component
UC3845BD1
Public Made by Adomby adom
STMicroelectronics DC-DC Converters, SO-8. Pinout cross-checked by two models against the datasheet, KiCad symbol/footprint/3D.
3D Model
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Symbol & Footprint
Schematic Symbol
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PCB Footprint
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Datasheet
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README
markdownUC3845BD1
STMicroelectronics · DC-DC Converters · SO-8
UC3845BD1 from STMicroelectronics, in a SO-8. Pinout and pin descriptions extracted from the manufacturer datasheet (extract_pins, cross-checked by a second model); symbol, footprint, and 3D from KiCad-official CAD.
Pinout
| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | COMP | output | Error amplifier output made available for loop compensation. |
| 2 | VFB | input | Inverting input of the error amplifier, normally connected to the power supply output through a resistor divider (analog input range -0.3 to 5.5 V). |
| 3 | ISENSE | input | Current sense input where a voltage proportional to inductor current is applied so the PWM can terminate output switch conduction (analog input range -0.3 to 5.5 V). |
| 4 | RT/CT | passive | Oscillator frequency and maximum output duty cycle are set by resistor RT to Vref and capacitor CT to ground, with operation to 500kHz possible. |
| 5 | GROUND | power_in | Combined control circuitry and power ground. |
| 6 | OUTPUT | output | Totem-pole output that directly drives the gate of a power MOSFET, sourcing and sinking peak currents up to 1A. |
| 7 | VCC | power_in | Positive supply of the control IC (30V maximum from a low impedance source). |
| 8 | Vref | power_out | 5V reference output (up to 50mA) that provides charging current for capacitor CT through resistor RT. |
Key specifications
| Parameter | Value |
|---|---|
| Manufacturer | STMicroelectronics |
| Package | SO-8 |
| Category | Power Management ICs |
| Pins | 8 |
Electrical characteristics
Limits as printed in the datasheet (page.json metadata.characteristics carries them as data).
| Parameter | Symbol | Min | Typ | Max | Unit | Conditions | Page |
|---|---|---|---|---|---|---|---|
| Supply Voltage (low impedance source) | Vi | 30 | V | low impedance source | 2 | ||
| Output Current | IO | -1 | 1 | A | 2 | ||
| Output Energy (capacitive load) | EO | 5 | µJ | 2 | |||
| Analog Inputs (pins 2, 3) | -0.3 | 5.5 | V | pins 2, 3 | 2 | ||
| Error Amplifier Output Sink Current | 10 | mA | 2 | ||||
| Power Dissipation (SO8) | Ptot | 800 | mW | Tamb ≤ 25 °C (SO8) | 2 | ||
| Storage Temperature Range | Tstg | -65 | 150 | °C | 2 | ||
| Junction Operating Temperature | TJ | -40 | 150 | °C | 2 | ||
| Lead Temperature (soldering 10s) | TL | 300 | °C | soldering 10s | 2 | ||
| Thermal Resistance Junction-ambient | Rth j-amb | 150 | °C/W | SO8, max. | 3 | ||
| Reference Output Voltage | VREF | 4.9 | 5 | 5.1 | V | Tj = 25°C Io = 1mA | 3 |
| Line Regulation | ΔVREF | 2 | 20 | mV | 12V ≤ Vi ≤ 25V | 3 | |
| Load Regulation | ΔVREF | 3 | 25 | mV | 1 ≤ Io ≤ 20mA | 3 | |
| Temperature Stability | ΔVREF/ΔT | 0.2 | mV/°C | Note 2 | 3 | ||
| Total Output Variation | VREF | 4.82 | 5.18 | V | Line, Load, Temperature | 3 | |
| Output Noise Voltage | eN | 50 | µV | 10Hz ≤ f ≤ 10KHz Tj = 25°C (note 2) | 3 | ||
| Long Term Stability | 5 | 25 | mV | Tamb = 125°C, 1000Hrs (note 2) | 3 | ||
| Output Short Circuit | ISC | -30 | -100 | -180 | mA | 3 | |
| Oscillator Frequency | fOSC | 49 | 52 | 55 | KHz | Tj = 25°C | 3 |
| Oscillator Frequency | fOSC | 48 | 56 | KHz | TA = Tlow to Thigh | 3 | |
| Oscillator Frequency | fOSC | 225 | 250 | 275 | KHz | TJ = 25°C (RT = 6.2k, CT = 1nF) | 3 |
| Frequency Change with Voltage | ΔfOSC/ΔV | 0.2 | 1 | % | VCC = 12V to 25V | 3 | |
| Frequency Change with Temp. | ΔfOSC/ΔT | 0.5 | % | TA = Tlow to Thigh | 3 | ||
| Oscillator Voltage Swing (peak to peak) | VOSC | 1.6 | V | 3 | |||
| Discharge Current | Idischg | 7.8 | 8.3 | 8.8 | mA | VOSC =2V, TJ = 25°C | 3 |
| Discharge Current | Idischg | 7.6 | 8.8 | mA | VOSC =2V, TA = Tlow to Thigh | 3 | |
| Error Amp Input Voltage | V2 | 2.42 | 2.5 | 2.58 | V | VPIN1 = 2.5V | 3 |
| Error Amp Input Bias Current | Ib | -0.1 | -2 | µA | VFB = 5V | 3 | |
| Open Loop Voltage Gain | AVOL | 65 | 90 | dB | 2V ≤ Vo ≤ 4V | 3 | |
| Unity Gain Bandwidth | BW | 0.7 | 1 | MHz | TJ = 25°C | 3 | |
| Power Supply Rejection Ratio | PSRR | 60 | 70 | dB | 12V ≤ Vi ≤ 25V | 3 | |
| Error Amp Output Sink Current | Io | 2 | 12 | mA | VPIN2 = 2.7V VPIN1 = 1.1V | 3 | |
| Error Amp Output Source Current | Io | -0.5 | -1 | mA | VPIN2 = 2.3V VPIN1 = 5V | 3 | |
| Error Amp VOUT High | VOUT | 5 | 6.2 | V | VPIN2 = 2.3V; RL = 15KΩ to Ground | 3 | |
| Error Amp VOUT Low | VOUT | 0.8 | 1.1 | V | VPIN2 = 2.7V; RL = 15KΩ to Pin 8 | 3 | |
| Current Sense Gain | GV | 2.85 | 3 | 3.15 | V/V | note 3 & 4 | 3 |
| Maximum Input Signal | V3 | 0.9 | 1 | 1.1 | V | VPIN1 = 5V (note 3) | 3 |
| Supply Voltage Rejection | SVR | 70 | dB | 12 ≤ Vi ≤ 25V (note 3) | 3 | ||
| Current Sense Input Bias Current | Ib | -2 | -10 | µA | 3 | ||
| Delay to Output | 150 | 300 | ns | 3 | |||
| Output Low Level | VOL | 0.1 | 0.4 | V | ISINK = 20mA | 4 | |
| Output Low Level | VOL | 1.6 | 2.2 | V | ISINK = 200mA | 4 | |
| Output High Level | VOH | 13 | 13.5 | V | ISOURCE = 20mA | 4 | |
| Output High Level | VOH | 12 | 13.5 | V | ISOURCE = 200mA | 4 | |
| UVLO Saturation | VOLS | 0.1 | 1.1 | V | VCC = 6V; ISINK = 1mA | 4 | |
| Rise Time | tr | 50 | 150 | ns | Tj = 25°C CL = 1nF (2) | 4 | |
| Fall Time | tf | 50 | 150 | ns | Tj = 25°C CL = 1nF (2) | 4 | |
| Start Threshold | 7.8 | 8.4 | 9 | V | X843B/5B | 4 | |
| Min Operating Voltage After Turn-on | 7 | 7.6 | 8.2 | V | X843B/5B | 4 | |
| Maximum Duty Cycle | 47 | 48 | 50 | % | X844B/5B | 4 | |
| Minimum Duty Cycle | 0 | % | 4 | ||||
| Start-up Current | Ist | 0.3 | 0.5 | mA | Vi = 6.5V for UCX843B/45B | 4 | |
| Operating Supply Current | Ii | 12 | 17 | mA | VPIN2 = VPIN3 = 0V | 4 | |
| Zener Voltage | Viz | 30 | 36 | V | Ii = 25mA | 4 | |
| Operating Ambient Temperature | Tamb | 0 | 70 | °C | UC384XB | 3 |
CAD (KiCad official)
- Symbol:
UC3845BD1 - Footprint:
Package_SO:SOIC-8_3.9x4.9mm_P1.27mm - 3D model: SO-8 (KiCad packages3D, STEP)
- 3D model files:
uc3845bd1-etched.step/uc3845bd1-etched.glbcarry the MPN laser-etched on the die in a toggleableAdom.LaserEtchgroup (Fusion-ready);uc3845bd1.step/uc3845bd1.glbare the bare package body.
Provenance
Data extracted from the manufacturer datasheet, not a distributor listing:
- Datasheet: STMicroelectronics datasheet (15 pp, sha256
fedfd7362400f8b3, retrieved 2026-10-23, tier: lcsc) - Extractor: parts-factory
2.0.0/extract_pins 0.3, primaryclaude-sonnet-5-5(text), consensusclaude-sonnet-5-5(agreed), guards: pin_guards 0.1: passed. Pins are checked against the footprint pad set and their cited datasheet pages before publish. - CAD: KiCad official libraries (CC-BY-SA 4.0).