MIC2774 Dual Micro-Power Low Voltage Supervisor General Description Features The MIC2774 is a dual power supply supervisor that provides undervoltage monitoring, manual reset capability, and power-on reset generation in a compact 5-pin SOT-23 package. Features include two undervoltage detectors, one fixed and one adjustable, and a choice of reset outputs. One undervoltage detector compares VDD against a fixed threshold. Ten factory-programmed thresholds are available. The second, user-adjustable input is compared against a 300mV reference. This low reference voltage allows for the monitoring of voltages lower than those supported by previous supervisor ICs. • Monitors two independent power supplies for undervoltage conditions • One fixed and one user-adjustable input • Choice of ten factory-programmed thresholds • Adjustable input can monitor supplies as low as 0.3V • Generates 140ms (min.) power-on reset pulse • Manual reset input • Choice of active-high, active-low, or open-drain activelow reset outputs • Inputs may be pulled above VDD (7V abs. max.) • /RST output valid down to 1.2V • Ultra-low supply current, 3.5µA typical • Rejects brief input transients • IttyBitty™ 5-pin SOT-23 package • Pin-compatible upgrade for MAX6306/09/12 The reset outputs are asserted at power-on and at any time either voltage drops below the programmed threshold voltage and remains asserted for 140ms (min.) after they subsequently rise back above the threshold boundaries. Manual reset functionality can be provided by a switch connected between ground and the /MR input. A wide choice of voltage thresholds provides for a variety of supply voltages and tolerances. Hysteresis is included to prevent chattering due to noise. Typical supply current is a low 3.5µA. Datasheets and support documentation are available on Micrel’s website at: www.micrel.com. Applications • Monitoring processor ASIC or FPGA core and I/O voltages • PDAs, hand-held PCs • Embedded controllers • Telecommunications systems • Power supplies • Wireless/cellular systems • Networking hardware Typical Application IttyBitty is a trademark of Micrel, Inc. Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com March 16, 2015 Revision 2.0 Micrel, Inc. MIC2774 Ordering Information (1,2) (1,3) Part Number Marking Reset Output Junction Temperature Range Package (4) MIC2774N-XXYM5 UGXX Open-Drain. Active-Low (/RST) –40°C to +85°C SOT-23-5 MIC2774H-XXYM5 UHXX Active-High. Complementary (RST) –40°C to +85°C SOT-23-5 MIC2774L-XXYM5 UIXX Active-Low. Complementary (/RST) –40°C to +85°C SOT-23-5 Note: 1. XX = voltage code, see table below. 2. Order entry part number, add “ TR”. Example: MIC2774N-22YM5 TR. 3. Underbar symbol (__) may not be to scale. 4. Standard reel SOT-23: Reel diameter is 7 inches, hub diameter is 2 inches, width is 8mm. Standard Voltage Options(5) Voltage Code Typical Application (VDD) Nominal Threshold Voltage (VTH) 46 5.0V ±5% 4.68V 44 5.0V ±10% 4.43V 31 3.3V ±5% 3.09V 29 3.3V ±10% 2.93V 28 3.0V ±5% 2.81V 26 2.85V ±5% 2.67V 25 2.7V ±5% 2.53V 23 2.5V ±5% 2.34V 22 2.4V ±5% 2.25V 17 1.8V ±5% 1.69V Note: 5. There are ten standard versions available with an order increment of 3,000 pieces. Samples of standard versions are normally available from stock. Contact factory for information on non-standard versions. Available in tape-and-reel only. Part Number Convention March 16, 2015 2 Revision 2.0 Micrel, Inc. MIC2774 Pin Configuration SOT-23-5 (M5) “H” Version SOT-23-5 (M5) “L” and “N” Version Pin Description Pin Number MIC2774H Pin Number MIC2774L MIC2774N Digital (Output): Asserted high whenever VIN or VDD falls below the threshold voltage. It will remain asserted for no less than 140ms after VIN and VDD return above the threshold limits. 1 /RST Digital (Output): Asserted low whenever VIN or VDD falls below the threshold voltage. It will remain asserted for no less than 140ms after VIN and VDD return above the threshold limits. (Open-drain for “N” version, requires an external pull-up resistor). 2 GND Ground Digital (Input): Driving this pin low initiates immediate and unconditional reset. Assuming VIN and VDD are above the thresholds 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. 3 3 /MR 4 4 IN 5 5 VDD March 16, 2015 Pin Function RST 1 2 Pin Name Analog (Input): The voltage on this pin is compared to the internal 300mV reference. An undervoltage condition will trigger a reset sequence. Analog (Input): Power supply input for internal circuitry and input to the fixed voltage monitor. The voltage on this pin is compared against the internal reference. An undervoltage condition will trigger a reset sequence. 3 Revision 2.0 Micrel, Inc. MIC2774 Absolute Maximum Ratings(6) Operating Ratings(7) Supply Voltage (VDD) .................................... –0.3V to +7.0V Input Voltages (VIN, V/MR) ............................. –0.3V to +7.0V Output Voltages (V/RST, VRST) ....................... –0.3V to +7.0V RST, (/RST) Current ................................................... 20mA Storage Temperature (Ts)......................... –65°C to +150°C (8) ESD Rating ............................................................... 1.5kV 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 to +0.3V Ambient Temperature (TA) .......................... –40°C to +85°C Package Thermal Resistance (θJA) ........................ 256°C/W Electrical Characteristics(9) Note 10; TA = +25°C, bold values indicate –40°C≤ TA ≤ +85°C, unless noted. Symbol Parameter Condition Min. IDD Supply Current VDD = VIN = VTH + 1.6%; Note 10; /MR, RST, /RST open Typ. Max. 3.5 Units µA VDD Voltage Threshold Undervoltage Threshold on VDD (See Standard Voltage Options table) VHYST VTH1.5% Hysteresis Voltage VTH VTH+ 1.5% 1 V % IN, Undervoltage Detector Input VREF Undervoltage Threshold VHYST Hysteresis Voltage IIN Input Current 295 Note 10 300 305 mV 3 mV 5 pA TMIN ≤ TA ≤ TMAX 10 nA RST, /RST Outputs tPROP Propagation Delay VIN = (VREF(MAX) + 100mV) to VIN = (VREF(MIN) – 100mV), /MR = open tRST Reset Pulse Width TMIN ≤ TA ≤ TMAX VOL RST or /RST Output Voltage Low VOH RST or /RST Output Voltage High (H and L versions) 20 140 µs 280 ms ISINK = 1.6mA; VDD ≥ 1.6V 0.3 V ISINK = 100µA; VDD ≥ 1.2V; Note 11 0.3 V ISOURCE = 500µA; VDD ≥ 1.5V 0.8 × VDD V ISOURCE = 10µA; VDD ≥ 1.2V; Note 11 0.8 × VDD V Notes: 6. Exceeding the absolute maximum ratings may damage the device. 7. The device is not guaranteed to function outside its operating ratings. 8. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 1.5kΩ in series with 100pF. 9. Specification for packaged product only 10. VDD equals nominal “Typical Application (VDD)” as shown in the Standard Voltage Options table. 11. VDD operating range is 1.5V to 5.5V. Output is guaranteed to be asserted down to VDD = 1.2V. March 16, 2015 4 Revision 2.0 Micrel, Inc. MIC2774 Electrical Characteristics(9) Note 10; TA = +25°C, bold values indicate –40°C≤ TA ≤ +85°C, unless noted. Symbol Parameter Condition Min. Typ. Max. Units VIH Input High Voltage Note 10 0.7 × VDD VIL Input Low Voltage Note 10 tPROP Propagation Delay V/MR < (VIL – 100mV); Note 10 5 µs tMIN Minimum Input Pulse Width Reset occurs, V/MR < VIL 33 ns IPU Internal Pull-Up Current IIN Input Current, /MR /MR Inputs V 0.3 × VDD V/MR < VIL % 100 250 nA 100 250 nA Timing Diagram Notes: 12. Propagation delays not shown for clarity. 13. The MIC2774 ignores very brief transients. See the Application Information section for details. March 16, 2015 5 Revision 2.0 Micrel, Inc. MIC2774 Functional Diagram Note: *Pinout and polarity vary by device type. See the Ordering Information table. RST, /RST Reset Output Typically, the MIC2774 is used to monitor the power supplies of intelligent circuits such as microcontrollers and microprocessors. By connecting the appropriate reset output of an MIC2774 to the reset input of a µC or µP, the processor will be properly reset at power-on, power-down, and during brown-out conditions. In addition, asserting /MR, the manual reset input, will activate the reset function. Functional Description IN, Undervoltage 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 chattering due to noise. The comparator on the IN pin is relatively immunue to very brief negative-going transients. The reset output is asserted any time /MR is asserted of if VIN or VDD drops below the corresponding threshold voltage. The reset output remains asserted for tRST(min) after VIN and/or VDD subsequently return above the threshold boundaries and/or /MR is released. A reset pulse is also generated at power-on. Hysteresis isincluded in the comparators to prevent chattering of the output due to noise. VDD Input The VDD pin is both the power supply terminal and a monitored input voltage. The voltage at this pin is continually compared against the internal reference. The trip-point at which a reset occurs is factory-programmed. A reset is triggered if and when VDD falls below the trippoint. Hysteresis is employed to prevent chattering due to noise. The comparator on the VDD input is relatively immune to very brief negative-going transients. March 16, 2015 /MR, Manual Reset Input The ability to initiate a reset via external logic or a manual switch is provided in addition to the MIC2774’s automatic supervisory functions. Driving the /MR input to a logic low causes an immediate and unconditional reset to occur. Assuming VIN and VDD are within tolerance when /MR is released (returns high), the reset output will be deasserted 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. Switch debouncing is performed internally; the switch may be connected directly between /MR and GND. /MR is internally pulled-up to VDD and may be left open if unused. 6 Revision 2.0 Micrel, Inc. MIC2774 above regarding the maximum total value of R1 + R2 are followed, this error contribution will be very small thanks to the MIC2774’s very low input bias current. Application Information Programming the Voltage Threshold Referring to the Typical Application circuit, the voltage threshold on the IN pin is calculated as follows: VIH = VREF × To summarize, the various potential error sources are: (𝑅1+𝑅2) 𝑅2 where VREF = 0.300V 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 slight 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: In order to provide the additional criteria needed to solve for the resistor values, the resistorscan 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 1MΩ 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 3MΩ. Given that the total tolerance on VTH for the IN pin 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, Applying this criteria and rearranging the VIH expression to solve for the resistor values gives: R2 = • therefore, solving for VTH results in VTH = (𝑅𝑇𝑇𝑇𝑇𝑇 )(𝑉𝑅𝑅𝑅) 𝑉𝐼𝐼 𝑉𝐶𝐶𝐶𝐶 (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 = RTOTAL – R2 R1 = 676.3kΩ ≈ 673kΩ Application Example Figure 1 illustrates a hypothetical MIC2774L-23 application in which the MIC2774L-23 is used to monitor the core and I/O supplies of a high-performance CPU or DSP. The core supply, VCORE, in the example is 1.0V ±5%. The main power rail and I/O voltage, VI/O, is 2.5V ±5%. As shown in Figure 1, the MIC2774 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 device’s supply range of 1.5V to 5.5V. 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: 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 device’s voltage reference, etc., the threshold will be set slightly below this value. The potential variation in the MIC2774’s voltage reference (VREF) is specified as ±1.5%. The resistors chosen will have their own tolerance specifications. This example assumes 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 March 16, 2015 VERROR = IIN(max) × (R1||R2) = VERROR = ±1×10 A × 2.189×10 Ω = -8 5 -3 VERROR = ±2.189×10 V = 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 7 Revision 2.0 Micrel, Inc. MIC2774 Transient Response The MIC2774 is inherently immune to very short negative-going glitches. Very brief transients may exceed the voltage thresholds without tripping the output. the resistors, simply reduce the value of RTOTAL to minimize offset errors. In general, as shown in Figure 3 and Figure 4, the narrower the transient, the deeper the threshold overdrive that the MIC2774 will ignore. The graphs represent the typical allowable transient duration for a given amount of threshold overdrive that will not generate a reset. Figure 1. MIC2774 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 MIC2774N’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. Figure 3. Typical Input Transient Response Figure 4. Typical VDD Transient Response Ensuring Proper Operation at Low Supply At VDD levels below 1.2V, the MIC2774’s reset output cannot turn on sufficiently to produce a valid logic-low on /RST. In this situation, 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 MIC2774L will be similarly inoperative at VDD ≤ 1.2V. Figure 2. Interfacing to Bidirectional Reset Pin If a given application requires that /RST be valid below VDD = 1.2V, this can be accomplished by adding a pulldown resistor to the /RST output. A value of 100kΩ is recommended because this is usually an acceptable compromise of quiescent current and pull-down current. The resistor’s value is not critical, however. See Figure 5. March 16, 2015 8 Revision 2.0 Micrel, Inc. MIC2774 These statements also apply to the MIC2774H’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 6. Figure 5. MIC2774L Valid /RST Below 1.2V Figure 6. MIC2774H Valid RST Below 1.2V March 16, 2015 9 Revision 2.0 Micrel, Inc. MIC2774 Package Information and Recommended Landing Pattern(14) SOT-23-5 (M5) Note: 14. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com. March 16, 2015 10 Revision 2.0 Micrel, Inc. MIC2774 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 Micrel, Inc. is a leading global manufacturer of IC solutions for the worldwide high performance linear and power, LAN, and timing & communications markets. The Company’s products include advanced mixed-signal, analog & power semiconductors; high-performance communication, clock management, MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs. Company customers include leading manufacturers of enterprise, consumer, industrial, mobile, telecommunications, automotive, and computer products. Corporation headquarters and state-of-the-art wafer fabrication facilities are located in San Jose, CA, with regional sales and support offices and advanced technology design centers situated throughout the Americas, Europe, and Asia. Additionally, the Company maintains an extensive network of distributors and reps worldwide. Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this datasheet. This information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright, or other intellectual property right. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into 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 use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2004 Micrel, Incorporated. March 16, 2015 11 Revision 2.0