Overview
The UC3845DG4 is a current-mode PWM controller from Texas Instruments, part of the UCx84x family. This integrated circuit is designed to implement off-line and DC-to-DC fixed-frequency current-mode control schemes with a minimal number of external components. It features a low start-up current of less than 1 mA, automatic feedforward compensation, pulse-by-pulse current limiting, and enhanced load-response characteristics. The device includes an undervoltage lockout (UVLO) with hysteresis, double-pulse suppression, and a high-current totem-pole output stage suitable for driving N-channel MOSFETs.
Key Specifications
| Parameter | Min | Typ | Max | Unit |
|---|---|---|---|---|
| VCC (Low impedance source) | - | - | 30 | V |
| IVCC (Self Limiting) | - | - | 30 mA | mA |
| VFB and VISENSE (Analog input voltage) | -0.3 | - | 6.3 | V |
| IOUTPUT (Output drive current) | - | - | ±1 A | A |
| ICOMP (Error amplifier output sink current) | - | - | 10 mA | mA |
| EOUTPUT (Output energy, capacitive load) | - | - | 5 µJ | µJ |
| TJ (Junction temperature) | - | - | 150 °C | °C |
| Tstg (Storage temperature) | -65 | - | 150 °C | °C |
| TA (Operating free-air temperature) | 0 | - | 70 °C | °C |
| fOSC (Oscillator frequency) | 100 kHz | - | 500 kHz | kHz |
| VVREF (Reference voltage) | 4.9 V | 5 V | 5.1 V | V |
| VCCON (UVLO enable threshold) | 14.5 V | 16 V | 17.5 V | V |
| VCCOFF (UVLO off threshold) | 8.5 V | 10 V | 11.5 V | V |
| DMAX (Maximum duty cycle) | 47% | 48% | 50% | % |
Key Features
- Optimized for off-line and DC-to-DC converters
- Low start-up current (< 1 mA)
- Automatic feedforward compensation
- Pulse-by-pulse current limiting
- Enhanced load-response characteristics
- Undervoltage lockout with hysteresis
- Double-pulse suppression
- High-current totem-pole output stage
- Internally trimmed bandgap reference
- Up to 500-kHz operation
- Error amplifier with low output resistance
Applications
- Switching regulators of any polarity
- Transformer-coupled DC-DC converters
Q & A
- What is the operating temperature range for the UC3845DG4?
The UC3845DG4 operates from 0°C to 70°C.
- What is the maximum duty cycle for the UC3845DG4?
The maximum duty cycle for the UC3845DG4 is up to 50%.
- What is the purpose of the undervoltage lockout (UVLO) feature?
The UVLO feature ensures the device does not operate below a certain voltage threshold, preventing damage and ensuring stable operation.
- How is the oscillator frequency set in the UC3845DG4?
The oscillator frequency can be set using the timing resistor (RRT) and timing capacitor (CCT) connected to the RT/CT pin, with the frequency estimated by the equation fOSC = 1.72 / (RRT × CCT).
- What is the reference voltage provided by the UC3845DG4?
The UC3845DG4 provides a 5-V reference voltage with a tolerance of 4.9 V to 5.1 V.
- What type of output stage does the UC3845DG4 have?
The UC3845DG4 has a high-current totem-pole output stage suitable for driving N-channel MOSFETs.
- What is the maximum output drive current of the UC3845DG4?
The maximum output drive current of the UC3845DG4 is ±1 A.
- What are the package options available for the UC3845DG4?
The UC3845DG4 is available in SOIC (8-pin and 14-pin), PDIP (8-pin), and CFP (8-pin) packages.
- How does the error amplifier in the UC3845DG4 contribute to the device's functionality?
The error amplifier provides low output resistance and is used to control the power converter voltage-feedback loop for stability.
- What is the purpose of the double-pulse suppression feature in the UC3845DG4?
The double-pulse suppression feature prevents the output from generating two pulses in a single switching cycle, ensuring reliable operation.
