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Texas Instruments UC3845ADTRG4
- Part No.:
- UC3845ADTRG4
- Manufacturer:
- Texas Instruments
- Category:
- Power Supply Controllers, Monitors
- Package:
- 14-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
UC3845ADTRG4.pdf
- Description:
- IC REG CTRLR MULT TOP 14SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,882
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Product details
Overview
UC3845ADTRG4 from Texas Instruments is a current-mode PWM controller IC designed for off-line and DC-DC switch-mode power supplies. It features 8.3 mA trimmed oscillator discharge current, <0.5 mA start-up current, undervoltage lockout with 8.4 V turn-on/7.6 V turn-off hysteresis, 500 kHz max switching frequency, and a 1 A totem-pole output stage driving MOSFET gates directly in flyback and forward converters.
For engineers reviewing the UC3845ADTRG4 datasheet, UC3845ADTRG4 pinout, UC3845ADTRG4 application, or UC3845ADTRG4 equivalent, key selection criteria include its 50% maximum duty cycle limit, internal 5 V ±1% reference, pulse-by-pulse current limiting, automatic feedforward compensation, and SOIC-8 package compatibility with board-level thermal management requirements.
Technical Context
The UC3845ADTRG4 implements peak-current mode control using an internal error amplifier (80 dB open-loop gain, 1 MHz unity-gain bandwidth) and a dedicated current-sense comparator clamping input at 1 V. Its oscillator uses external RT/CT components with trimmed 8.3 mA discharge current to ensure stable 50% max duty cycle across temperature and process variation.
During undervoltage lockout (UVLO), the device draws only 0.3–0.5 mA and forces OUTPUT low while sinking ≥10 mA at ≤1.2 V - preventing parasitic MOSFET turn-on during startup. The 1 A totem-pole output drives gate capacitance directly without external buffers, supporting fast rise/fall times (<150 ns with 1 nF load).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Max switching frequency | 500 kHz - enables compact magnetics and high-power-density SMPS designs |
| Max duty cycle | 50% - limits conduction time for safe operation in flyback topologies with transformer reset |
| Oscillator discharge current | 8.3 mA (typ) - trimmed for precise timing and consistent 50% duty cycle programming |
| Start-up current | <0.5 mA - reduces power loss in high-voltage start-up resistors for off-line AC/DC supplies |
| VREF accuracy | 4.9 V to 5.1 V (0°C to 70°C) - provides stable feedback reference for ±1% output voltage regulation |
| UVLO threshold | 8.4 V turn-on / 7.6 V turn-off - narrow hysteresis optimized for regulated DC-DC input applications |
| Output drive capability | ±1 A - directly drives power MOSFET gates without external buffer stages |
Pinout & Package
UC3845ADTRG4 is housed in an 8-pin SOIC (D) package measuring 4.90 mm × 6.00 mm, with standard JEDEC MS-012AC footprint and 1.27 mm pitch.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - COMP | Error amplifier output | Low-impedance node (80 dB gain, 1 MHz GBW) feeding PWM comparator; sinks up to 6 mA |
| 2 - FB | Error amplifier inverting input | Receives opto-coupler or resistor-divider feedback; sets output voltage regulation point |
| 3 - ISENSE | Current sense input | Accepts voltage from primary-side sense resistor; clamped at 1 V for cycle-by-cycle overcurrent protection |
| 4 - RT/CT | Oscillator timing input | Connects external resistor (5–100 kΩ) and capacitor (470 pF–4.7 nF) to set switching frequency |
| 5 - GND | Signal ground reference | Return path for error amplifier, comparators, and logic; must be star-connected to minimize noise coupling |
| 6 - OUTPUT | Gate driver output | Totem-pole stage sourcing/sinking ±1 A; drives MOSFET gate directly with <150 ns rise/fall (1 nF load) |
| 7 - VCC | Bias supply input | Accepts 11–30 V; powers internal circuitry and gate driver; UVLO active below 7.6 V |
| 8 - VREF | 5 V reference output | Stable 5 V ±1% source for feedback divider and external circuitry; short-circuit protected at ~100 mA |
Key Features
| Feature | Design Value |
|---|---|
| Pulse-by-pulse current limiting | Hardware-based overcurrent protection per switching cycle using 1 V clamped ISENSE input |
| Automatic feedforward compensation | Internal circuitry rejects input voltage ripple effects on duty cycle, improving line transient response |
| Enhanced load response characteristics | Optimized error amplifier bandwidth and gain allow fast correction of output voltage deviations under dynamic load steps |
| Double pulse suppression | Prevents multiple output pulses during transient conditions, ensuring clean single-pulse-per-cycle operation |
| Internally-trimmed bandgap reference | 5 V reference with ±1% tolerance over 0°C–70°C eliminates need for external calibration or trimming |
Applications
| Industrial DC-DC Converter | AC-DC Adapter |
|---|---|
Use Scenario: Regulated 12 V/5 A output from 24 V industrial bus with wide input tolerance and EMI constraints. IC Role / Device Role / Timing Role: Primary-side current-mode PWM controller setting switching frequency, duty cycle, and peak current limit. Use Value: 50% max duty cycle prevents transformer saturation; 8.4 V/7.6 V UVLO ensures reliable startup under brownout conditions. | Use Scenario: Universal-input (85–265 VAC) 12 V/48 W flyback adapter for consumer electronics. IC Role / Device Role / Timing Role: Off-line current-mode controller managing primary-side regulation via opto-isolated feedback loop. Use Value: <0.5 mA start-up current minimizes dissipation in high-voltage start-up resistor; 1 A gate drive supports fast MOSFET switching. |
| Battery Charger PSU | LED Driver Module |
Use Scenario: Constant-voltage/constant-current battery charger for 12 V sealed lead-acid packs in backup systems. IC Role / Device Role / Timing Role: Current-mode controller implementing CC/CV transition using ISENSE and FB inputs. Use Value: Pulse-by-pulse limiting protects against short-circuit events during battery fault conditions; 500 kHz operation allows small filter components. | Use Scenario: Isolated constant-current LED driver powering 36 V string from 120 VAC input. IC Role / Device Role / Timing Role: Primary-side PWM controller regulating LED current via secondary-side feedback through optocoupler. Use Value: Automatic feedforward compensation maintains stable LED current despite AC line fluctuations; 5 V VREF powers optocoupler bias network. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar current-mode PWM controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UC3845BDTRG4 | Higher VREF accuracy (4.95–5.05 V vs. 4.9–5.1 V); tighter oscillator initial accuracy (±5% vs. ±10%) | Better suited for precision-output applications requiring tighter regulation stability over temperature | Select UC3845BDTRG4 when output voltage tolerance ≤±0.5% is required and cost premium is acceptable |
| UCC38C45DR | Improved ESD rating (±4 kV HBM vs. ±2 kV); wider operating temperature (–40°C to 105°C vs. 0°C to 70°C) | Preferred for automotive or extended-temperature industrial environments where reliability under stress is critical | Choose UCC38C45DR for designs requiring enhanced robustness in harsh thermal or ESD-prone settings |
Compared with UC3845BDTRG4 and UCC38C45DR, UC3845ADTRG4 offers the lowest-cost entry into current-mode control with validated 50% duty cycle behavior and proven SOIC-8 manufacturability - ideal for cost-sensitive, commercial-grade AC-DC and DC-DC power supplies operating at 0°C–70°C.
Availability
UC3845ADTRG4 is available at Aetrix Electronics and suitable for industrial DC-DC converters, universal-input AC-DC adapters, and battery-operated power supplies requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.
Supply support for UC3845ADTRG4 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Texas Instruments is a global semiconductor company delivering analog and embedded processing solutions with leadership in power management, signal chain, and microcontrollers.
The UCx84xA product line was engineered specifically for cost-effective, high-reliability current-mode switch-mode power supply control - targeting off-line AC-DC, isolated DC-DC, and industrial power module applications.
FAQ
What is the maximum duty cycle supported by UC3845ADTRG4?
The UC3845ADTRG4 supports a maximum duty cycle of 50%, as confirmed in the Device Comparison Table and Electrical Characteristics section of the datasheet. This fixed limit is inherent to the UC3845A variant and ensures safe operation in flyback topologies where transformer reset must occur within each switching cycle. Unlike UC3842A/UC3843A variants, UC3845ADTRG4 does not support 100% duty cycle operation.
Does UC3845ADTRG4 require an external current-sense resistor?
Yes, UC3845ADTRG4 requires an external current-sense resistor connected to the ISENSE pin (Pin 3). The device monitors the voltage drop across this resistor to implement pulse-by-pulse current limiting, with internal clamping at 1 V. Typical values range from 0.1 Ω to 1 Ω depending on peak primary current, and a small RC filter is recommended to suppress switching noise.
What is the purpose of the RT/CT pin on UC3845ADTRG4?
The RT/CT pin (Pin 4) on UC3845ADTRG4 sets the oscillator frequency via external resistor (RT) and capacitor (CT) components. With RT = 10 kΩ and CT = 3.3 nF, typical operation reaches 500 kHz. TI recommends RT between 5 kΩ and 100 kΩ and CT between 470 pF and 4.7 nF to maintain stability and achieve the specified frequency range.
How does UC3845ADTRG4 handle undervoltage lockout (UVLO)?
UC3845ADTRG4 implements UVLO with a turn-on threshold of 8.4 V and turn-off threshold of 7.6 V, providing 0.8 V hysteresis. During UVLO, the OUTPUT pin is forced low, the VREF output is disabled, and supply current drops to ≤0.5 mA. The device can sink ≥10 mA at ≤1.2 V on the OUTPUT pin during UVLO to prevent parasitic MOSFET turn-on.
Can UC3845ADTRG4 drive MOSFET gates directly without external drivers?
Yes, UC3845ADTRG4 integrates a high-current totem-pole output stage capable of sourcing and sinking up to 1 A, enabling direct drive of power MOSFET gates. Rise and fall times are ≤150 ns with a 1 nF capacitive load. A series gate resistor (e.g., 10–22 Ω) is still recommended to dampen ringing and limit peak current during switching transitions.
UC3845ADTRG4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- UCx84xA
- Package/Case:
- 14-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Discontinued at Digi-Key
- Programmable:
- -
- Applications:
- PWM Controller
- Voltage - Input:
- -0.3V ~ 6.3V
- Voltage - Supply:
- 7.6V ~ 30V
- Current - Supply:
- 11 mA
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 14-SOIC
UC3845ADTRG4 FAQ
1.How can I place an order for UC3845ADTRG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for UC3845ADTRG4 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for UC3845ADTRG4 reliable?
The price and inventory of UC3845ADTRG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC3845ADTRG4 is usually 5 days.
3.What payment methods are accepted for UC3845ADTRG4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC3845ADTRG4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for UC3845ADTRG4?
UC3845ADTRG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your UC3845ADTRG4 order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for UC3845ADTRG4?
For technical support, including UC3845ADTRG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC3845ADTRG4 requirements.
6.How does Aetrix verify that UC3845ADTRG4 is sourced from the original manufacturer or authorized distributors?
All UC3845ADTRG4 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that UC3845ADTRG4 meets industry standards.
7.What is the process for return or replacement of UC3845ADTRG4?
All UC3845ADTRG4 units undergo pre-shipment inspection (PSI). If there is an issue with UC3845ADTRG4, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The UC3845ADTRG4 part is unused and in its original packaging.
Return procedure for UC3845ADTRG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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