LTC2906/LTC2907 Precision Dual Supply Monitors with One Pin-Selectable Threshold and One Adjustable Input U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC®2906/LTC2907 are dual supply monitors intended for systems with multiple supply voltages. The dual supply monitors have a common reset output with delay (200ms for the LTC2906 and adjustable using an external capacitor for the LTC2907). These products provide a precise, space-conscious and micropower solution for supply monitoring. Monitors Two Inputs Simultaneously Three Threshold Selections for 5V, 3.3V or 2.5V Supplies Low Voltage Adjustable Input (0.5V) Three Supply Tolerances (5%, 7.5%, 10%) Guaranteed Threshold Accuracy: ±1.5% of Monitored Voltage Over Temperature Internal VCC Auto Select Power Supply Glitch Immunity 200ms Reset Time Delay (LTC2906 Only) Adjustable Reset Time Delay (LTC2907 Only) Open Drain RST Output Guaranteed RST for V1 ≥ 1V or VCC ≥ 1V Low Profile (1mm) SOT-23 (ThinSOTTM) and Plastic (3mm × 2mm) DFN Packages The LTC2906/LTC2907 feature a tight 1.5% threshold accuracy over the whole operating temperature range and glitch immunity to ensure reliable reset operation without false triggering. The open drain RST output state is guaranteed to be in the correct state for V1 and/or VCC down to 1V. The LTC2906/LTC2907 also feature one adjustable input with a nominal threshold level at 0.5V, another input with three possible input threshold levels, and three supply tolerances for possible margining. These features provide versatility for any kind of system requiring dual supply monitors. Two three-state input pins program the threshold and tolerance level without requiring any external components. U APPLICATIO S ■ ■ ■ ■ Desktop and Notebook Computers Handheld Devices Network Servers Core, I/O Monitor , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATIO Dual Supply Monitor with Adjustable Tolerance (2.5V, 0.8V) Supply Selection Programming V1 2.5V DC/DC CONVERTER SYSTEM LOGIC 0.8V 49.9k LTC2907 TMR S1 GND TOL V1 3.3 OPEN 2.5 GND 0.1µF VCC Tolerance Programming 100k TOLERANCE 22nF TOLERANCE = 10% 5.0 VADJ V1 0.1µF S1 RST 29067 TA01 TOL 5% V1 7.5% OPEN 10% GND 29067f 1 LTC2906/LTC2907 U W W W ABSOLUTE AXI U RATI GS (Notes 1, 2) Terminal Voltages V1, VCC ........................................................ –0.3V to 7V S1, VADJ, TOL ............................ –0.3V to (VMAX + 0.3V) RST ............................................................. –0.3V to 7V RST (LTC2906) ............................................ –0.3V to 7V TMR (LTC2907) ........................................... –0.3V to 7V Operating Temperature Range LTC2906C/LTC2907C .............................. 0°C to 70°C LTC2906I/LTC2907I ............................–40°C to 85°C Storage Temperature Range ..................–65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C U W U PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER LTC2906CDDB LTC2906IDDB LTC2907CDDB LTC2907IDDB TOP VIEW GND 1 8 TOL RST 2 7 S1 RST/TMR* 3 VCC 4 9 6 VADJ 5 V1 DDB8 PACKAGE 8-LEAD (3mm × 2mm) PLASTIC DFN EXPOSED PAD IS GND (PIN 9), MUST BE SOLDERED TO PCB *RST FOR LTC2906 TMR FOR LTC2907 TJMAX = 125°C, θJA = 250°C/W ORDER PART NUMBER LTC2906CTS8 LTC2906ITS8 LTC2907CTS8 LTC2907ITS8 TOP VIEW VCC 1 RST/TMR* 2 RST 3 GND 4 DDB8 PART MARKING LBDC LBDD LBDF LBDG 8 V1 7 VADJ 6 S1 5 TOL TS8 PART MARKING TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 *RST FOR LTC2906 TMR FOR LTC2907 TJMAX = 125°C, θJA = 250°C/W LTBCM LTBCN LTBCP LTBCQ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = V1 = 2.5V, VADJ = 0.55V, S1 = TOL = 0V, unless otherwise noted. (Notes 2, 3, 4) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VRT50 5V, 5% Reset Threshold 5V, 7.5% Reset Threshold 5V, 10% Reset Threshold V1 Input Threshold ● ● ● 4.600 4.475 4.350 4.675 4.550 4.425 4.750 4.625 4.500 V V V VRT33 3.3V, 5% Reset Threshold 3.3V, 7.5% Reset Threshold 3.3V, 10% Reset Threshold V1 Input Threshold ● ● ● 3.036 2.954 2.871 3.086 3.003 2.921 3.135 3.053 2.970 V V V VRT25 2.5V, 5% Reset Threshold 2.5V, 7.5% Reset Threshold 2.5V, 10% Reset Threshold V1 Input Threshold ● ● ● 2.300 2.238 2.175 2.338 2.275 2.213 2.375 2.313 2.250 V V V VRTADJ ADJ, 5% Reset Threshold ADJ, 7.5% Reset Threshold ADJ, 10% Reset Threshold VADJ Input Threshold ● ● ● 0.492 0.479 0.465 0.500 0.487 0.473 0.508 0.495 0.481 V V V VMAX(MIN) Minimum VMAX Operating Voltage (Note 2) RST, RST in Correct Logic State ● 1 V IVCC VCC Input Current VCC > V1 V1 > VCC ● ● 54 100 ±1 µA µA IV1 V1 Input Current VCC > V1 V1 > VCC ● ● 1 55 3 100 µA µA IVADJ VADJ Input Current ±15 nA ● 29067f 2 LTC2906/LTC2907 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = V1 = 2.5V, VADJ = 0.55V, S1 = TOL = 0V, unless otherwise noted. (Notes 2, 3, 4) SYMBOL PARAMETER CONDITIONS ITMR(UP) TMR Pull-Up Current (LTC2907) VTMR = 0V ● ITMR(DOWN) TMR Pull-Down Current (LTC2907) VTMR = 1.4V ● 1.5 2.1 2.7 µA tRST Reset Time-Out Period (LTC2906) ● 140 200 260 ms tRST Reset Time-Out Period (LTC2907) ● 140 200 260 ms tUV VX Undervoltage Detect to RST or RST VX Less Than Reset Threshold VRTX by More than 1% VOL Output Voltage Low RST, RST I = 2.5mA I = 100µA; V1 and/or VCC = 1V (RST Only) ● ● VOH Output Voltage High RST, RST (Notes 2, 5) I = –1µA ● VMAX – 1 CTMR = 22nF MIN TYP MAX UNITS –1.5 –2.1 –2.7 µA µs 150 0.15 0.05 0.4 0.3 V V V Three-State Inputs S1, TOL VIL Low Level Input Voltage ● VIH High Level Input Voltage ● 1.4 VZ Pin Voltage when Left in Hi-Z State ● 0.7 IVPG I = –10µA I = 0µA I = 10µA V V ● 1.1 V V V ● ±25 µA 0.9 Programming Input Current (Note 6) Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The greater of V1, VCC is the internal supply voltage (VMAX). Note 3: All currents into pins are positive; all voltages are referenced to GND unless otherwise noted. Note 4: For reset thresholds test conditions refer to the voltage threshold programming table in the Applications Information section. 0.4 Note 5: The output pins RST and RST have an internal pull-up to VMAX of typically –6µA. However, an external pull-up resistor may be used when faster rise time is required or for VOH voltages greater than VMAX. Note 6: The input current to the three-state input pins are the pull-up and the pull-down current when the pins are either set to V1 or GND respectively. In the open state, the maximum leakage current to V1 or GND permissible is 10µA. U W TYPICAL PERFOR A CE CHARACTERISTICS Specifications are at TA = 25°C unless otherwise noted. 5V Threshold Voltage vs Temperature 3.3V Threshold Voltage vs Temperature 4.75 2.5V Threshold Voltage vs Temperature 3.12 2.375 4.65 4.60 7.5% 4.55 4.50 4.45 10% 4.40 4.35 –50 –25 25 50 0 TEMPERATURE (°C) 75 100 29067 G01 THRESHOLD VOLTAGE, VRT25 (V) 5% THRESHOLD VOLTAGE, VRT33 (V) THRESHOLD VOLTAGE, VRT50 (V) 5% 4.70 3.07 7.5% 3.02 2.97 10% 2.92 2.87 –50 –25 25 50 0 TEMPERATURE (°C) 75 100 29067 G02 5% 2.325 7.5% 2.275 10% 2.225 2.175 –50 –25 25 50 0 TEMPERATURE (°C) 75 100 29067 G03 29067f 3 LTC2906/LTC2907 U W TYPICAL PERFOR A CE CHARACTERISTICS Specifications are at TA = 25°C unless otherwise noted. ADJ Threshold Voltage vs Temperature 19.5 15.8 V1 = 5V VCC = 3.3V VADJ =0.55V S1 =TOL = 1.4V 5% 0.500 19.0 15.4 15.2 7.5% 0.485 18.5 IVCC (µA) 0.490 18.0 0.470 –50 –25 14.2 25 50 0 TEMPERATURE (°C) 75 14.0 17.0 –50 100 –25 25 50 0 TEMPERATURE (°C) 75 29067 G04 100 –50 500 RESET OCCURS ABOVE CURVE 300 200 100 1000 0 100 10 1 0.1 10p 1 10 100 0.1 COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX) 100p 1n 10n CTMR (FARAD) 100n 215 210 205 200 2 1 0 5 V1 (V) 3 2 1 –1 100 S1 = TOL = VCC = V1 VADJ = 0.55V 10pF CAPACITOR AT RST 4 3 2 1 0 0 1 2 3 4 5 V1 (V) 29067 G10 75 5 0 4 25 50 0 TEMPERATURE (°C) RST Output Voltage vs V1 RST OUTPUT VOLTAGE (V) RST OUTPUT VOLTAGE (V) 3 –25 29067 G09 S1 = TOL = VCC = V1 VADJ = 0.55V 10k PULL-UP RESISTOR 4 3 220 195 –50 1µ 5 S1 = TOL = VCC = V1 VADJ = 0.55V 10k PULL-UP RESISTOR 2 225 RST Output Voltage vs V1 5 1 CRT = 22nF 230 (FILM) 29067 G08 29067 G07 RST Output Voltage vs V1 100 235 RESET TIME OUT PERIOD, tRST (ms) RESET TIME OUT PERIOD, tRST (ms) 600 0 75 Reset Time Out Period (t RST) vs Temperature 10000 4 25 50 0 TEMPERATURE (°C) 29067 G06 Reset Time Out Period (t RST) vs Capacitance (CTMR) 700 400 –25 29067 G05 Typical Transient Duration vs Comparator Overdrive (V1, VADJ) TYPICAL TRANSIENT DURATION (µs) 14.8 14.4 17.5 10% 0.475 RST OUTPUT VOLTAGE (V) 15.0 14.6 0.480 –1 V1 = 2.5V VCC = 3.3V VADJ =0.55V S1 =TOL = 1.4V 15.6 0.495 IV1 (µA) THRESHOLD VOLTAGE, VRTADJ (V) IVCC vs Temperature IV1 vs Temperature 0.505 –1 0 1 2 3 4 5 V1 (V) 29067 G11 29067 G12 29067f 4 LTC2906/LTC2907 U W TYPICAL PERFOR A CE CHARACTERISTICS Specifications are at TA = 25°C unless otherwise noted. RST Pull-Down Current (IRST) vs VMAX 4 RST AT 150mV 3 2 1 RST AT 50mV 0 1.8 VCC = V1 S1 = TOL = GND VADJ = 0.55V NO PULL-UP R 5 4 RST AT 150mV 3 2 1 RST AT 50mV 1 2 3 VMAX (V) 4 0 5 1 2 3 VMAX (V) 29067 G13 1.0 0.8 0.6 0.4 0.2 0 10 30 40 50 60 20 RST PULL-DOWN CURRENT, IRST (mA) –12 –10 –8 –6 –4 –2 2.0 VRT33 VRT50 2.5 3.0 3.5 4.0 VMAX (V) 85°C –40°C 25°C 29067 G19 –8 –6 –4 –2 VRT25 2.5 VRT33 3.0 VRT50 3.5 4.0 VMAX (V) 4.5 5.0 29067 G18 RST Output Voltage High (VOH) vs RST Output Source Current (IRST) IS1, ITOL vs Temperature 20 TOL = V1 = 3.3V VADJ = 0.45V 3.0 S1 = OPEN NO PULL-UP R S1 = TOL = V1 = 3.3V 19 18 17 2.5 2.0 –40°C 1.5 16 15 14 13 85°C 12 1.0 25°C 11 0.5 0 –10 2.0 IS1, ITOL (µA) 2.0 –12 0 5.0 4.5 –14 29067G17 RST OUTPUT VOLTAGE HIGH, VOH (V) RST OUTPUT VOLTAGE HIGH, VOH (V) TOL = V1 = 3.3V VADJ = 0.55V S1 = OPEN NO PULL-UP R 10 30 40 50 60 20 RST PULL-DOWN CURRENT, IRST (mA) 29067G15 3.5 –8 –6 –4 –2 –10 OUTPUT SOURCE CURRENT, IRST (µA) 0.2 TOL = V1 –14 RST Output Voltage High (VOH) vs RST Output Source Current (IRST) 0.5 –12 0.4 0 0 1.0 0.6 RST Pull-Up Current (IRST) vs VMAX –16 29067 G16 1.5 0.8 –16 VRT25 0 1.0 5 RST PULL-UP CURRENT, IRST (µA) –40°C 1.2 –40°C TOL = GND 25°C RST PULL-UP CURRENT, IRST (µA) RST OUTPUT VOLTAGE LOW, VOL (V) 1.4 2.5 4 –18 85°C 25°C 85°C 1.2 RST Pull-Up Current (IRST) vs VMAX 1.8 1.6 1.4 29067 G14 RST Output Voltage Low (VOL) vs RST Pull-Down Current (IRST) V1 = VCC = 5V VADJ = 0.55V S1 = TOL = V1 NO PULL-UP R V1 = VCC = 5V VADJ = 0.45V S1 = TOL = V1 NO PULL-UP R 1.6 0 0 0 3.0 RST Output Voltage Low (VOL) vs RST Pull-Down Current (IRST) RST OUTPUT VOLTAGE LOW, VOL (V) S1 = TOL = VCC = V1 VADJ = 0.55V NO PULL-UP R 5 RST PULL-DOWN CURRENT, IRST (mA) RST PULL-DOWN CURRENT, IRST (mA) RST Pull-Down Current (IRST) vs VMAX –8 –7 –6 –5 –4 –3 –2 –1 OUTPUT SOURCE CURRENT, IRST (µA) 0 290467 G20 10 –50 –25 0 25 50 75 100 TEMPERATURE (°C) 29067 G21 29067f 5 LTC2906/LTC2907 U W TYPICAL PERFOR A CE CHARACTERISTICS Specifications are at TA = 25°C unless otherwise noted. IS1, ITOL vs Temperature –20 –19 S1 = TOL = GND V1 = 3.3V –18 IS1, ITOL (µA) –17 –16 –15 –14 –13 –12 –11 –10 –50 –25 25 50 0 TEMPERATURE (°C) 75 100 29067 G22 U U U PI FU CTIO S (TS8 Package/DDB8 Package) VCC (Pin 1/Pin 4): Optional Power Supply Pin. VCC powers and maintains the correct operation of the RST and RST pins in the complete absence of V1. If V1 is present, the greater of VCC or V1 (VMAX) powers the internal circuitry and the reset outputs. Bypass this pin to ground with a 0.1µF (or greater) capacitor. Tie to V1 when no optional power is available. RST (Pin 2/Pin 3): (LTC2906 Only) Reset Logic Output. When all voltage inputs are above the reset threshold for at least the programmed delay time, this pin pulls low. This pin has a weak pull up to VMAX and may be pulled above VMAX using an external pull-up. TMR (Pin 2/Pin 3): (LTC2907 Only) Reset Delay Time Programming Pin. Attach an external capacitor (CTMR) to GND to set a reset delay time of 9ms/nF. Leaving the pin open generates a minimum delay of approximately 200µs. A 22nF capacitor will generate a 200ms reset delay time. RST (Pin 3/Pin 2): Inverted Reset Logic Output. Pulls low when either V1 or VADJ is below the reset threshold and holds low for programmed delay time after all voltage inputs are above threshold. This pin has a weak pull up to VMAX and may be pulled above VMAX using an external pull-up. GND (Pin 4/Pin 1 and Pin 9): Ground. TOL (Pin 5/Pin 8): Three-State Input for Supply Tolerance Selection (5%, 7.5% or 10%). Refer to Applications Information for tolerance selection chart (Table 3). S1 (Pin 6/Pin 7): The Voltage Threshold Select ThreeState Input. Connect to V1, GND or leave unconnected in open state to select one of three possible input threshold levels (refer to Table 1). VADJ (Pin 7/Pin 6): Adjustable Voltage Input. Bypass this pin to ground with a 0.1µF (or greater) capacitor in a noisy environment. V1 (Pin 8/Pin 1): Voltage Input 1. Select from 5V, 3.3V or 2.5V. Refer to Table 1 for details. The greater of (V1, VCC) is also the internal VCC (VMAX). Bypass this pin to ground with a 0.1µF (or greater) capacitor. 29067f 6 LTC2906/LTC2907 W BLOCK DIAGRA VMAX LTC2906 6µA – RST V1 + VMAX RESISTOR NETWORK POWER DETECT 200ms RESET PULSE GENERATOR VMAX 6µA + VCC – VADJ RST BAND GAP REFERENCE THREE-STATE DECODER GND 2906 BD S1 TOL LTC2907 – V1 TMR VMAX POWER DETECT VMAX RESISTOR NETWORK + 6µA 200ms RESET PULSE GENERATOR VCC + RST – VADJ BAND GAP REFERENCE THREE-STATE DECODER GND 2907 BD S1 TOL 29067f 7 LTC2906/LTC2907 WU W TI I G DIAGRA Vx Monitor Timing VRTX VX tRST tUV RST 1V RST 1V 29067 TD U W U U APPLICATIO S I FOR ATIO Supply Monitoring The LTC2906/LTC2907 are low power, high accuracy dual supply monitoring circuits with an adjustable input and another input with selectable threshold. Reset delay is set to a nominal of 200ms for LTC2906 and is adjustable using an external capacitor for LTC2907. The three-state input pin (S1) selects one of three possible threshold voltage levels for V1. Another three-state input pin sets the supply tolerance (5%, 7.5% or 10%). Both input voltages (V1 and VADJ) must be above predetermined thresholds for the reset not to be invoked. The LTC2906/LTC2907 assert the reset outputs during powerup, power-down and brownout conditions on any one of the voltage inputs. Power-Up The greater of V1, VCC is the internal supply voltage (VMAX). VMAX powers the drive circuits for the RST pin. Therefore, as soon as V1 or VCC reaches 1V during power up, the RST output asserts low. VMAX also powers the drive circuits for the RST pin in the LTC2906. Therefore, RST weakly pulls high when either V1 or VCC reaches at least 1V. Threshold programming is complete, when V1 reaches at least 2.17V. After programming, if any one of the Vx inputs falls below its programmed threshold, RST asserts low (RST weakly pulls high) as long as VMAX is at least 1V. Once both V1 and VADJ inputs rise above their thresholds, an internal timer is started. After the programmed delay time, RST weakly pulls high (RST asserts low). Power-Down On power-down, once either V1 or VADJ drops below its threshold, RST asserts logic low and RST weakly pulls high. VMAX of at least 1V guarantees a logic low of 0.4V at RST. Auxiliary Power If an auxiliary power is available it can be connected to the VCC pin. Since the internal supply voltage (VMAX) is the greater of V1, VCC; a VCC of at least 1V guarantees logic low of 0.4V at RST for voltage inputs (V1 and/or VADJ) down to 0V. Programming Pins The two three-state input pins, S1 and TOL, should be connected to GND, V1 or left unconnected during normal operation. Note that when left unconnected, the maximum leakage current allowable from the pin to either GND or V1 is 10µA. 29067f 8 LTC2906/LTC2907 U W U U APPLICATIO S I FOR ATIO In margining application, the three-state input pins can be driven using a three-state buffer. Note however, the low and high output of the three-state buffer has to satisfy the VIL and VIH of the three-state pin listed in the Electrical Characteristics Table. Moreover, when the three-state buffer is in the high impedance state, the maximum leakage current allowed from the pin to either GND or V1 is 10µA. Monitor Programming R2 =100kΩ is recommended. Once the resistor divider is set in the 5% tolerance mode, there is no need to change the divider for the other tolerance modes (7.5%, 10%) because the internal reference at the noninverting input on the VADJ comparator is scaled accordingly, moving the trip point in 2.5% decrements. Table 2 shows suggested 1% resistor values for various adjustable applications. Table 2. Suggested 1% Resistor Values for the VADJ Inputs Connecting S1 to either GND, or V1, or leaving it in open state selects the LTC2906/LTC2907 V1 input voltage threshold. Table 1 shows the three possible selections of V1 nominal input voltage and their corresponding S1 connection. Table 1. Supply Selection Programming VSUPPLY (V) VTRIP (V) R1 (kΩ) R2 (kΩ) 12 11.25 2150 100 10 9.4 1780 100 8 7.5 1400 100 7.5 7 1300 100 6 5.6 1020 100 V1 S1 5 4.725 845 100 5.0 V1 3.3 3.055 511 100 3.3 OPEN 3 2.82 464 100 GND 2.5 2.325 365 100 Note: Open = open circuit or driven by a three-state buffer in high impedance state with leakage current less than 10µA. 1.8 1.685 237 100 1.5 1.410 182 100 The noninverting input on the VADJ comparator is set to 0.5V when the TOL pin is set high (5% tolerance) (Figure␣ 1) and the high impedance inverting input directly ties to the VADJ pin. 1.2 1.120 124 100 2.5 VTRIP LTC2906/LTC2907 R1 1% 1 0.933 86.6 100 0.9 0.840 68.1 100 0.8 0.750 49.9 100 0.7 0.655 30.9 100 0.6 0.561 12.1 100 – VADJ Tolerance Programming R2 1% + + – 0.5V 29067 F01 Figure 1. Setting the Adjustable Trip Point In a typical application, the VADJ pin connects to a tap point on an external resistive divider between the positive voltage being monitored and ground. The following formula obtains R1 resistor value for a particular value of R2 and a desired trip voltage at 5% tolerance: VTRIP(5%) – 1 R2 R1 = 0.5V The three-state input pin TOL, programs the common supply tolerance for both V1 and VADJ input voltages (5%, 7.5% or 10%). The larger the tolerance the lower the trip threshold. Table 3 shows the tolerances selection corresponding to a particular connection at the TOL pin. Table 3. Tolerance Programming TOLERANCE TOL 5% V1 7.5% OPEN 10% GND 29067f 9 LTC2906/LTC2907 U W U U APPLICATIO S I FOR ATIO Threshold Accuracy Reset threshold accuracy is of the utmost importance in a supply sensitive system. Ideally such a system should not reset while supply voltages are within a specified margin below the rated nominal level. Both of the LTC2906/ LTC2907 inputs have the same relative threshold accuracy. The specification for LTC2906/LTC2907 is ±1.5% of the programmed nominal input voltage (over the full operating temperature range). For example, when the LTC2906/LTC2907 are programmed to handle a 5V input with 10% tolerance (S1 = V1 and TOL = GND, refer to Table 1 and Table 3), it does not issue a reset command when V1 is above 4.5V. The typical 10% trip threshold is at 11.5% below the nominal input voltage level. Therefore, the typical trip threshold for the 5V input is 4.425V. With ±1.5% accuracy, the trip threshold range is 4.425V ±75mV over temperature (i.e. 10% to 13% below 5V). This implies that the monitored system must operate reliably down to 4.35V or 13% below 5V over temperature. The same system using a supervisor with only ±2.5% accuracy needs to work reliably down to 4.25V (4.375V ±125mV) or 15% below 5V, requiring the monitored system to work over a much wider operating voltage range. In any supervisory application, supply noise riding on the monitored DC voltage can cause spurious resets, particularly when the monitored voltage is near the reset threshold. A less desirable but common solution to this problem is to introduce hysteresis around the nominal threshold. Notice however, this hysteresis introduces an error term in the threshold accuracy. Therefore, a ±2.5% accurate monitor with ±1% hysteresis is equivalent to a ±3.5% monitor with no hysteresis. The LTC2906/LTC2907 take a different approach to solve this problem of supply noise causing spurious reset. The first line of defense against this spurious reset is a first order low pass filter at the output of the comparator. Thus, the comparator output goes through a form of integration before triggering the output logic. Therefore, any kind of transient at the input of the comparator needs to be of sufficient magnitude and duration before it can trigger a change in the output logic. The second line of defense is the programmed delay time tRST (200ms for LTC2906 and adjustable using an external capacitor for LTC2907). This delay will eliminate the effect of any supply noise, whose frequency is above 1/ tRST, on the RST and RST output. When either V1 or VADJ drops below its programmed threshold, the RST pin asserts low (RST weakly pulls high). When the supply recovers above the programmed threshold, the reset-pulse-generator timer starts counting. If the supply remains above the programmed threshold when the timer finishes counting, the RST pin weakly pulls high (RST asserts low). However, if the supply falls below the programmed threshold any time during the period when the timer is still counting, the timer resets and starts fresh when the supply next rises above the programmed threshold. Note that this second line of defense is only effective for a rising supply and does not affect the sensitivity of the system to a falling supply. Therefore, the first line of defense that works for both cases of rising and falling is necessary. These two approaches prevent spurious reset caused by supply noise without sacrificing the threshold accuracy. Selecting the Reset Timing Capacitor The reset time-out period for LTC2907 is adjustable in order to accommodate a variety of microprocessor applications. Connecting a capacitor, CTMR, between the TMR pin and ground sets the reset time-out period, tRST. The following formula determines the value of capacitor needed for a particular reset time-out period: CTMR = tRST • 110 • 10–9 [F/s] For example, using a standard capacitor value of 22nF gives a 200ms delay. The graph in Figure 2 shows the desired delay time as a function of the value of the timer capacitor that should be used: 29067f 10 LTC2906/LTC2907 U W U U APPLICATIO S I FOR ATIO Note however, by adding an external pull-up resistor, the pull-up strength on the RST pin is increased. Therefore, if it is connected in a wired-OR connection, the pull-down strength of any single device needs to accommodate this additional pull-up strength. RESET TIME OUT PERIOD, tRST (ms) 10000 1000 100 10 Output Rise and Fall Time Estimation 1 0.1 10p 100p 1n 10n CTMR (FARAD) 100n 1µ 29067 F02 Figure 2. Reset Time-Out Period vs Capacitance Leaving the TMR pin open with no external capacitor generates a reset time-out of approximately 200µs. For long reset time-out, the only limitation is the availability of a large value capacitor with low leakage. The TMR capacitor will never charge if the leakage current exceeds the TMR charging current of 2.1µA (typical). RST and RST Output Characteristics The DC characteristics of the RST and RST pull-up and pull-down strength are shown in the Typical Performance Characteristics section. Both RST and RST have a weak internal pull-up to VMAX and a strong pull-down to ground. The weak pull-up and strong pull-down arrangement allows these two pins to have open-drain behavior while possessing several other beneficial characteristics. The weak pull-ups eliminate the need for external pull-up resistors when the rise time on these pins is not critical. On the other hand, the open-drain RST configuration allows for wired-OR connections and can be useful when more than one signal needs to pull-down on the RST line. As noted in the Power-Up and Power-Down sections, the circuits that drive RST and RST are powered by VMAX = MAX (V1, VCC). During fault condition, VMAX of at least 1V guarantees a maximum VOL = 0.4V at RST. However, at VMAX = 1V the weak pull-up current on RST is barely turned on. Therefore, an external pull-up resistor of no more than 100k is recommended on the RST pin if the state and pullup strength of the RST pin is crucial at very low VMAX. The RST and RST output have strong pull-down capability. The following formula estimates the output fall time (90% to 10%) for a particular external load capacitance (CLOAD): tFALL ≈ 2.2␣ •␣ RPD␣ •␣ CLOAD where RPD is the on-resistance of the internal pull-down transistor estimated to be typically 40Ω at VMAX >1V, at room temperature (25°C), and CLOAD is the external load capacitance on the pin. Assuming a 150pF load capacitance, the fall time is about 13ns. The rise time on the RST and RST pins is limited by weak internal pull-up current sources to VMAX. The following formula estimates the output rise time (10% to 90%) at the RST and RST pins: tRISE ≈ 2.2 • RPU • CLOAD where RPU is the on-resistance of the pull-up transistor. Notice that this pull-up transistor is modeled as a 6µA current source in the Block Diagram as a typical representation. The on-resistance as a function of the VMAX = MAX (V1, VCC) voltage (for VMAX > 1V) at room temperature is estimated as follows: RPU = 6 • 105 Ω MAX(V1, VCC ) – 1V At VMAX = 3.3V, RPU is about 260k. Using 150pF for load capacitance, the rise time is 86µs. A smaller external pullup resistor maybe used if the output needs to pull up faster and/or to a higher voltage. For example, the rise time reduces to 3.3µs for a 150pF load capacitance, when using a 10k pull-up resistor. 29067f 11 LTC2906/LTC2907 U TYPICAL APPLICATIO S 5V, 3.3V Supply Monitor, 5% Tolerance with LED Power Good Indicator VCC V1 3.3V 499Ω 0.1µF 5V LTC2906 845k TOL P0WER GOOD LED S1 100k RST SYSTEM RESET RST 0.1µF VADJ GND 2906 TA02 3.3V, 1.8V Monitor, 7.5% Tolerance with an Auxiliary 5V Supply (5V Not Monitored) VCC V1 3.3V LTC2906 0.1µF TOL S1 237k SYSTEM RESET RST 0.1µF VADJ 100k TMR 22nF 5V 1.8V GND 2907 TA03 29067f 12 LTC2906/LTC2907 U TYPICAL APPLICATIO S 2.5V, 1V Monitor, 10% Tolerance with LED Undervoltage Indicator and 5V High Availability Auxiliary Supply (5V Not Monitored) 1V 86.6k VADJ V1 2.5V LTC2907 0.1µF 100k VCC TMR RST TOL S1 GND 22nF 499Ω 5V 0.1µF 0.1µF LED 2907 TA04 Dual Supply Monitor with Hysteresis, 5% Tolerance (Supplies Rising), 10% Tolerance (After RST Goes Low) 3.3V 511k VADJ 5V V1 LTC2906 100k 0.1µF VCC GND S1 10k RST SYSTEM RESET TOL RST 2906 TA05 Dual Supply Monitor for Tracked/Sequenced Supply 3.3V 0.1µF CGATE 10nF RONB 154k RONA 100k VCC GATE ON IN DC/DC RAMP FB1 FB OUT 2.5V SYSTEM LTC2923 RFA1 RAMPBUF RFB1 0.1µF RTB1 TRACK1 RTA1 RTB2 FB2 TRACK2 RTA2 VCC IN DC/DC FB V1 OUT GND LTC2907 1.8V TOL RST VADJ TMR 237k RFA2 RFB2 22nF 100k S1 GND 292067 TA06 29067f 13 LTC2906/LTC2907 U PACKAGE DESCRIPTIO DDB Package 8-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1702) 0.61 ±0.05 (2 SIDES) R = 0.115 TYP 5 0.56 ± 0.05 (2 SIDES) 3.00 ±0.10 (2 SIDES) 0.675 ±0.05 2.50 ±0.05 1.15 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.20 ±0.05 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.200 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 0.38 ± 0.10 8 2.00 ±0.10 (2 SIDES) 0.75 ±0.05 0 – 0.05 4 0.25 ± 0.05 1 PIN 1 CHAMFER OF EXPOSED PAD (DDB8) DFN 1103 0.50 BSC 2.15 ±0.05 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 29067f 14 LTC2906/LTC2907 U PACKAGE DESCRIPTIO TS8 Package 8-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1637) 0.52 MAX 2.90 BSC (NOTE 4) 0.65 REF 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.22 – 0.36 8 PLCS (NOTE 3) 0.65 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) 1.95 BSC TS8 TSOT-23 0802 NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 29067f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 15 LTC2906/LTC2907 U TYPICAL APPLICATIO Quad Supply Monitor with LED Undervoltage Indicator, 5% Tolerance, 3.3V, 2.5V, 0.8V, 0.6V 0.8V 3.3V 49.9k LTC2907 VADJ V1 V1 TOL 22nF 0.1µF 0.1µF 499Ω VCC VADJ S1 100k TMR S1 GND 12.1k TOL LTC2907 VCC TMR 100k 0.6V 2.5V LED RST GND 22nF RST 2907 TA07 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC690 5V Supply Monitor, Watchdog Timer and Battery Backup 4.65V Threshold LTC694-3.3 3.3V Supply Monitor, Watchdog Timer and Battery Backup 2.9V Threshold LTC699 5V Supply Monitor and Watchdog Timer 4.65V Threshold LTC1232 5V Supply Monitor, Watchdog Timer and Push-Button Reset 4.37V/4.62V Threshold LTC1326/LTC1326-2.5 Micropower Precision Triple Supply Monitor for 5V/2.5V, 3.3V and ADJ 4.725V, 3.118V, 1V Threshold (±0.75%) LTC1536 Precision Triple Supply Monitor for PCI Applications Meets PCI tFAIL Timing Specifications LTC1726-2.5/LTC1726-5 Micropower Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ Adjustable RESET and Watchdog Time-Outs LTC1727-2.5/ LTC1727-5 Micropower Triple Supply Monitor with Open-Drain Reset Individual Monitor Outputs in MSOP LTC1728-1.8/ LTC1728-3.3 Micropower Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package LTC1728-2.5/ LTC1728-5 Micropower Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package LTC1985-1.8 Micropower Triple Supply Monitor with Push-Pull Reset Output 5-Lead SOT-23 Package LTC2900 Programmable Quad Supply Monitor Adjustable RESET, 10-Lead MSOP and 3mm X 3mm 10-Lead DFN Packages LTC2901 Programmable Quad Supply Monitor Adjustable RESET and Watchdog Timer, 16-Lead SSOP Package LTC2902 Programmable Quad Supply Monitor Selectable Tolerance, RESET Disable for Margining Functions, 16-Lead SSOP Package LTC2903 Precision Quad Supply Monitor Ultralow Voltage RESET, 6-Lead SOT-23 Package LTC2904 Three-State Programmable Precision Dual Supply Monitor Adjustable Tolerance, 8-Lead SOT-23 and 3mm × 2mm DFN Packages LTC2905 Three-State Programmable Precision Dual Supply Monitor Adjustable RESET and Tolerance, 8-Lead SOT-23 and 3mm × 2mm DFN Packages 29067f 16 Linear Technology Corporation LT/TP 0304 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2004