The UC3845BD1R2G is the SOIC-8 tape-and-reel version of the UC3845B, a member of onsemi's industry-standard UC3842B/3843B/3844B/3845B high-performance current-mode controller family. These controllers are specifically designed for off-line switch-mode power supplies and DC-DC converter applications, delivering a complete PWM control solution with a minimal count of external components.

On chip it integrates a trimmed oscillator for precise frequency control, a temperature-compensated voltage reference, a high-gain error amplifier, a current-sensing comparator and a high-current totem-pole output stage ideally suited for driving a power MOSFET directly. Current-mode operation provides automatic feed-forward compensation and inherently fast response to input voltage changes, while the latching PWM performs cycle-by-cycle current limiting for robust overload behavior.

Within the family, the UC3845B variant pairs a low 8.5V (on) / 7.6V (off) undervoltage lockout with an internal flip-flop that clamps the maximum duty cycle to 50%. Protection features further include UVLO with hysteresis, programmable output deadtime and low startup and operating current. The oscillator frequency is guaranteed at 250kHz and current-mode operation extends to 500kHz. The D1 suffix denotes the 8-pin SOIC (CASE 751) and the R2G suffix tape-and-reel, Pb-free packing.

Note: Refer to the official onsemi UC3844B/UC3845B datasheet for full electrical parameters and curves. Subject to change without notice; verify all parameters before final design.

The UC3845BD1R2G comes in the 8-pin narrow-body SOIC-8 surface-mount package, onsemi CASE 751, identified by the D1 suffix. The family is also offered in PDIP-8 (N suffix, CASE 626) for through-hole assembly and in SOIC-14 (D suffix), which separates power and ground of the totem-pole output stage onto dedicated pins.

The R2G ordering suffix indicates tape-and-reel packing with Pb-free terminations, RoHS compliant and compatible with standard SOIC-8 land patterns and reflow profiles for automated SMT assembly.

The UC3845BD1R2G uses the industry-standard 8-pin current-mode controller pinout (top view):

• Pin 1 - COMP: Error-amplifier output / loop compensation.
• Pin 2 - VFB: Voltage feedback, inverting input of the error amplifier.
• Pin 3 - CS (Current Sense): Switch-current sense input for the PWM comparator and cycle-by-cycle limit.
• Pin 4 - RT/CT: Oscillator timing resistor and capacitor.
• Pin 5 - GND: Ground.
• Pin 6 - OUTPUT: Totem-pole gate-drive output.
• Pin 7 - VCC: Supply voltage (UVLO 8.5V on / 7.6V off).
• Pin 8 - VREF: Trimmed reference output.

Decouple VCC and VREF to ground with ceramic capacitors close to the device, and keep the CS and RT/CT traces short. Confirm the exact pin assignment against the datasheet image below before layout.

The following UC384x family controllers are listed for reference. Verify UVLO thresholds, maximum duty cycle, temperature grade and package before substituting.

onsemi (ON Semiconductor, NASDAQ: ON), headquartered in Scottsdale, Arizona, USA, is a leading supplier of power and analog semiconductors. The UC384xB current-mode controller family - inherited through Fairchild Semiconductor - is one of the longest-serving industry standards in switch-mode power supply design, with decades of field history, extensive application literature and an automotive-qualified NCV prefix option.

onsemi provides complete datasheets, design notes and long-term supply for the family, with authorized distribution and technical support across China for both prototype and volume requirements.