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STMicroelectronics E-UC3845BD1
- Part No.:
- E-UC3845BD1
- Manufacturer:
- STMicroelectronics
- Category:
- DC DC Switching Controllers
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
E-UC3845BD1.pdf
- Description:
- IC REG CTRLR BOOST/FLYBACK 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,627
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Product details
Overview
E-UC3845BD1 from STMicroelectronics is a current-mode PWM controller IC designed for DC-DC and off-line power supplies, featuring 8.4 V turn-on/7.6 V turn-off UVLO thresholds, ≤50% maximum duty cycle (due to internal toggle flip-flop), and guaranteed 250 kHz oscillator frequency with ±3% variation over temperature and supply. It delivers 1 A peak totem-pole output to drive N-channel MOSFETs and integrates a trimmed 5.00 V ±10 mV reference with <0.5 mA start-up current - used in low-voltage AC-DC adapters and isolated flyback converters.
For engineers reviewing the E-UC3845BD1 datasheet, E-UC3845BD1 pinout, E-UC3845BD1 application, or E-UC3845BD1 equivalent, key selection criteria include its 7.6–8.4 V UVLO window, 0–50% duty cycle limitation, current-sense gain of 3.0 V/V, 150 ns max output rise/fall time, and SO8 package compatibility with legacy UC384xB designs requiring reduced conduction loss and tight input voltage range operation.
Technical Context
The E-UC3845BD1 implements fixed-frequency current-mode control using an internal oscillator with RT/CT programmability, a high-gain error amplifier (90 dB open-loop gain, 1 MHz bandwidth), and a latched PWM comparator that enables cycle-by-cycle current limiting. Its internal toggle flip-flop blanks the output every other clock cycle, enforcing a hard 50% maximum duty cycle - distinguishing it from UC3842B/3B.
UVLO hysteresis (0.8 V) ensures reliable start-up under brown-out conditions, while the 5 V reference provides stable biasing for CT charging and feedback divider networks. The current-sense path features 3.0 V/V gain and 150 ns propagation delay, optimized for fast overcurrent response in discontinuous conduction mode (DCM) flyback topologies.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Oscillator Frequency | 250 kHz guaranteed at Tj = 25°C; supports up to 500 kHz with external RT/CT tuning - sets switching period for DCM flyback timing control. |
| UVLO Threshold | 8.4 V (on) / 7.6 V (off); 0.8 V hysteresis prevents chatter during low-line operation - ideal for 9–12 V input AC-DC adapters. |
| Max Duty Cycle | 48% typical (47–50% range); enforced by internal toggle flip-flop - limits transformer reset time and prevents core saturation in flyback designs. |
| Reference Voltage | 5.00 V ±10 mV at 1 mA load; <0.2 mV/°C drift - enables precise feedback loop scaling without external trimming. |
| Output Drive | ±1 A peak sink/source; 0.4 V low-level saturation at 20 mA - directly drives gate of 1 Ω gate charge MOSFETs without buffer stage. |
| Current Sense Gain | 3.0 V/V (2.85–3.15 V/V); 1 V threshold at COMP input - converts 0.33 V sense resistor drop into full-scale PWM shutdown signal. |
| Start-up Current | ≤0.5 mA at Vi = 6.5 V - allows use of high-value startup resistor (>1 MΩ) to minimize no-load power loss. |
Pinout & Package
Package: SO8 (Small Outline Integrated Circuit, 150 °C/W junction-to-ambient thermal resistance). Pin functions validated per STMicroelectronics UC384xB datasheet (D95IN332).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (COMP) | Error amplifier output | Provides high-impedance node for Type II/III compensation network - connects to feedback divider and optocoupler cathode in isolated designs. |
| 2 (VFB) | Inverting input of error amplifier | Receives scaled output voltage via resistor divider; 2.50 V nominal setpoint defines regulation target for secondary-side feedback. |
| 3 (ISENSE) | Current sense comparator input | Accepts voltage from primary-side current-sense resistor; 1 V trip point triggers PWM latch reset - enables cycle-by-cycle current limiting. |
| 4 (RT/CT) | Oscillator timing interface | Connects RT to VREF (pin 8) and CT to GND (pin 5); sets fOSC and influences max duty cycle via discharge current (7.8–8.8 mA). |
| 5 (GROUND) | Signal and power ground reference | Single-point return for control logic, oscillator, and error amp - must be star-connected to minimize noise coupling into ISENSE path. |
| 6 (OUTPUT) | Totem-pole gate driver output | Sources/sinks up to 1 A; low-state impedance <0.4 V @ 20 mA - directly switches MOSFET gate with <150 ns edge times into 1 nF load. |
| 7 (Vi / VCC) | Positive supply input | Operates from 7.6–30 V; internal zener clamps at 36 V - powered from auxiliary winding or linear regulator in self-biased flyback. |
| 8 (VREF) | 5 V precision reference output | Supplies 1 mA typical to RT; stable ±10 mV over line/load/temp - powers timing network and provides feedback reference for VFB divider. |
Key Features
| Feature | Design Value |
|---|---|
| Latched PWM with cycle-by-cycle current limiting | Prevents MOSFET overcurrent during overload or short-circuit by forcing single-cycle shutdown until next clock edge - eliminates need for external fault latching. |
| Internally trimmed 5.00 V reference | Eliminates external voltage reference IC and reduces BOM count; maintains ±10 mV accuracy across 0–70°C ambient - improves output regulation stability. |
| Low start-up current (<0.5 mA) | Enables high-value startup resistor (e.g., 2.2 MΩ) to reduce standby power to <100 mW in no-load condition - meets Energy Star Level VI requirements. |
| Toggle flip-flop duty cycle clamp | Hard-limits max on-time to 50%, preventing transformer saturation in flyback converters operating below minimum load - avoids need for external duty cycle limiter. |
| High-current totem-pole output | Drives 1 nF gate capacitance with <150 ns rise/fall time - supports MOSFETs with Qg ≤ 20 nC without external driver, reducing layout complexity and cost. |
Applications
| AC-DC Adapter | Flyback SMPS |
|---|---|
|
Use Scenario: 12 V/1 A isolated wall adapter for IoT sensors with universal 90–264 VAC input. IC Role / Device Role / Timing Role: Primary-side PWM controller implementing DCM flyback topology; regulates output via optocoupler feedback to VFB pin; sets 250 kHz switching frequency via RT = 10 kΩ, CT = 3.3 nF. Use Value: 8.4 V UVLO ensures reliable start-up even with degraded bulk capacitor; 50% duty cycle limit prevents transformer saturation during light-load burst-mode operation. |
Use Scenario: 5 V/2 A offline power supply for industrial PLC I/O modules requiring reinforced isolation and low EMI. IC Role / Device Role / Timing Role: Current-mode controller managing primary-side switching; senses peak current via 0.22 Ω shunt; uses COMP pin for slope compensation network to stabilize DCM operation. Use Value: 3.0 V/V current-sense gain enables accurate 1 A current limit with <5% tolerance; 150 ns propagation delay ensures fast overcurrent response (<500 ns total fault clearance). |
| USB-C PD Auxiliary Supply | Medical Isolated DC-DC Module |
|
Use Scenario: 9 V/0.5 A auxiliary rail in USB-C PD sink design, powered from main buck converter's auxiliary winding. IC Role / Device Role / Timing Role: Secondary-side regulated flyback controller; VREF pin supplies timing network and feedback reference; OUTPUT pin drives 600 V Si MOSFET. Use Value: 7.6 V UVLO matches auxiliary winding voltage profile; <0.5 mA start-up current minimizes no-load consumption - critical for always-on USB-C port detection. |
Use Scenario: 3.3 V/0.3 A isolated DC-DC module for patient-monitoring front-end analog circuitry requiring 4 kV reinforced isolation. IC Role / Device Role / Timing Role: Primary-side controller in transformer-isolated flyback; uses internal 5 V reference to bias optocoupler LED; GROUND pin referenced to primary-side earth. Use Value: Trimmed oscillator guarantees 250 kHz ±3% across -40 to +105°C - ensures consistent EMI signature for EMC certification; low operating current (12–17 mA) reduces thermal stress in sealed enclosure. |
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 |
|---|---|---|---|
| UC3845N | PDIP-8 package; 100 °C/W RθJA; identical electrical specs except higher thermal resistance and through-hole mounting. | Preferred for prototyping or low-volume through-hole PCBs; unsuitable for high-density SMT layouts or >0.8 W dissipation. | Select when manual assembly or legacy board rework is required; avoid in thermally constrained SMT designs exceeding 0.5 W ambient power. |
| TL494CN | Fixed 200 kHz oscillator; dual-output push-pull; no integrated UVLO hysteresis; requires external 5 V reference and duty cycle clamp. | Used in half-bridge or push-pull topologies; lacks cycle-by-cycle current limiting and auto-restart capability of UC3845. | Choose only for non-isolated forward or push-pull converters where dual outputs and adjustable dead time are needed - not a drop-in replacement. |
Compared with UC3845N, E-UC3845BD1 offers superior thermal performance (150 vs. 100 °C/W) and SMT manufacturability; versus TL494CN, it provides integrated UVLO, current-mode control, and single-MOSFET drive - reducing component count by ≥4 parts in flyback designs.
Availability
E-UC3845BD1 is available at Aetrix Electronics and suitable for AC-DC adapters, isolated flyback SMPS, and medical DC-DC modules requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.
Supply support for E-UC3845BD1 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
STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, delivering silicon solutions for automotive, industrial, and power management applications since 1987.
E-UC3845BD1 belongs to the UC384xB family of current-mode PWM controllers, designed specifically for cost-sensitive, high-efficiency off-line and DC-DC power conversion systems requiring minimal external components and robust protection features.
FAQ
What is the maximum recommended operating temperature for E-UC3845BD1?
The E-UC3845BD1 has a specified junction operating temperature range of –40°C to +150°C. For continuous operation in SO8 package, thermal design must ensure junction temperature stays within this limit - typically requiring ≤0.5 W power dissipation at 70°C ambient without heatsink, based on 150 °C/W RθJA. Derating curves in the datasheet confirm 100% rated performance up to +105°C case temperature.
Can E-UC3845BD1 replace UC3842BD1 in an existing design?
No - E-UC3845BD1 is not a direct replacement for UC3842BD1 due to fundamental functional differences: UC3845BD1 enforces ≤50% maximum duty cycle via internal toggle flip-flop, while UC3842BD1 supports up to 100%. Additionally, UVLO thresholds differ (8.4 V/7.6 V vs. 16 V/10 V), making E-UC3845BD1 unsuitable for standard off-line applications without circuit redesign.
Does E-UC3845BD1 support external synchronization?
Yes - E-UC3845BD1 supports external clock synchronization via the RT/CT pin. As shown in Figure 22 of the datasheet, an external sync signal can override the internal oscillator by injecting a square wave through a diode clamp network, enabling multi-controller phase interleaving or EMI spreading. The internal oscillator is disabled when external sync amplitude exceeds 300 mV peak.
What is the purpose of the toggle flip-flop in E-UC3845BD1?
The toggle flip-flop in E-UC3845BD1 blanks the OUTPUT pin every other clock cycle, enforcing a hard 50% maximum duty cycle. This prevents transformer core saturation in flyback converters operating at low line voltages or light loads, eliminating the need for external duty cycle limiting circuits and improving reliability in DCM operation without sacrificing control loop stability.
E-UC3845BD1 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Output Type:
- Transistor Driver
- Function:
- Step-Up/Step-Down
- Output Configuration:
- Positive, Isolation Capable
- Topology:
- Boost, Flyback
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 7.6V ~ 30V
- Frequency - Switching:
- Up to 500kHz
- Duty Cycle (Max):
- 48%
- Synchronous Rectifier:
- No
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Frequency Control
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
E-UC3845BD1 FAQ
1.How can I place an order for E-UC3845BD1 through Aetrix?
Please submit a Request for Quotation (RFQ) for E-UC3845BD1 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 E-UC3845BD1 reliable?
The price and inventory of E-UC3845BD1 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for E-UC3845BD1 is usually 5 days.
3.What payment methods are accepted for E-UC3845BD1?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for E-UC3845BD1 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for E-UC3845BD1?
E-UC3845BD1 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your E-UC3845BD1 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 E-UC3845BD1?
For technical support, including E-UC3845BD1 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your E-UC3845BD1 requirements.
6.How does Aetrix verify that E-UC3845BD1 is sourced from the original manufacturer or authorized distributors?
All E-UC3845BD1 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 E-UC3845BD1 meets industry standards.
7.What is the process for return or replacement of E-UC3845BD1?
All E-UC3845BD1 units undergo pre-shipment inspection (PSI). If there is an issue with E-UC3845BD1, 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 E-UC3845BD1 part is unused and in its original packaging.
Return procedure for E-UC3845BD1:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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