The UC3843BD1013TR from STMicroelectronics is a high-performance fixed-frequency current-mode PWM controller designed for offline and DC-DC switching-power applications with a minimal external component count. It integrates a trimmed oscillator, error amplifier, PWM comparator, current-limit circuitry, undervoltage lockout, and a high-current totem-pole output stage.
The oscillator frequency is programmed using external RT and CT components, supporting current-mode operation up to 500kHz with oscillator performance guaranteed at 250kHz. Unlike the UC3844B and UC3845B, the UC3843B does not blank every second clock cycle, allowing a typical maximum duty cycle of 96% and operation approaching 100%.
The controller uses low-voltage undervoltage-lockout thresholds, with a typical start threshold of 8.4V and a specified range from 7.8V to 9.0V. After startup, the typical minimum operating voltage is 7.6V. The output is held low while the device is in undervoltage lockout.
Typical startup current is only 0.3mA, with a specified maximum of 0.5mA. Typical operating supply current is 12mA, with a maximum of 17mA. The low startup-current requirement helps reduce dissipation in offline startup networks.
Its high-current totem-pole output directly drives an external N-channel power MOSFET and supports peak source and sink currents of up to ±1A. With a 1nF load, typical output rise and fall times are both 50ns, supporting fast MOSFET gate charging and discharging.
The UC3843B provides cycle-by-cycle current limiting with a typical 1V current-sense threshold. It also includes a 2.5V error-amplifier reference and a nominal 5V reference output for oscillator timing and auxiliary control functions.
The UC3843BD1013TR is supplied in an 8-pin SO-8 surface-mount package using tape-and-reel packaging. ST classifies this orderable part as Industrial grade and ECOPACK 2 compliant, and currently lists it as an Active product in volume production.
Key Specifications
- Manufacturer: STMicroelectronics
- Manufacturer Part Number: UC3843BD1013TR
- Device Type: Current-Mode PWM Controller
- Control Method: Fixed-Frequency Peak Current Mode
- Number of Outputs: 1
- Maximum Operating Frequency: 500kHz
- Guaranteed Oscillator Frequency: 250kHz
- Typical Maximum Duty Cycle: 96%
- Available Duty-Cycle Range: Approximately 0% to 100%
- Typical UVLO Start Threshold: 8.4V
- UVLO Start-Threshold Range: 7.8V to 9.0V
- Typical UVLO Turn-Off Threshold: 7.6V
- UVLO Turn-Off Range: 7.0V to 8.2V
- Maximum Supply Voltage: 30V
- Typical Startup Current: 0.3mA
- Maximum Startup Current: 0.5mA
- Typical Operating Supply Current: 12mA
- Maximum Operating Supply Current: 17mA
- Peak Output Current: ±1A
- Typical Output Rise Time: 50ns
- Typical Output Fall Time: 50ns
- Typical Current-Sense Threshold: 1V
- Error-Amplifier Reference: 2.5V
- Nominal Reference Output: 5V
- Current Limiting: Cycle-by-Cycle
- Protection: Undervoltage Lockout
- Automatic Feed-Forward Compensation: Supported
- Maximum SO-8 Power Dissipation: 800mW at TA≤25°C
- Absolute Maximum Junction Temperature Range: −40°C to +150°C
- Package: SO-8
- Number of Pins: 8
- Mounting Type: Surface Mount
- Product Grade: Industrial
- Packaging: Tape and Reel
- Environmental Grade: ECOPACK 2
- Product Status: Active / Volume Production
Pin Functions
- Pin 1 COMP: Error-amplifier output and loop compensation
- Pin 2 VFB: Inverting feedback input
- Pin 3 ISENSE: Current-sense input
- Pin 4 RT/CT: Oscillator-frequency and duty-cycle programming
- Pin 5 GND: Control and power ground
- Pin 6 OUTPUT: External power-MOSFET gate drive
- Pin 7 VCC: Controller supply input
- Pin 8 VREF: 5V reference output
Typical Applications
Suitable for flyback power supplies, boost converters, offline AC-DC supplies, isolated and non-isolated DC-DC converters, power adapters, chargers, and auxiliary power supplies. Startup networks, VCC bias power, oscillator frequency, current sensing, slope compensation, MOSFET gate charge, and feedback-loop stability should be verified in the final design.
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