Overview
The UC3845BD from onsemi is a high-performance, fixed-frequency current-mode PWM (Pulse Width Modulation) controller. It is specifically designed for off-line and DC-to-DC converter applications, offering a cost-effective solution with minimal external components. This integrated circuit features a trimmed oscillator for precise duty cycle control, a temperature-compensated reference, a high-gain error amplifier, a current sensing comparator, and a high-current totem pole output ideal for driving power MOSFETs.
The UC3845BD is part of the UC3844B/UC3845B series, which includes protective features such as input and reference undervoltage lockouts with hysteresis, cycle-by-cycle current limiting, and a flip-flop that allows output deadtimes to be programmed from 50% to 70%.
Key Specifications
| Parameter | Symbol | Value | Unit |
|---|---|---|---|
| Supply Voltage | VCC | 30 | V |
| Output Current | IO | ±1 | A |
| Analog Inputs (Pin 2, 3) | V(ANA) | -0.3 to 6.3 | V |
| Error Amp Output Sink Current | ISINK (E.A) | 10 | mA |
| Power Dissipation at TA≤25°C (14SOP) | PD | 680 | mW |
| Storage Temperature Range | TSTG | -65 ~ +150 | °C |
| Oscillation Frequency | f | 47 to 57 | kHz |
| UVLO Turn-On Threshold | 8.5 | V | |
| UVLO Turn-Off Threshold | 7.6 | V | |
| Maximum Operating Supply Voltage | VCC | 36 | V |
| Switching Frequency | Up to 500 kHz |
Key Features
- Trimmed oscillator for precise duty cycle control
- Temperature-compensated reference
- High-gain error amplifier
- Current sensing comparator
- High-current totem pole output for driving power MOSFETs
- Undervoltage lockout with hysteresis
- Low startup and operating current
- Output deadtime adjustable from 50% to 70%
- Automatic feed-forward compensation
- Latching PWM for cycle-by-cycle current limiting
- Pb-free packages available and RoHS compliant
Applications
The UC3845BD is designed for use in off-line and DC-to-DC converter applications. It is particularly suited for:
- Off-line power supplies
- DC-to-DC converters
- Switch-mode power supplies
- High-efficiency power conversion systems
Q & A
- What is the primary function of the UC3845BD?
The UC3845BD is a fixed-frequency current-mode PWM controller designed for off-line and DC-to-DC converter applications.
- What are the UVLO thresholds for the UC3845BD?
The UVLO thresholds for the UC3845BD are 8.5V (on) and 7.6V (off).
- What is the maximum operating supply voltage for the UC3845BD?
The maximum operating supply voltage for the UC3845BD is 36V.
- What is the switching frequency range of the UC3845BD?
The switching frequency of the UC3845BD can go up to 500 kHz.
- What type of output does the UC3845BD have?
The UC3845BD has a high-current totem pole output suitable for driving power MOSFETs.
- What protective features does the UC3845BD include?
The UC3845BD includes protective features such as input and reference undervoltage lockouts with hysteresis, cycle-by-cycle current limiting, and a flip-flop for adjustable output deadtimes.
- What are the available package types for the UC3845BD?
The UC3845BD is available in 8-pin dual-in-line, 8-pin surface mount (SO-8), and 14-pin surface mount (SO-14) packages).
- Is the UC3845BD RoHS compliant?
Yes, the UC3845BD is Pb-free and RoHS compliant).
- What is the storage temperature range for the UC3845BD?
The storage temperature range for the UC3845BD is -65°C to +150°C).
- How is the oscillator frequency programmed in the UC3845BD?
The oscillator frequency is programmed by the values selected for the timing components RT and CT).
