MICROCHIP MIC2776 Micropower Low Voltage Supervisor Owner’s Manual

MICROCHIP MIC2776 Micropower Low Voltage Supervisor

Product Information

The MIC2776 is a micropower low voltage supervisor. It is available in different package types, including the 5-Lead SOT-23 (M5) package. The product features include undervoltage detection, input current monitoring, reset outputs, manual reset inputs, and internal pull-up current.

Features

• User-Adjustable Input Can Monitor Supplies as Low as 0.3V
• ±1.5% Threshold Accuracy
• Separate VDD Input
• Generates Power-On Reset Pulse (140 ms 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, 3.0 μA Typical
• Rejects Brief Input Transients
• Available in 5-Lead SOT-23 Package

Applications

The MIC2776 can be used in various applications that require low voltage supervision and monitoring, such as microprocessors and other electronic devices.

• Monitoring Processor, ASIC, or FPGA Core Voltage
• Computer Systems
• PDAs/Handheld PCs
• Embedded Controllers
• Telecommunications Systems
• Power Supplies
• Wireless/Cellular Systems
• Networking Hardware

Package Types

• MIC2776 5-Lead SOT-23 (M5) (Top View, H Version)
• MIC2776 5-Lead SOT-23 (M5) (Top View, L and N Versions)

Product Usage Instructions

Before using the MIC2776, please ensure that you follow these instructions:

1. Handle the device with care as it is ESD sensitive. Use recommended handling precautions to prevent damage.
2. The operating voltage range for VDD is 1.5V to 5.5V. Ensure that the voltage supplied is within this range for proper functioning.
3. Connect the appropriate inputs and outputs according to your application requirements.
4. If using the manual reset feature, ensure that the input voltage (V/MR) is below the specified input low voltage (VIL) to trigger a reset.
5. Refer to the timing diagram in Figure 1-1 for understanding the propagation delays and voltage levels.

For detailed electrical characteristics and temperature specifications, please refer to the product manual provided by Microchip Technology Inc. and its subsidiaries.

General Description

The MIC2776 is a power supply supervisor that provides undervoltage monitoring and power-on reset generation in a compact 5-lead SOT-23 package. Features include an adjustable undervoltage 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 300 mV 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 140 ms 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 active at least 140 ms 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 3.0 μA.

Typical Application Circuit

Functional Block Diagram

ELECTRICAL CHARACTERISTICS

Absolute Maximum Ratings †

• Supply Voltage (VDD) ………………………………………………………………………………………………………………….. –0.3V to +7V
• Input Voltages (VIN, V/MR)……………………………………………………………………………………………………………. –0.3V to +7V
• RST, /RST Current ………………………………………………………………………………………………………………………………..20 mA
• ESD Rating (Note 1) …………………………………………………………………………………………………………………………….. 1.5 kV

Operating Ratings ‡

• 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

† Notice: Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and functional operation of the device at those or any other conditions above those indicated in the operational sections of this specification is not intended. Exposure to maximum rating conditions for extended periods may affect device reliability.
‡ Notice : The device is not guaranteed to function outside its operating ratings.
Note 1: Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5 kΩ in series with 100 pF.

ELECTRICAL CHARACTERISTICS

Electrical Characteristics: VDD = 3.3V; TA = +25°C, bold values valid for –40°C ≤ TA ≤ +85°C, unless noted. Note 1

Note 1: VDD operating range is 1.5V to 5.5V. Output is ensured to be asserted down to VDD = 1.2V.

TEMPERATURE SPECIFICATIONS

PIN DESCRIPTIONS

The descriptions of the pins are listed in Table 2-1.

FUNCTIONAL DESCRIPTION

IN, Undervoltage Detector Input
The voltage present at the IN pin is compared to the internal 300 mV 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 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 microcontrollers or microprocessor, the processor will be properly reset at power-on and during power-down and during brown-out conditions. 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 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. Assuming 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 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 100 nA pull-up current to VDD and may be left open if unused.

APPLICATION INFORMATION

Programming the Threshold Voltage

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

EQUATION 4-1:

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 values provides two equations that can be solved for the two unknown resistor values. A value such as 1 MΩ for RTOTAL is a reasonable choice because 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 3 MΩ.
Applying this criteria and rearranging the VTH expression to solve for the resistor values gives:

EQUATION 4-2:

Application Example

Figure 4-1 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 voltage, VI/O, is 2.5V ±5%. As shown in Figure 4-1, 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 ensure that the core supply voltage is adequate to ensure 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 specifications. 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

EQUATION 4-3:

Therefore, solving for VTH results in:

EQUATION 4-4:

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

• R1 = 676.3 kΩ ≈ 673 kΩ
• R2 = 323.7 kΩ ≈ 324 kΩ
• The resulting circuit is shown in Figure 4-1.

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 10 nA. Note that the typical value is a much smaller 5 pA. The magnitude of the offset caused by IIN is given by:

EQUATION 4-5:

The typical error is about three orders of magnitude lower than this—close to 1 µV. 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 optimal. If accuracy is more important than the quiescent current in the resistors, simply reduce the value of RTOTAL to minimize offset errors.

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 open-drain, it can be connected directly to the processor’s reset pin using only the pull-up resistor normally required. See Figure 4-2.

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 4-3, 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.

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 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 VDD = 1.2V, this can be accomplished by adding a pull-down resistor to the /RST output. A value of 100 kΩ 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 4-4. 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 100 kΩ is typical for this application as well. See Figure 4-5.

PACKAGING INFORMATION

Package Marking Information

Note: The Marking Code for the H version is ULAA; the marking code for the L version is UMAA; the marking code for the N version is UKAA.

Legend: XX…X: Product code or customer-specific information
Y: Year code (last digit of calendar year)
YY: Year code (last 2 digits of calendar year)
WW: Week code (week of January 1 is week ‘01’)
NNN: Alphanumeric traceability code
( e 3 ):  Pb-free JEDEC® designator for Matte Tin (Sn) * This package is Pb- free. The Pb-free JEDEC designator ( e 3 ) can be found on the outer packaging for this package.
, ▲, ▼ Pin one index is identified by a dot, delta up, or delta down (triangle mark).
Note: In the event the full Microchip part number cannot be marked on one line, it will be carried over to the next line, thus limiting the number of available characters for customer-specific information. Package may or may not include the corporate logo.
Underbar (_) symbol may not be to scale.

Note: If the full seven-character YYWWNNN code cannot fit on the package, the following truncated codes are used based on the available marking space:

• 6 Characters = YWWNNN;
• 5 Characters = WWNNN;
• 4 Characters = WNNN;
• 3 Characters = NNN;
• 2 Characters = NN;
• 1 Character = N

5-Lead SOT-23 Package Outline and Recommended Land Pattern

Note:
For the most current package drawings, please see the Microchip Packaging Specification located at http://www.microchip.com/packaging

TOP VIEW

SIDE VIEW

5-Lead Plastic Small Outline Transistor (6BX) [SOT231

Note: For the most current package drawings, please see the Microchip Packaging Specification located at <http://www.microchip.com/packaging

Notes:

1. Dimensions D and E1 do not include mold flash or protrusions. Mold flash or protrusions shall not exceed 0.25mm per side.
2. Dimensioning and tolerancing per ASME Y14.5M
   • BSC: Basic Dimension. Theoretically exact value shown without tolerances.
   • REF : Reference Dimension, usually without tolerance, for information purposes only.

5-Lead Plastic Small Outline Transistor (6BX) [SOT23]

Notes:

1. Dimensioning and tolerancing per ASME Y14.5M
   • BSC: Basic Dimension. Theoretically, the exact value is shown without tolerances.

APPENDIX A: REVISION HISTORY

Revision A (August 2022)

• Converted Micrel document MIC2776 to Micro-chip data sheet DS20006705A.
• Minor text changes throughout.

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All Rights Reserved.
ISBN: 978-1-6683-0993-3
2022 Microchip Technology Inc. and its subsidiaries

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References

• Microchip Lightning Support
• Empowering Innovation | Microchip Technology
• Empowering Innovation | Microchip Technology
• Client Support Services | Microchip Technology

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