Diodes Incorporated APX811/812: 4-Pin Microprocessor Supervisor With Manual Reset

Features

• Precision monitoring of 2.5V, 3.0V, 3.3V, and 5.0V power supply voltages.
• Full specification over temperature range.
• Manual reset input.
• Available in four output configurations.
• Push-pull RESET output: Active low for APX811, Active high for APX812.
• Power-on reset generator with a fixed delay time of 200ms.
• Available in SOT143 package, with "Green" molding compound (No Br, Sb).
• Lead-Free Finish/RoHS Compliant.

General Description

The APX811/812 are microprocessor supervisory circuits designed to monitor power supplies. They assert a reset signal when the Vcc supply voltage drops below a preset threshold, maintaining the reset for at least 240ms after Vcc rises above the threshold. Reset thresholds are available for various supply voltages. The APX811 features an active-low RESET output, while the APX812 features an active-high RESET output. Both devices include a manual reset input (MR); a low level on MR activates the reset.

These devices are targeted for 2.5V, 3V, 3.3V, and 5V powered systems and are offered with different threshold voltages. They are housed in the space-saving SOT143 package and operate across the industrial temperature range of -40°C to 85°C.

Applications

• Computers
• Controllers
• Intelligent Instruments
• Critical µP and µC power monitoring
• Portable/Battery-powered Equipment
• Automotive

Typical Application Circuit

The typical application circuit shows Vcc connected to the APX811/APX812. A manual reset input (MR) is shown connected to a push button. The device outputs a RESET signal, which is connected to the MCU's RESET input. Ground (GND) is also connected.

Ordering Information

Notes:

1. EU Directive 2002/95/EC (RoHS). For details, visit: www.diodes.com/products/lead_free.html
2. Pad layout information is available in Diodes Inc. document AP02001 at: www.diodes.com/datasheets/ap02001.pdf

Pin Assignments

For the SOT143 package (Top View):

• Pin 1: GND
• Pin 2: RESET (RESET)
• Pin 3: MR
• Pin 4: Vcc

Pin Descriptions

Block Diagram

The block diagram illustrates the internal structure: Vcc is supplied to the device, which includes a voltage reference (Vref), a delay circuit, and a driver. The manual reset input (MR) also influences the delay circuit. The output is a RESET signal.

Absolute Maximum Ratings

Recommended Operating Conditions

Electrical Characteristics (TA = 25°C)

Typical values are at TA=+25°C. Values are specified for TA = -40 to 85°C unless otherwise noted.

Note 3: Test condition for SOT143: Device mounted on FR-4 substrate, 1"x1", 2oz, copper, single-sided, PC boards.

Timing Requirements (TA=25°C)

Switching Characteristics (TA=25°C)

Timing Diagrams

RESET vs. Vcc Timing Diagram: This diagram illustrates the relationship between Vcc and the /RESET signal. It shows that when Vcc drops below the threshold (Vth), the /RESET signal asserts (goes low for APX811, high for APX812). A delay (td) occurs after Vcc rises above Vth before the reset is de-asserted.

RESET vs. /MR Timing Diagram: This diagram shows the effect of the manual reset input (/MR) on the /RESET output. A low pulse on /MR asserts the /RESET output. The diagram also indicates propagation delays (td, tPHL, tPLH) for these transitions.

Typical Performance Characteristics

The document includes several graphs illustrating typical performance:

• RESET Timeout Period vs. Temperature: Shows how the reset timeout period varies with ambient temperature, generally remaining stable between -40°C and 85°C.
• RESET Threshold Voltage vs. Temperature: Displays the reset threshold voltage across the temperature range, indicating slight variations.
• Vcc Supply Current vs. Temperature: Illustrates the supply current consumption at a specific Vcc and threshold voltage (3.3V and 2.93V) as a function of temperature. The current is relatively constant.
• Supply Current vs. Vcc: Plots the supply current against the Vcc voltage, showing an increase in current as Vcc increases.

Application Information

A microprocessor's reset input ensures the processor starts in a known state. The APX811/812 prevents code execution errors during power-up, power-down, or brownout conditions by asserting a reset signal when Vcc falls below a preset threshold or the MR pin is activated. The reset signal is maintained for at least 240ms after Vcc returns above the threshold. The devices feature a push-pull output stage.

For Vcc > 1V, the APX811 reset output is logic low, and the APX812 reset output is logic high. An internal timer holds the reset output for a specified timeout period after Vcc exceeds the reset threshold. If Vcc drops below the threshold (brownout), the reset is re-asserted, and the timer resets. The timer restarts only after Vcc rises above the threshold.

Ensuring a Valid Reset Output Down to Vcc = 0: When Vcc drops below 1V, the APX811's RESET output becomes an open circuit. To ensure a valid low state for low Vcc conditions, a pull-down resistor (e.g., 100kΩ) can be added to the RESET pin. For the APX812, a pull-up resistor (e.g., 100kΩ) between RESET and Vcc is recommended if a valid high state is needed for Vcc < 1V.

Benefits of Highly Accurate Reset Threshold: Unlike supervisors with wider tolerance bands (e.g., ±5%), these ICs offer tighter reset threshold voltages (typically within 5-10% of nominal). This reduces the uncertainty zone where the supply voltage is between the nominal and the reset threshold, ensuring more reliable reset assertion.

Marking Information

The SOT143 package marking includes an identification code (XX), year (Y), and week (W). The identification code varies based on the specific device part number. For example, APX811-46U is marked C2, APX812-46U is marked C9.

Package Information

The SOT143 package has the following dimensions in millimeters:

• Length: 1.78/2.03 mm
• Width: 1.58/1.83 mm
• Height: 0.77/0.93 mm
• Lead-to-lead pitch: 0.37/0.51 mm
• Overall dimensions are provided in a diagram, showing the top and side views with specific measurements for lead spread, body dimensions, and height.

Important Notice

Diodes Incorporated provides this document without warranty of any kind, express or implied, including but not limited to implied warranties of merchantability and fitness for a particular purpose. Diodes Incorporated reserves the right to make changes to the document and products without notice. Diodes Incorporated assumes no liability for the application or use of its products. Customers must assume all risks associated with such use and hold Diodes Incorporated harmless.

Diodes Incorporated products are not authorized for use in life support devices or systems without express written approval. Customers are solely responsible for all safety and regulatory requirements concerning their products and any use of Diodes Incorporated products in safety-critical applications.