MIC1557YM5 TR

**MIC1555/1557** 

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## **IttyBitty™ RC Timer / Oscillator** 

## **General Description** 

The MIC1555 IttyBitty™ CMOS RC timer/oscillator and MIC1557 IttyBitty CMOS RC oscillator are designed to provide rail-to-rail pulses for precise time delay or frequency generation. 

The devices are similar in function to the industry standard “555”, without a frequency control (FC) pin or an opencollector discharge (D) pin. The threshold pin (TH) has precedence over the trigger (TR) input, ensuring that the BiCMOS output is off when TR is high. 

The MIC1555 may be used as an astable (oscillator) or monostable (one-shot) with separate threshold and trigger inputs. In the one-shot mode, the output pulse width is precisely controlled by an external resistor and a capacitor. Time delays may be accurately controlled from microseconds to hours. In the oscillator mode, the output is used to provide precise feedback, with a minimum of one resistor and one capacitor producing a 50% duty cycle square wave. 

The MIC1557 is designed for astable (oscillator) operation only, with a chip select/reset (CS) input for low power shutdown. One resistor and one capacitor provide a 50% duty cycle square wave. Other duty-cycle ratios may be produced using two diodes and two resistors. 

The MIC1555/7 is powered from a +2.7V to +18V supply voltage. 

The MIC1555/7 is available in the SOT-23-5 5-pin package, and is rated for –40°C to +85°C ambient temperature range 

## **Features** 

- +2.7V to +18V operation 

- Low current <1µA typical shutdown mode (MIC1557) 200µA typical (TRG and THR low) at 3V supply 

- Timing from microseconds to hours 

- “Zero” leakage trigger and threshold inputs 

- 50% square wave with one Resistor, one Capacitor 

- Threshold input precedence over trigger input 

- <15Ω output on resistance 

- No output cross-conduction current spikes 

- <0.005%/°C temperature stability 

- <0.055%/V supply stability 

- Small SOT-23-5 surface mount package 

## **Applications** 

- Precision timer 

- Pulse generation 

- Sequential timing 

- Time-delay generation 

- Missing pulse detector 

- Micropower oscillator to 5MHz 

- Charge-pump driver 

- LED blinker 

- Voltage converter 

- Linear sweep generator 

- Variable frequency and duty cycle oscillator 

- Isolated feedback for power supplies 

## **Typical Application** 

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+5V<br>100µs<br>MIC1555<br>1 3<br>VS OUT Output<br>StandbyTrigger 4 TRG 1k<br>2 5<br>GND THR<br>0.1µF<br>Monostable (One-Shot)<br>**----- End of picture text -----**<br>


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+5V<br>8kHz<br>MIC1557<br>4 5<br>VS OUT Output<br>DisabledEnabled 3 C S 1k<br>2 1<br>GND T/T<br>0.1µF<br>Astable (Oscillator)<br>**----- End of picture text -----**<br>


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 

M9999-072806 

July 2006 

MIC1555/1557 

Micrel, Inc. 

## **Ordering Information** 

|**ering Information**|**ering Information**|||||
|---|---|---|---|---|---|
|**Part Number**||**Marking**||**Temperature Range**|**Package**|
|**Standard**|**Pb-Free**|**Standard**|**Pb-Free**|||
|MIC1555BM5|MIC1555YM5|T10|T1<br>0|–40° to +85°C|5-Pin SOT-23|
|MIC1557BM5|MIC1557YM5|T11|T1<br>1|–40° to +85°C|5-Pin SOT-23|



**Note:** 

Under bar ( __ ) may not be to scale. 

## **Pin Configuration** 

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OUT GND VS<br>3 2 1<br>Part<br>Identification<br>T10<br>4 5<br>TRG THR<br>MIC1555<br>5-Pin SOT-23 (M)<br>**----- End of picture text -----**<br>


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CS GND T/T<br>3 2 1<br>Part<br>Identification<br>T11<br>4 5<br>VS OUT<br>MIC15557<br>5-Pin SOT-23 (M)<br>**----- End of picture text -----**<br>


## **Pin Description** 

|**Description**||||
|---|---|---|---|
|**Pin Number**<br>**MIC1555**|**Pin Number**<br>**MIC1557**|**Pin Name**|**Pin Name**|
|1|4|VS|Supply (Input):  +2.7 to +18V supply.|
|2|2|GND|Ground:  Supply return.|
||3|CS|Chip Select/Reset (Input):  Active high at >2/3VS.  Output off<br>when low at<1/3VS.|
|3|5|OUT|Output:  CMOS totem-pole output.|
|4||TRG|Trigger (Input):  Sets output high.  Active low (at ≤ 2/3VS<br>nominal).|
|5||THR|Threshold (Dominant Input):  Sets output low.  Active high (at<br>≥ 2/3VSnominal).|
||1|T/T|Trigger/Threshold (Input):  Internally connected to both<br>threshold and trigger functions.  See TRG and THR.|



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## **Absolute Maximum Ratings** 

## **Operating Ratings** 

|**Absolute Maximum Ratings**|**Operating Ratings**|
|---|---|
|Supply Voltage (VS)......................................................+22V|Supply voltage (VS) ....................................... +2.7V to +18V|
|Threshold Voltage (VTHR, VT/T). ....................................+22V|Ambient Temperature (TA) ..........................–40°C to +85°C|
|Trigger Voltage (VTGR, VT/T)..........................................+22V|Package Thermal Resistance|
|Lead Temperature (soldering, 10sec.)....................... 300°C|(θJA) .................................................................220°C/W|
||(θJC) .................................................................130°C/W|



## **Electrical Characteristics** 

## TA = 25°C, **bold** values indicate –40°C< TA < +85°C, unless noted. 

|**Parameter**|**Condition**|**Min**|**Typ**|**Max**|**Units**|
|---|---|---|---|---|---|
|Supply current|VS= 5V||240|**300**|µA|
||VS= 15V||350|**400**|µA|
|Monostable Timing Accuracy|RA= 10k, C =0.1µF, VS= 5V||2||%|
||RA= 10k, C =0.1µF, VS= 5V|**858**||**1161**|µs|
|Monostable Drift over Temp|VS= 5V, –55 ≤ TA≤ +125°C,**Note 1**||100||ppm/°C|
||VS= 10V, –55 ≤ TA≤ +125°C,**Note 1**||150||ppm/°C|
||VS= 15V, –55 ≤ TA≤ +125°C,**Note 1**||200||ppm/°C|
|Monostable Drift over Supply|VS= 5V to 15V,**Note 1**||0.5||%/V|
|Astable Timing Accuracy|RA= RB= 10k, C = 0.1µF, VS= 5V||2||%|
||RA= RB= 10k, C = 0.1µF, VS= 5V|**1717**||**2323**|µs|
|Maximum Astable Frequency|RT= 1k, CT= 47pF, VS= 8V||5||MHz|
|Astable Drift over Temp|VS= 5V, –55 ≤ TA≤ +125°C,**Note 1**||100||ppm/°C|
||VS= 10V, –55 ≤ TA≤ +125°C,**Note 1**||150||ppm/°C|
||VS= 15V, –55 ≤ TA≤ +125°C,**Note 1**||200||ppm/°C|
|Astable Drift over Supply|VS= 5V to 15V,**Note 1**||0.5||%/V|
|Threshold Voltage|VS= 15V|**61**|67|**72**|%/VS|
|Trigger Voltage|VS= 15V|**27**|32|**37**|%/VS|
|Trigger Current|VS= 15V|||**50**|nA|
|Threshold Current|VS= 15V|||**50**|nA|
|Chip Select|on > 2/3 VS|**50**|67|**72**|%/VS|
||off > 1/3 VS|**28**|33|**50**|%/VS|
|Output Voltage Drop|VS= 15V, ISINK= 20mA||0.3|**1.25**|V|
||VS= 5V, ISINK= 3.2mA||0.08|**0.5**|V|
||VS= 15V, ISOURCE= 20mA|**14.1**|14.7||V|
||VS= 5V, ISOURCE= 3.2mA|**3.8**|4.7||V|
|SupplyVoltage|functional operation,**Note 1**|**2.7**||**18**|V|
|Output Rise Time|RL= 10M, CL= 10pF, VS= 5V,**Note 1**||15||ns|
|Output Fall Time|RL= 10M, CL= 10pF, VS= 5V,**Note 1**||15||ns|



**General Note:** Devices are ESD protected, however handling precautions recommended. **Note 1** .  Not tested. 

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## **Typical Characteristics** (TA = 25°C, VIN = +5) 

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On Resistance<br>vs. Temperature<br>70<br>COO<br>60<br>HLEEPEET<br>eo 50 eePTT ETT TT<br>Poerrr rrr ry ey<br>40 pee |<br>30 SeSSeeeeeeeeeCOPESESSSRREEe=Cee eee<br>PCH 45<br>20<br>aS>>_PPT00eeeen<br>10<br>SERRSEESREEEEs<br>0 POPE EET Ere<br>-40 Seestantastae -20 0 20 40 60 80 100<br>TEMPERATURE (°C)<br>)<br>(<br>E<br>C<br>N<br>A<br>T<br>SSI<br>E<br>R<br>N<br>O<br>**----- End of picture text -----**<br>


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k Factors<br>Times RC<br>2.0<br>1.9 -— HH<br>1.8<br>erase eee<br>1.7<br>1.6 em sect ee f=1k1 RC<br>1.5 SSPs ae1<br>1.4 PH en<br>1.3<br>1.2 eee eee t=k2 RC<br>= o<br>1.1 =a<br>eee<br>1.0 Peet<br>10 100 1000<br>RC (µs)<br>R<br>O<br>T<br>C<br>A<br>F<br>k<br>**----- End of picture text -----**<br>


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MIC1557 Chip Select<br>vs. Supply Voltage<br>14 persed<br>12<br>FeasanPeopseeekarascearseredtdcra|es erepa<br>10 ON<br>EEE...se sHEE caer He RESsEeer EE ED<br>8<br>HGFeetSEE<br>6<br>ecsitubeig”[TT [|<br>4 PeepBEES [|ere TT TC<br>2 Eek) [ery> CLT OFF |<br>Moto |<br>0 SeeeeeeeeT eeeCo<br>3 6 9 12 15 18<br>SUPPLY VOLTAGE (V)<br>)(V<br>E<br>G<br>A<br>T<br>L<br>O<br>V<br>T<br>C<br>E<br>L<br>E<br>S<br>PIH<br>C<br>**----- End of picture text -----**<br>


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Micrel, Inc. 

## **Functional Diagram** 

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VSUPPLY<br>VS<br>MIC1555<br>Bias<br>THR<br>100µs<br>S<br>Q<br>OUT Output<br>R<br>Standby<br>Trigger<br><100µs TRG<br>GND 1k<br>0.1µF<br>**----- End of picture text -----**<br>


**MIC1555 Block Diagram with External Components (Monostable Configuration)** 

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VSUPPLY<br>VS<br>1M MIC1557<br>C S Bias<br>8kHz<br>S<br>Q<br>OUT Output<br>R<br>T/T<br>GND 1k<br>0.1µF<br>**----- End of picture text -----**<br>


**MIC1557 Block Diagram with External Components (Astable Configuration)** 

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MIC1555/1557 

Micrel, Inc. 

## **Functional Description** 

Refer to the block diagrams. 

The MIC1555/7 provides the logic for creating simple RC timer or oscillator circuits. 

The MIC1555 has separate THR (threshold) and TRG (trigger) connections for monostable (one-shot) or astable (oscillator) operation. 

The MIC1557 has a single T/T (threshold and trigger) connection for astable (oscillator) operation only. The MIC1557 includes a CS (chip select/reset) control. 

## **Supply** 

VS (supply) is rated for +2.7V to +18V. An external capacitor is recommended to decouple noise. 

## **Resistive Divider** 

The resistive voltage divider is constructed of three equal value resistors to produce 1/3VS and 2/3VS voltage for trigger and threshold reference voltages. 

## **Chip Select/Reset (MIC1557 only)** 

CS (chip select/reset) controls the bias supply to the oscillator’s internal circuitry. CS must be connected to CMOS logic-high or logic-low levels. Floating CS will result in unpredictable operation. When the chip is deselected, the supply current is less than 1µA. Forcing CS low resets the MIC1557 by setting the flip flop, forcing the output low. 

## **Threshold Comparator** 

The threshold comparator is connected to S (set) on the RS flip-flop. When the threshold voltage (2/3VS) is reached, the flip-flop is set, making the output low. THR is dominant over TRG. 

## **Trigger Comparator** 

The trigger comparator is connected to R (reset) on the RS flip-flop. When TRG (trigger) goes below the trigger voltage (1/3VS), the flip-flop resets, making the output high. 

## **Flip-Flop and Output** 

A reset signal causes Q to go low, turning on the P- channel MOSFET and turning off the N-channel MOSFET.  This makes the output rise to nearly VS. 

A set signal causes Q to go high, turning off the P- channel MOSFET, and turning on the N-channel MOSFET, grounding OUT. 

## **Basic Monostable Operation** 

Refer to the MIC1555 functional diagram. 

A momentary low signal applied to TRG causes the output to go high. The external capacitor charges slowly through the external resistor. When VTHR (threshold voltage) reaches 2/3VS, the output is switched off, discharging the capacitor. During power-on, a single pulse may be generated. 

## **Basic Astable Operation** 

Refer to the MIC1557 functional diagram. 

The MIC1557 starts with T/T low, causing the output to go high. The external capacitor charges slowly through the external resistor. When VT/T reaches 2/3VS (threshold voltage), the output is switched off, slowly discharging the capacitor. When VT/T decreases to 1/3VS (trigger voltage), the output is switched on, causing VT/T to rise again, repeating the cycle. 

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MIC1555/1557 

Micrel, Inc. 

## **Application Information** 

## **Basic Monostable (One-Shot) Circuit** 

A monostable oscillator produces a single pulse each time that it is triggered, and is often referred to as a “one-shot”. The pulse width is constant, while the time between pulses depends on the trigger input. One-shots are generally used to “stretch” incoming pulses, of varying widths, to a fixed width. The IttyBitty MIC1555 is designed for monostable operation, but may also be connected to provide astable oscillations. The pulse width is determined by the time it takes to charge a capacitor from ground to a comparator trip point. If the capacitor (CT) is charged through a resistor (RT) connected to the output of an MIC1555, the trip point is approximately 1.1RCT (the same time as the initial power-on cycle of an astable circuit.) If the trigger pulse of an MIC1555 remains low longer than the output pulse width, short oscillations may be seen in the output of a one-shot circuit, since the threshold pin has precedence over the trigger pin. These occur since the output goes low when the threshold is exceeded, and then goes high again as the trigger function is asserted. AC coupling the input with a series capacitor and a pull-up resistor, with an RC time constant less than the pulse width, will prevent these short oscillations. A diode (DT) in parallel with (RT) resets the one-shot quickly. 

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2.7V to 18V<br>RT<br>DT VS 1<br>RPU THR tON = 1.1RT CT<br>5 C S<br>Trigger CIN TRG OUT OUT<br>3<br>1 3VS 4<br>CT<br>MIC1555<br>GND 2<br>**----- End of picture text -----**<br>


**Figure 1.  One-Shot Diagram** 

The period of a monostable circuit is: 

t = k2 RC 

where: 

t = period (s) 

k2 = constant [from Typical Characteristics graph] 

R = resistance (Ω) 

C = capacitance (F) 

## **Basic Astable (Oscillator) Circuits** 

An astable oscillator switches between two states, “on” and “off”, producing a continuous square wave. The IttyBitty MIC1557 is optimized for this function, with the two comparator inputs, threshold and trigger (T/T), tied together internally. Chip select (CS) is brought out to allow on-off control of the oscillator. 

The MIC1555 may also be used as an astable oscillator by tying the threshold and trigger pins together, forming a T/T pin. If a resistor (RT) is connected from the output to a grounded timing capacitor, (CT) the voltage at their junction will ramp up from ground when the output goes high. If the T/T pin is connected to this junction, the output will switch low when the ramp exceeds 2/3 of the input voltage. The junction's voltage ramps down toward ground while the output is low. When the ramp is below 1/3 of the input voltage, the output switches to high, and the junction ramps up again. The continuing frequency of an MIC1555/7 astable oscillator depends on the RC time constant, and is approximately 0.7/RC below 1MHz. At frequencies above 1MHz the RC multiplier increases as capacitance is decreased, and propagation delay becomes dominant. Non-symmetrical oscillator operation is possible at frequencies up to 5MHz. 

If a duty cycle other than 50% is desired, a low-power signal diode may be connected in series with the timing resistor (RA), and a second resistor (RB) in series with an opposite facing diode connected in parallel. The frequency is then made up of two components, the charging time (tA) and the discharging time (tB) tA= 0.7RAC and tB= 0.7RBC. The frequency is the reciprocal of the sum of the two times tA + tB, so the total time is 1.4RTCT. The first half-cycle of an astable, after poweron or CS enable, is lengthened since the capacitor is charging from ground instead of the 1/3 input trigger trip voltage, to 1.1RC, the same as a monostable pulse. 

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2.7V to 18V<br>CB<br>VS 4<br>RE<br>T/T<br>C S<br>1 C S 3<br>t<br>OUT<br>OUT<br>5<br>t = 0.7(RA+RB)CT<br>MIC1557<br>RA GND 2<br>1k to 1M<br>RB<br>CT<br>100pF to 10µF<br>**----- End of picture text -----**<br>


**Figure 2.  Oscillator Diagram** 

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The MIC1555 or MIC1557 can be used to construct an oscillator. 

The frequency of an astable oscillator is: 

**==> picture [42 x 25] intentionally omitted <==**

where: 

f = frequency (Hz) k1 = constant [from Typical Characteristics graph] 

- R = resistance (Ω) 

- C = capacitance (F) 

To use the MIC1555 as an oscillator, connect TRG to THR. 

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+5V<br>8kHz<br>MIC1555<br>1 3<br>VS OUT Output<br>4 TRG 1k<br>2 GND THR 5<br>0.1µF<br>**----- End of picture text -----**<br>


**Figure 3.  MIC1555 Oscillator Configuration** 

The MIC1557 features a CS input. When logic-low, CS places the MIC1557 into a <1µA shutdown state. If unused, the MIC1557 CS input on must be pulled up. 

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+5V 8kHz<br>MIC1557<br>4 5<br>VS OUT Output<br>1M 3 C S 1k<br>2 GND T/T 1<br>0.1µF<br>**----- End of picture text -----**<br>


**Figure 4.  MIC1557 Oscillator Configuration** 

## **Falling-Edge Triggered Monostable Circuit** 

The MIC1555 may be triggered by an ac-coupled fallingedge, as shown in figure 5. The RC time constant of the input capacitor and pull-up resistor should be less than the output pulse time, to prevent multiple output pulses. A diode across the timing resistor provides a fast reset at the end of the positive timing pulse. 

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+5V 100µs<br>MIC1555<br>1M 1 3<br>VS OUT Output<br>Input 4 TRG 1k 1N4148<br>2 5<br>GND THR<br>0.1µF<br>**----- End of picture text -----**<br>


## **Rising-Edge Triggered Monostable Circuit** 

The MIC1555 may be triggered by an ac-coupled risingedge, as shown in figure 6. The pulse begins when the ac-coupled input rises, and a diode from the output holds the THR input low until TRG discharges to 1/3VS. This circuit provides a low-going output pulse. 

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+5V<br>100µs<br>MIC1555<br>1 3<br>VS OUT Output<br>4 TRG 1k 1N4148<br>2 GND THR 5 Input<br>0.1µF<br>**----- End of picture text -----**<br>


**Figure 6.  Rising-Edge Trigger Configuration** 

## **Accuracy** 

The two comparators in the MIC1555/7 use a resistor voltage divider to set the threshold and trigger trip points to approximately 2/3 and 1/3 of the input voltage, respectively. Since the charge and discharge rates of an RC circuit are dependent on the applied voltage, the timing remains constant if the input voltage varies. If a duty cycle of exactly 50% (or any other value from 1 to 99%), two resistors (or a variable resistor) and two diodes are needed to vary the charge and discharge times. The forward voltage of diodes varies with temperature, so some change in frequency will be seen with temperature extremes, but the duty cycle should track. For absolute timing accuracy, the MIC1555/7 output could be used to control constant current sources to linearly charge and discharge the capacitor, at the expense of added components and board space. 

## **Long Time Delays** 

Timing resistors larger than 1MΩ or capacitors larger than 10µF are not recommended due to leakage current inaccuracies. Time delays greater than 10 seconds are more accurately produced by dividing the output of an oscillator by a chain of flip-flop counter stages. To produce an accurate one-hour delay, for example, divide an 4.55Hz MIC1557 oscillator by 16,384 (4000hex, 214) using a CD4020 CMOS divider. 4.5Hz may be generated with a 1µF CT and approximately 156kΩ. 

## **Inverting Schmitt Trigger** 

**Figure 5.  Falling-Edge Trigger Configuration** 

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+12V 

MOSFET may be driven by a second MIC1555/7, powered by 12V to 15V, to level-shift the input. 

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+5V +12V<br>OFF  3.3V MIC1555<br>5 THR VS 1 RL<br>4<br>ON  1.6V TRG<br>2 GND OUT 3<br>**----- End of picture text -----**<br>


**Figure 7.  Schmitter Trigger** 

## **Charge-Pump Low-Side MOSFET Drivers** 

A standard MOSFET requires approximately 15V to fully enhance the gate for minimum RDS(on). Substituting a logic-level MOSFET reduces the required gate voltage, allowing an MIC1557 to be used as an inverting Schmitt Trigger, described above. An MIC1557 may be configured as a voltage quadrupler to boost a 5V input to over 15V to fully enhance an N-channel MOSFET which may have its drain connected to a higher voltage, through a high-side load. ATTL high signal applied to CS enables a 10kHz oscillator, which quickly develops 15V at the gate of the MOSFET, clamped by a zener diode. A resistor from the gate to ground ensures that the FET will turn off quickly when the MIC1557 is turned off. 

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N-Channel<br>MOSFET RL<br>TTL High = ON (IRF540)<br>+5V 15V<br>MIC1557<br>4 3<br>VS C S<br>1<br>T/T<br>C1 2 GND OUT 5<br>100pF RE<br>to 10µF 100k<br>RT 1k to 1M<br>**----- End of picture text -----**<br>


**Figure 8.  Charge-Pump** 

## **Audible Voltmeter** 

If an additional charge or discharge source is connected to the timing capacitor, the frequency may be shifted by turning the source on or off. An MIC1555 oscillator, powered by the circuit under test, may be used to drive a small loud speaker or piezo-electric transducer to provide a medium frequency for an open or high impedance state at the probe. A high tone is generated for a high level, and a lower frequency for a logic low on the probe. 

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RT 10k +5V to +18V<br>MIC1555<br>1N914 5 1<br>THR VS<br>47k 4 0.001µF<br>TRG<br>10k CT 2 GND OUT 3 10k<br>0.01µF<br>100<br>**----- End of picture text -----**<br>


**Figure 9.  Audible Voltmeter** 

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## **Package Information** 

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**5-Pin SOT-23 (M)** 

## **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 

The 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 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. 

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