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STMicroelectronics UC2845BN
- Part No.:
- UC2845BN
- Manufacturer:
- STMicroelectronics
- Category:
- DC DC Switching Controllers
- Package:
- 8-DIP (0.300", 7.62mm)
- Datasheet:
-
UC2845BN.pdf
- Description:
- IC REG CTRLR BST/FLYBK 8-MINIDIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,634
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Product details
Overview
UC2845BN from STMicroelectronics is a high-performance current-mode PWM controller IC designed for DC-DC and off-line fixed-frequency switching power supplies. It features 8.4 V turn-on / 7.6 V turn-off UVLO, ≤50% maximum duty cycle (via internal toggle flip-flop), 250 kHz guaranteed oscillator frequency, ±1 A totem-pole output, and 5.00 V ±5 mV trimmed reference - enabling precise voltage regulation in isolated flyback converters.
For engineers reviewing the UC2845BN datasheet, UC2845BN pinout, UC2845BN application, or UC2845BN equivalent, key selection criteria include its low-startup-current (<0.5 mA), cycle-by-cycle current limiting, automatic feed-forward compensation, and compatibility with N-channel MOSFET gate driving in cost-sensitive AC-DC adapters and industrial SMPS.
Technical Context
The UC2845BN implements current-mode control using an internal error amplifier, PWM latch, and current-sense comparator referenced to a 1 V threshold. Its oscillator uses RT/CT programming with discharge current of 7.8–8.8 mA, supporting operation up to 500 kHz while maintaining stable frequency via internal trimming.
Unlike UC2842BN/UC2843BN, it incorporates a toggle flip-flop that blanks the output every other clock cycle - enforcing a hard 0–50% duty cycle limit ideal for forward and half-bridge topologies requiring inherent dead-time control and reduced EMI.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Oscillator Frequency | 250 kHz guaranteed at 25°C; enables fixed-frequency design with predictable EMI profile and simplified filter sizing. |
| UVLO Threshold | 8.4 V (on) / 7.6 V (off) with hysteresis; ensures reliable start-up from low-voltage rails and prevents brown-out oscillation in battery-backed or wide-input systems. |
| Max Duty Cycle | ≤50% enforced by internal toggle flip-flop; eliminates need for external duty-cycle clamp in forward converters and improves transformer reset margin. |
| Output Drive | ±1 A peak source/sink capability; directly drives medium-power N-MOSFET gates without external buffer, reducing BOM count and layout complexity. |
| Reference Voltage | 5.00 V ±5 mV at 1 mA load; provides stable feedback reference for precision secondary-side regulation in isolated topologies. |
| Current Sense Gain | 3.0 V/V ±5%; converts sensed resistor voltage to accurate 1 V trip point for fast, repeatable overcurrent protection. |
| Start-up Current | <0.5 mA at 6.5 V; minimizes auxiliary winding losses and enables ultra-low-power no-load operation in energy-efficient adapters. |
Pinout & Package
UC2845BN is housed in an 8-pin PDIP (Minidip) package with 0.3-inch body width and through-hole mounting. Pin 5 serves as the common ground for both analog and power sections, requiring single-point grounding for noise immunity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - COMP | Error amplifier output | Provides access to EA output for loop compensation networks; connects to RC network between pins 1 and 2 for stability tuning. |
| 2 - VFB | Inverting input of error amplifier | Receives feedback voltage from output divider; sets regulated output voltage via ratio to 2.5 V internal reference. |
| 3 - ISENSE | Current sense input | Accepts voltage from primary-side current-sense resistor; triggers PWM shutdown when ≥1.0 V (gain-adjusted). |
| 4 - RT/CT | Oscillator timing node | Connects external RT resistor to VREF and CT capacitor to GND; programs frequency and discharge slope for ramp compensation. |
| 5 - GROUND | Analog + power ground | Single-point return path for all internal circuits; must be routed separately from power ground to avoid noise coupling. |
| 6 - OUTPUT | PWM output driver | Drives MOSFET gate directly; low-state output sinks up to 200 mA at ≤2.2 V, minimizing conduction loss during switch-off. |
| 7 - VCC | Supply input | Accepts 7.6–30 V unregulated input; powers internal bias, reference, and logic; includes UVLO hysteresis for clean enable/disable. |
| 8 - VREF | 5 V reference output | Supplies 5.00 V ±5 mV at up to 20 mA; powers RT/CT network and optional external circuitry with low-noise, temperature-stable source. |
Key Features
| Feature | Design Value |
|---|---|
| Latching PWM with cycle-by-cycle current limit | Guarantees immediate shutdown on overcurrent event, preventing MOSFET failure during short-circuit or overload conditions. |
| Internally trimmed 5 V reference with <0.2 mV/°C drift | Enables stable feedback across –40°C to +150°C junction range without external calibration or trimming components. |
| Automatic feed-forward compensation | Compensates for line-voltage variations in real time, improving transient response and reducing output voltage deviation under input ripple. |
| High-current totem-pole output stage | Delivers ±1 A peak drive with <150 ns rise/fall times into 1 nF load, ensuring fast MOSFET switching and reduced switching losses. |
| Low-startup supply current (<0.5 mA) | Reduces auxiliary winding size and losses in flyback designs, supporting compliance with EU CoC Tier 2 and DOE Level VI efficiency standards. |
Applications
| AC-DC Adapter | Industrial DC-DC Converter |
|---|---|
|
Use Scenario: 12 V/2 A wall adapter for networking equipment with universal AC input (90–264 VAC). IC Role / Device Role / Timing Role: Primary-side PWM controller implementing current-mode flyback topology with optocoupler feedback and 50% max duty cycle for safe transformer reset. Use Value: Enables compact design with minimal external parts, meets IEC 62368-1 creepage requirements, and achieves >85% efficiency at full load. |
Use Scenario: 24 V input to 5 V/3 A isolated DC-DC module for PLC I/O modules operating in harsh factory environments. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller regulating output via secondary-side TL431 shunt reference and optocoupler; UVLO ensures robust start-up after brownouts. Use Value: Provides reliable overcurrent protection, thermal stability across –40°C to +85°C ambient, and consistent regulation despite wide input transients. |
| LED Driver (Constant Voltage) | Telecom Power Supply |
|
Use Scenario: 12 V constant-voltage LED driver for signage applications with dimming interface and surge immunity. IC Role / Device Role / Timing Role: Primary-side controller managing MOSFET gate drive and current sensing; 250 kHz switching balances EMI filtering and magnetics size. Use Value: Supports smooth 0–10 V analog dimming via VFB pin, maintains ±2% output regulation under 10–100% load, and withstands 2 kV line-to-ground surges. |
Use Scenario: -48 V telecom rectifier supplying 3.3 V/10 A to base station control boards with strict hold-up time and ripple specs. IC Role / Device Role / Timing Role: Forward converter controller using UC2845BN's 50% duty cycle limit to ensure transformer flux balance and prevent saturation. Use Value: Delivers tight output regulation (±1%), supports remote ON/OFF via VFB pin, and sustains operation during 10 ms AC dropouts per GR-1089-CORE. |
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 pinout and electrical specs, but rated for 0°C to +70°C ambient (vs. UC2845BN's –40°C to +150°C junction range). | Not qualified for extended temperature industrial or automotive use; suitable only for commercial-grade indoor equipment. | Select UC3845BN only if ambient temperature remains within 0–70°C and cost is prioritized over ruggedness. |
| TL494CN | Fixed-frequency voltage-mode controller with dual outputs, adjustable dead time, and built-in 5 V reference - no current-sense comparator or latch. | Requires external current sensing and protection logic; lacks cycle-by-cycle limiting and automatic feed-forward. | Choose TL494CN only when dual-output push-pull or full-bridge topology is needed and current-mode control is not required. |
Compared with UC3845BN, UC2845BN offers wider temperature qualification and higher reliability for industrial deployment; versus TL494CN, it delivers superior transient response, simpler current protection, and lower component count in single-switch topologies.
Availability
UC2845BN is available at Aetrix Electronics and suitable for AC-DC adapters, industrial DC-DC converters, LED drivers, and telecom power supplies requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for UC2845BN 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, specializing in power management, analog, microcontrollers, and automotive ICs.
The UCx84xB series was developed specifically for cost-effective, high-reliability current-mode switching power supplies - targeting applications where minimal external components, robust fault handling, and precise regulation are critical.
FAQ
What is the maximum recommended operating frequency for UC2845BN?
The UC2845BN oscillator is guaranteed at 250 kHz, but its current-mode architecture supports stable operation up to 500 kHz with appropriate RT/CT selection and PCB layout. At frequencies above 300 kHz, attention to gate-drive loop inductance, current-sense filtering, and ground separation becomes critical to maintain noise immunity and latch reliability.
Can UC2845BN drive a P-channel MOSFET directly?
No - UC2845BN's OUTPUT pin is designed as a totem-pole stage that sources current when high and sinks when low, making it optimal for N-channel MOSFETs with source grounded. Driving a P-channel device would require level-shifting circuitry or an external driver, adding complexity and defeating the IC's integrated simplicity advantage.
How does the 50% duty cycle limitation affect transformer design in flyback topologies?
The internal toggle flip-flop enforces ≤50% duty cycle, which mandates a turns-ratio adjustment to maintain output voltage regulation - typically requiring higher primary-to-secondary ratio. This increases reflected voltage stress on the primary switch but guarantees safe transformer reset and eliminates risk of core saturation during startup or overload.
Is external slope compensation required when using UC2845BN in continuous conduction mode?
Yes - for flyback or boost converters operating in CCM with duty cycles >50%, external ramp injection (e.g., via CT pin) is necessary to prevent subharmonic oscillation. The UC2845BN does not integrate slope compensation; Figure 18 in the datasheet shows standard RC-based implementation using the VREF and RT/CT nodes.
UC2845BN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 8-DIP (0.300", 7.62mm)
- 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:
- Through Hole
- Supplier Device Package:
- 8-Mini DIP
UC2845BN FAQ
1.How can I place an order for UC2845BN through Aetrix?
Please submit a Request for Quotation (RFQ) for UC2845BN 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 UC2845BN reliable?
The price and inventory of UC2845BN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC2845BN is usually 5 days.
3.What payment methods are accepted for UC2845BN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC2845BN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for UC2845BN?
UC2845BN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your UC2845BN 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 UC2845BN?
For technical support, including UC2845BN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC2845BN requirements.
6.How does Aetrix verify that UC2845BN is sourced from the original manufacturer or authorized distributors?
All UC2845BN 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 UC2845BN meets industry standards.
7.What is the process for return or replacement of UC2845BN?
All UC2845BN units undergo pre-shipment inspection (PSI). If there is an issue with UC2845BN, 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 UC2845BN part is unused and in its original packaging.
Return procedure for UC2845BN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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