# NE555

Precision timer IC for monostable, astable, and bistable timing circuits

| Field | Value |
|-------|-------|
| Manufacturer | Texas Instruments |
| Package | PDIP-8 |
| Pins | 8 |
| Datasheet | [PDF](https://www.ti.com/lit/ds/symlink/ne555.pdf) |

## Pin Table

| # | Name | Type | Group | Description |
|---|------|------|-------|-------------|
| 1 | GND | power_in | POWER | Ground reference. Connect to circuit ground plane with short, low-impedance trace. |
| 8 | VCC | power_in | POWER | Positive supply voltage input. Operating range 4.5V to 16V. Bypass with 100nF ceramic capacitor close to pin. |
| 2 | TRIG | input | TIMING | Trigger input. A negative pulse below 1/3 VCC initiates the timing cycle and sets the output high. Input impedance is... |
| 6 | THRES | input | TIMING | Threshold input. When voltage exceeds 2/3 VCC, the timing cycle ends and the output goes low. Typically connected to ... |
| 7 | DISCH | output | TIMING | Discharge output. Open-collector transistor output that discharges the external timing capacitor when the output goes... |
| 3 | OUT | output | OUTPUT | Timer output. Drives high (near VCC) or low (near GND) with up to 200mA sink/source capability. Rise and fall times a... |
| 4 | RESET | input | CONTROL | Active-low reset input. Pulling below 0.7V forces output low and overrides all other inputs. Tie to VCC through a 10k... |
| 5 | CTRL | input | CONTROL | Control voltage input. Provides direct access to the internal 2/3 VCC comparator reference. Bypass with 10nF capacito... |

## Pin Groups

### POWER

Supply pins. VCC accepts 4.5V–16V. Bypass VCC with 100nF ceramic close to the pin. GND is the reference for all internal comparators and the output stage.

### TIMING

Timing network interface. TRIG starts the cycle (falling edge below 1/3 VCC), THRES ends it (rising above 2/3 VCC), and DISCH resets the external RC capacitor. Together they set the output pulse width: t = 1.1 × R × C.

### OUTPUT

Push-pull output capable of sourcing or sinking up to 200mA. Drives TTL and CMOS loads directly. Output swings within ~1.5V of each rail.

### CONTROL

RESET overrides all timing and forces output low. CTRL provides access to the internal voltage divider reference (2/3 VCC) for modulation or improved noise rejection.

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