ordering Information

Part Number Reset Output Temperature Range Package

Standard Marking Pb-Free Marking

MIC2776N-BM5 UKAA MIC2776N-YM5 UKAA Open-Drain, Active-Low / RST –40ºC to +85ºC SOT-23-5

MIC2776H-BM5 ULAA MIC2776H-YM5 ULAA Active-High, Complementary RST –40ºC to +85ºC SOT-23-5

MIC2776L-BM5 UMAA MIC2776L-YM5 UMAA Active-Low, Complementary /RST –40ºC to +85ºC SOT-23-5

November 2005 3 MIC2776

MIC2776 Micrel, Inc.

Absolute Maximum Ratings (Note 1)

Supply Voltage (VDD) .......................................–0.3V to +7V

Input Voltages (VIN, V/MR) ...............................–0.3V to +7V

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

Storage Temperature (TS) ........................ –65°C to +150°C

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

Operating Ratings (Note 2)

Supply Voltage (VDD) .................................. +1.5V to +5.5V

Input Voltages (VIN, V/MR) ............................–0.3V to +6.0V

Output Voltages

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

V/RST, VRST (H and L versions) ........ –0.3V to VDD + 0.3V

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

Package Thermal Resistance (θJA) ....................... 256°C/W

Electrical Characteristics

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

Symbol Parameter Condition Min Typ Max Units

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

IN, UNDER-VOLTAGE DETECTOR INPUT

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

VHYST Hysteresis Voltage 3 mv

IIN Input Current 5 pA

TMIN ≤ TA ≤ TMAX 10 nA

RESET OUTPUTS (/RST, RST)

tPROP Propagation Delay VIN = (VREF(MAX) + 100mV) to 20 µs

VIN = (VREF(MIN) – 100mV)

tRST Reset Pulse Width 140 280 ms

VOL RST or /RST Output Voltage Low ISINK = 1.6mA; 0.3 V

VDD ≥ 1.6V

ISINK = 100µA; 0.3 V

VDD ≥ 1.2V, Note 4

VOH RST or /RST Output Voltage High ISOURCE = 500µA; 0.8VDD V

VDD ≥ 1.5V

(H and L Version Only) ISOURCE = 10µA; 0.8VDD V

VDD ≥ 1.2V, Note 4

MANUAL RESET INPUTS (/MR)

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

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

tPROP Propagation Delay V/MR < VIL 5 µs

tMIN Minimum Input Pulse Width Reset Occurs, V/MR < VIL 33 ns

IPU Internal Pull-Up Current 100 nA

IIN Input Current, /MR V/MR < VIL 100 nA

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.

MIC2776 Micrel, Inc

MIC2776 4 November 2005

Timing Diagram

VOH

VOL

V/MR

VIN

VDD

VOH

VOL

tRST

V/RST

tRST

VOH

VOL

VRST

>tmin

AVHYST

VREF

Propagation delays not shown for clarity.

Note A. The MIC2776 ignores very brief transients.

See “Applications Information” for details.

November 2005 5 MIC2776

MIC2776 Micrel, Inc.

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

VIN falls below VREF. Typically, a resistor divider is used to

scale the input voltage to be monitored such that VIN will fall

below VREF as the voltage being monitored falls below the

desired trip-point. Hysteresis is employed to prevent chat-

tering due to noise.

RST, /RST Reset Output

Typically, the MIC2776 is used to monitor the power supply

of intelligent circuits such as microcontrollers and micropro-

cessors. 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-

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

activate the reset function.

Functional Diagram

/MR

MIC2776

* Pinout and polarity vary by device type.

See ordering information table.

VDD

/RST*

RST*

VREF

GND

Delay

One Shot

IPU

The reset outputs are asserted any time /MR is asserted or

if VIN drops below the threshold voltage. The reset outputs

remain asserted for tRST(min) after VIN subsequently returns

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. As-

suming VIN is within tolerance when /MR is released (returns

high), the reset output will be de-asserted no less than tRST

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

switch. Typically, a momentary push-button switch is con-

nected 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.

MIC2776 Micrel, Inc

MIC2776 6 November 2005

Application Information

Programming the Voltage Threshold

Referring to the “Typical Application Circuit”, the voltage

threshold is calculated as follows:

V V R1 R2

TH REF

= × +

( )

where VREF = 0.300V

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 = RTOTAL. Imposing this condition on the resistor val-

ues provides two equations that can be solved for the two

unknown resistor values. A value such as 1MΩ for RTOTAL

is a 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 RTOTAL is 3MΩ.

Applying this criteria and rearranging the VTH expression to

solve for the resistor values gives:

R2 R V

TOTAL REF

( )

R1 = RTOTAL – R2

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, VCORE, in

this example is 1.0V ±5%. The main power rail and I/O volt-

age, VI/O, is 2.5V ±5%. As shown in Figure 1, the MIC2776

is powered by VI/O. The minimum value of VI/O is 2.5V –5%

= 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

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

voltage is adequate to insure proper operation, i.e., VCORE

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

To summarize, the various potential error sources are:

• Variation in VREF: speciﬁed at ±1.5%

• 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 VCORE

speciﬁcation of 0.950V so that when the actual threshold

voltage is at its maximum, it will not intrude into the normal

operating range of VCORE. The target threshold voltage will

be set as follows:

Given that the total tolerance on VTH is [VREF tolerance] +

[resistor tolerance]

= ±1.5% + ±1% = ±2.5%,

and VTH(max) = VCORE(min),

then VCORE(min) = VTH + 2.5% VTH = 1.025 VTH,

therefore, solving for VTH results in

V = V

1.025 =0.950

1.025 = 0.9268V

CORE(min)

Solving for R1 and R2 using this value for VTH and the equa-

tions 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 cal-

culate 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:

VERROR = IIN(max) × (R1||R2) =

VERROR = ±1 × 10-8A × 2.189 ×105Ω =

VERROR = ±2.189 × 10-3V =

VERROR = ±2.189mV

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 RTOTAL to minimize

offset errors.

November 2005 7 MIC2776

MIC2776 Micrel, Inc.

/RST

VDD

/MR GND

MIC2776

676k

324k

/RESET

VCORE

GND

VCORE

1.0V 5%

Manual

Reset

MICROPROCESSOR

VI/O

2.5V 5%

Figure 1. MIC2776 Example Design

Interfacing to Processors With Bidirectional Reset Pins

Some microprocessors have reset signal pins that are bi-

directional, rather than input only. The Motorola 68HC11

family is one example. Because the MIC2776N’s output is

open-drain, it can be connected directly to the processor’s

reset pin using only the pull-up resistor normally required.

See Figure 2.

/RST

VDD

/MR GND

MIC2776N

/RESET

VCC

GND

VCC

MICROPROCESSOR

100k

Figure 2. Interfacing to Bidirectional Reset Pin

Transient Response

The MIC2776 is inherently immune to very short negative-

going “glitches.” Very brief transients may exceed the voltage

threshold without tripping the output.

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

threshold overdrive that will be ignored by the MIC2776. The

graph represents the typical allowable transient duration for a

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

0 100 200 300

RESET COMP. OVERDRIVE, VREF–VIN (mV)

Typical INPUT

Transient Response

Figure 3. Typical INPUT Transient Response

Ensuring Proper Operation at Low Supply

At levels of VDD below 1.2V, the MIC2776L’s /RST output

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 opera-

tion. (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 VDD =

1.2V, this can be accomplished by adding a pull-down resis-

tor to the /RST output. A value of 100kΩ is recommended as

this is usually an acceptable compromise of leakage current

and pull-down current. The resistor’s value is 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.

/RST

VDD

/MR GND

MIC2776L

/RESET

VCC

GND

VCC

Manual

Reset

MICROPROCESSOR

100k

Rpull-down

Figure 4. MIC2776L Valid /Reset Below 1.2V

RST

VDD

/MR GND

MIC2776H

RESET

VCC

GND

VCC

Manual

Reset

MICROPROCESSOR

100k

Rpull-up

Figure 5. MIC2776H Valid Reset Below 1.2V

MIC2776 Micrel, Inc

MIC2776 8 November 2005

Package Information

SOT-23-5 (M5)

MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com

This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.

Micrel reserves the right to change circuitry and speciﬁcations at any time without notiﬁcation to the customer.

Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can

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the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a signiﬁcant injury to the user. A Purchaser's

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