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STMicroelectronics UC2845BD1
- Part No.:
- UC2845BD1
- Manufacturer:
- STMicroelectronics
- Category:
- DC DC Switching Controllers
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
UC2845BD1.pdf
- Description:
- IC REG CTRLR BOOST/FLYBACK 8SO
- Quantity:
- Payment:
- Shipping:
Inventory:1,867
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Product details
Overview
UC2845BD1 from STMicroelectronics is a high-performance current-mode PWM controller IC designed for fixed-frequency DC-DC and off-line power supplies. It features an internally trimmed oscillator (250 kHz guaranteed), 47–50% maximum duty cycle, UVLO thresholds of 8.4 V (on) / 7.6 V (off), and a totem-pole output capable of ±1 A peak drive current-optimized for driving N-channel MOSFETs in flyback and forward converters.
For engineers reviewing the UC2845BD1 datasheet, UC2845BD1 pinout, UC2845BD1 application, or UC2845BD1 equivalent, this device is selected for precision current-mode control where low start-up current (<0.5 mA), tight reference voltage (5.00 V ±5 mV), latch-based cycle-by-cycle current limiting, and internal slope compensation support stable operation in isolated topologies with wide input ranges.
Technical Context
The UC2845BD1 implements current-mode control using a dedicated current-sense comparator with 3.0 V/V gain and 1 V trip threshold, synchronized to a resistor-capacitor programmable oscillator (RT/CT). Its internal toggle flip-flop enforces ≤50% duty cycle by blanking every other clock cycle-preventing subharmonic oscillation in continuous-conduction-mode flyback designs.
It integrates a 2.5 V error amplifier reference, 5 V ±5 mV bandgap reference with <0.2 mV/°C drift, under-voltage lockout with hysteresis, and a high-current totem-pole output stage (13.5 V VOH at 20 mA, 0.4 V VOL at 20 mA) directly compatible with standard gate-drive requirements of power MOSFETs.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Oscillator Frequency | 250 kHz guaranteed at 25°C; supports up to 500 kHz via RT/CT tuning-enables compact magnetics and EMI optimization. |
| Max Duty Cycle | 47–50% (typical); enforced by internal toggle flip-flop-eliminates need for external slope compensation in CCM flyback. |
| UVLO Thresholds | 8.4 V turn-on / 7.6 V turn-off; optimized for low-input-voltage DC-DC applications like telecom or battery-fed systems. |
| Reference Voltage | 5.00 V ±5 mV at 1 mA load; trimmed for accuracy at error amp input-reduces feedback divider tolerance burden. |
| Output Drive | ±1 A peak sink/source; 13.5 V high-level / 0.4 V low-level at 20 mA-directly drives gate capacitance of medium-power MOSFETs. |
| Start-up Current | <0.5 mA at 6.5 V supply-enables high-impedance bias networks and reduces auxiliary winding losses. |
| Error Amp GBW | 0.7–1 MHz unity-gain bandwidth-supports stable loop compensation for fast transient response in regulated outputs. |
Pinout & Package
UC2845BD1 is housed in an SO8 (Small Outline 8-pin) package per JEDEC MS-012, with 1.27 mm lead pitch and surface-mount compatibility. Thermal resistance is 150 °C/W (junction-to-ambient).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - COMP | Error Amplifier Output | Open-collector node for loop compensation network-connects external RC/Zener to set phase margin and crossover frequency. |
| 2 - VFB | Error Amp Inverting Input | Receives feedback voltage from output divider-sets regulation point when referenced to internal 2.5 V virtual ground. |
| 3 - ISENSE | Current Sense Input | Accepts voltage from sense resistor; comparator trips at ~1 V-enables precise cycle-by-cycle peak current limiting. |
| 4 - RT/CT | Oscillator Timing Node | Connects RT to VREF and CT to GND-programs frequency and max duty cycle; discharge current 7.5–8.8 mA at 25°C. |
| 5 - GROUND | Signal & Power Return | Common reference for all analog circuits and power switch return-requires star grounding near pin 5 for noise immunity. |
| 6 - OUTPUT | Gate Drive Output | Totem-pole stage sourcing/sinking up to 1 A-drives MOSFET gate directly; low-state ensures safe FET turn-off during fault. |
| 7 - VCC | Supply Input | Operates from 7.6–30 V; self-limiting above 30 V-accepts auxiliary winding or bias supply with minimal external filtering. |
| 8 - VREF | 5 V Reference Output | Supplies charging current to CT via RT-stable 5 V source for timing and external circuitry; short-circuit protected. |
Key Features
| Feature | Design Value |
|---|---|
| Latched PWM with cycle-by-cycle current limit | Prevents multiple switching events per cycle during overcurrent-ensures predictable fault shutdown and thermal safety. |
| Internally trimmed 5 V reference | ±5 mV accuracy at 25°C and ±25 mV over full temperature range-reduces need for precision external references in cost-sensitive designs. |
| Low start-up current (<0.5 mA) | Enables use of high-value startup resistors-minimizes power loss in offline adapters with wide AC input ranges. |
| Automatic feed-forward compensation | Input voltage variation directly modulates oscillator ramp-improves line transient rejection without additional circuitry. |
| Toggle flip-flop duty cycle clamp | Hard-limits max on-time to ~50%-avoids subharmonic instability in CCM flyback without external slope injection. |
Applications
| AC-DC Adapter | Flyback SMPS |
|---|---|
|
Use Scenario: 5–24 V output, 10–65 W universal-input offline adapter for consumer electronics. IC Role / Device Role / Timing Role: Primary-side PWM controller implementing current-mode regulation with fixed 250 kHz switching and automatic feed-forward. Use Value: Enables compact transformer design, tight output regulation across line/load, and inherent overload protection via latched current limit. |
Use Scenario: Isolated 12 V/2 A flyback converter in industrial IoT gateway power supply. IC Role / Device Role / Timing Role: Current-sense-based primary-side controller with ≤50% duty cycle enforcement to maintain stability in CCM operation. Use Value: Eliminates need for optocoupler feedback compensation and external slope generator-reducing BOM count and layout complexity. |
| Telecom DC-DC Module | Battery Charger Front-End |
|
Use Scenario: 48 V input to 5 V/3 A intermediate bus converter in telecom shelf power system. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller with low UVLO (7.6 V) enabling operation down to brownout conditions. Use Value: Maintains regulation during input dips; low start-up current extends hold-up time using small bulk capacitors. |
Use Scenario: 12–36 V input Li-ion battery charger front-end with constant-current/constant-voltage control. IC Role / Device Role / Timing Role: Primary-side controller regulating output via secondary-side feedback signal conditioned through optocoupler. Use Value: High-accuracy 5 V reference and tight error amp offset enable ±1% output voltage tolerance critical for battery safety. |
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 |
|---|---|---|---|
| UC3845BN | Same core architecture but rated for 0–70°C ambient (vs. UC2845BD1's –40–105°C industrial grade) | Targeted for commercial equipment; lacks extended temperature qualification and tighter parameter binning | Select when operating environment stays within 0–70°C and cost sensitivity outweighs industrial reliability needs |
| TL494CN | Voltage-mode (not current-mode); dual-output; adjustable dead time; no integrated current sense comparator or UVLO hysteresis | Suited for push-pull or half-bridge topologies requiring complementary outputs-not drop-in for flyback current-mode designs | Choose only when topology requires dual outputs or voltage-mode control; requires redesign of sensing, compensation, and protection |
Compared with UC3845BN, UC2845BD1 offers wider temperature range and tighter electrical specs; versus TL494CN, it delivers simpler, more robust current-mode implementation for single-switch isolated converters-but lacks dual-output flexibility.
Availability
UC2845BD1 is available at Aetrix Electronics and suitable for AC-DC adapters, flyback SMPS, telecom DC-DC modules, and battery charger front-ends requiring stable component supply, long-term lifecycle continuity, and industrial-grade temperature performance.
Supply support for UC2845BD1 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, power, and embedded applications since 1987.
The UCx84xB family was engineered specifically for cost-effective, high-reliability current-mode PWM control in isolated and non-isolated DC-DC converters-emphasizing minimal external components, robust fault handling, and production-ready parameter stability.
FAQ
What is the key functional difference between UC2845BD1 and UC2842BD1?
The UC2845BD1 features under-voltage lockout thresholds of 8.4 V (turn-on) and 7.6 V (turn-off), and a maximum duty cycle limited to 47–50% by an internal toggle flip-flop. In contrast, UC2842BD1 has higher UVLO thresholds (16 V/10 V) and supports up to 100% duty cycle-making UC2845BD1 better suited for low-input-voltage DC-DC applications where subharmonic instability must be avoided in continuous conduction mode.
Can UC2845BD1 drive a SiC MOSFET directly?
No-UC2845BD1's output stage is rated for ±1 A peak current and 13.5 V VOH, which meets gate-drive requirements for standard silicon MOSFETs but lacks the negative turn-off voltage, high dV/dt immunity, and fast rise/fall times needed for reliable SiC MOSFET switching. A dedicated gate driver IC (e.g., STGAP2SIC) is required between UC2845BD1 and SiC devices.
Is external slope compensation required when using UC2845BD1 in flyback CCM?
No-UC2845BD1 includes an internal toggle flip-flop that inherently limits maximum duty cycle to ≤50%, eliminating subharmonic oscillation in continuous conduction mode flyback converters without requiring external ramp injection. This is a defining feature distinguishing UC2844B/UC2845B from UC2842B/UC2843B variants.
What is the recommended minimum CT value for stable 250 kHz operation?
For guaranteed 250 kHz oscillator frequency at 25°C, STMicroelectronics specifies RT = 6.2 kΩ and CT = 1 nF in the datasheet. With UC2845BD1's typical discharge current of 7.5–8.8 mA, CT must be ≥1 nF to ensure sufficient timing capacitor charge/discharge margin-smaller values risk frequency drift or startup failure due to leakage and parasitic effects.
UC2845BD1 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Up, 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:
- -40°C ~ 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
UC2845BD1 FAQ
1.How can I place an order for UC2845BD1 through Aetrix?
Please submit a Request for Quotation (RFQ) for UC2845BD1 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 UC2845BD1 reliable?
The price and inventory of UC2845BD1 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC2845BD1 is usually 5 days.
3.What payment methods are accepted for UC2845BD1?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC2845BD1 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for UC2845BD1?
UC2845BD1 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your UC2845BD1 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 UC2845BD1?
For technical support, including UC2845BD1 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC2845BD1 requirements.
6.How does Aetrix verify that UC2845BD1 is sourced from the original manufacturer or authorized distributors?
All UC2845BD1 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 UC2845BD1 meets industry standards.
7.What is the process for return or replacement of UC2845BD1?
All UC2845BD1 units undergo pre-shipment inspection (PSI). If there is an issue with UC2845BD1, 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 UC2845BD1 part is unused and in its original packaging.
Return procedure for UC2845BD1:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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