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HomeProductsIntegrated Circuits (ICs)PMIC - Voltage Regulators - DC DC Switching ControllersCS51221EDTB16G
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CS51221EDTB16G - onsemi

Manufacturer Part Number
CS51221EDTB16G
Manufacturer
onsemi
Allelco Part Number
98D-CS51221EDTB16G
Warranty
1 Year Allelco Warranty - Find out more
Stock Status:
12,131 pcs available, New & Original
Parts Description
IC REG CTRLR FWRD CONV 16TSSOP
Package
16-TSSOP
Data sheet
CS51221EDTB16G.pdf

PCN Obsolescence/ EOL

Cylindrical Battery Holders.pdf

Environmental Information

onsemi REACH.pdf onsemi RoHS.pdf
RoHs Status
 
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Specifications

CS51221EDTB16G Tech Specifications
onsemi - CS51221EDTB16G technical specifications, attributes, parameters and parts with similar specifications to onsemi - CS51221EDTB16G

Product Attribute Attribute Value
Manufacturer onsemi
Voltage - Supply (Vcc/Vdd) 3.8V ~ 15V
Topology Forward Converter
Synchronous Rectifier No
Supplier Device Package 16-TSSOP
Series -
Serial Interfaces -
Package / Case 16-TSSOP (0.173', 4.40mm Width)
Package Tube
Output Type Transistor Driver
Output Phases 1
Product Attribute Attribute Value
Output Configuration Positive, Isolation Capable
Operating Temperature -40°C ~ 85°C (TA)
Number of Outputs 1
Mounting Type Surface Mount
Function Step-Up/Step-Down
Frequency - Switching 1MHz
Duty Cycle (Max) 85%
Control Features Current Limit, Frequency Control, Ramp, Soft Start
Clock Sync Yes
Base Product Number CS51221

Environmental & Export Classifications

ATTRIBUTE DESCRIPTION
Moisture Sensitivity Level (MSL) 1 (Unlimited)
REACH Status REACH Unaffected
ECCN EAR99
HTSUS 8542.31.0001

Frequently Asked Questions(FAQ)

How does the CS51221EDTB16G handle voltage regulation in a forward converter topology when input supply varies between 3.8V and 15V?
The CS51221EDTB16G maintains stable output regulation across its specified supply range by dynamically adjusting switching duty cycle through internal feedback control. With a maximum duty cycle of 85%, it accommodates both step-up and step-down operations within a single architecture, making it suitable for systems requiring flexible power conversion from low-voltage sources or high-input rails. This capability ensures consistent performance even under varying supply conditions typical in industrial and embedded applications.
Can the CS51221EDTB16G be used with external synchronous rectifiers to improve efficiency in high-power forward converter designs?
While the CS51221EDTB16G supports transistor driver outputs compatible with external MOSFETs, it does not include an integrated synchronous rectifier controller. Therefore, external rectification must be implemented using discrete components or external drivers. This design choice allows flexibility in selecting rectifier stages based on application-specific efficiency targets and cost constraints, though it increases component count compared to fully integrated solutions.
What are the thermal implications of operating the CS51221EDTB16G at full load across its entire temperature range from -40°C to 85°C?
At sustained full-load operation near 85°C ambient, the device’s junction temperature will rise significantly due to conduction and switching losses inherent in the 1MHz switching frequency. Proper PCB layout with adequate copper pour and thermal vias is essential to maintain safe operating temperatures. Derating may be necessary for continuous high-current applications to ensure long-term reliability and prevent thermal shutdown.
How does the CS51221EDTB16G compare to the NCP1294EDBR2G in terms of switching frequency and control features?
Both the CS51221EDTB16G and NCP1294EDBR2G operate as forward converter controllers with similar topologies, but the CS51221EDTB16G runs at a fixed 1MHz switching frequency, while the NCP1294 typically offers variable frequency modulation for better EMI control. The CS51221 includes built-in soft start, current limit, and ramp control, whereas the NCP1294 emphasizes adaptive burst-mode operation for light-load efficiency—making it more suitable for energy-sensitive applications despite lacking some hard-limit protections found in the CS51221EDTB16G.
Is isolation capability sufficient for use in medical or safety-critical systems with reinforced insulation requirements?
The CS51221EDTB16G is designed to support isolated forward converters when used with appropriate transformer and optocoupler-based feedback networks. However, achieving certified isolation (e.g., IEC 60601) requires additional design validation including creepage, clearance, and transient withstand testing. The controller itself does not provide intrinsic isolation but enables architectures that meet such standards when properly implemented.
What impact does the 1MHz switching frequency have on inductor selection and EMI performance when using the CS51221EDTB16G?
Operating at 1MHz allows smaller magnetics and reduces required inductance values, enabling compact designs. However, higher switching harmonics increase EMI risk, necessitating careful layout, shielding, and filtering. Inductors must exhibit low core losses at 1MHz and maintain saturation margins above peak current. Snubber circuits or spread-spectrum techniques may be needed to pass regulatory emissions tests in sensitive environments.
How does the soft-start feature of the CS51221EDTB16G affect inrush current during startup in capacitive-loaded DC-DC supplies?
The integrated soft-start gradually ramps up the duty cycle upon power-up, limiting peak input current into bulk capacitors. This reduces mechanical stress on input filters and prevents tripping of upstream protection devices. For example, with a 100µF input capacitor and 10ms soft-start time, the average inrush current can be kept below 1.5A even from a 12V rail, minimizing voltage droop and improving system stability during initialization.
Can multiple CS51221EDTB16G units be synchronized via external clock signals to reduce beat frequencies in multi-output systems?
Yes, the CS51221EDTB16G accepts external clock synchronization through its dedicated SYNC pin, allowing master-slave coordination across multiple regulators. This helps decouple switching phases and mitigate intermodulation products that could interfere with sensitive analog circuitry. Proper phase staggering minimizes combined ripple amplitude at the output, enhancing power quality in distributed power architectures.
What considerations apply when substituting the CS51221EDTB16G with alternative parts like the NCP1294EDBR2G in existing reference designs?
Substitution requires verifying compatibility in switching behavior, control loop compensation, and feedback configuration. The NCP1294’s frequency dithering and burst mode introduce different dynamic responses, potentially affecting transient performance and stability margins. Layout-dependent parasitic elements must also be reassessed, especially if the original design relied on the CS51221EDTB16G’s specific slew rate and gate drive characteristics.
How does the absence of serial communication interfaces affect monitoring and diagnostics in automated test equipment using the CS51221EDTB16G?
Lacking digital interfaces means real-time status reporting (e.g., fault detection, overcurrent events) must rely on analog signals such as enable pins, fault flags, or voltage thresholds. This limits remote diagnosis capabilities compared to digitally controllable PMICs, requiring manual intervention or discrete sensing circuits for system-level health monitoring in production test setups.
What trade-offs exist between using the CS51221EDTB16G versus a fully integrated DC-DC module in space-constrained portable devices?
The CS51221EDTB16G offers greater design flexibility and lower BOM cost by offloading passive components to external selection, but consumes more board area than monolithic modules. While it reduces total solution size compared to discrete designs without integration, it still requires careful placement of inductors, capacitors, and transformers, which may negate space savings in ultra-compact form factors.
How does the 85% maximum duty cycle influence minimum achievable output voltage in a step-down configuration with the CS51221EDTB16G?
In step-down mode, the minimum output voltage is constrained by the duty cycle limit. Assuming ideal components and no dropout, the theoretical minimum ratio is approximately (Vout_min / Vin_max) = D_max = 0.85. Thus, with a 15V input, the lowest regulated output would be around 12.75V under this approximation—highlighting limitations for deep step-down ratios without post-regulators.
What precautions should be taken regarding moisture sensitivity when handling the CS51221EDTB16G after opening its packaging?
Although rated MSL 1 (unlimited floor life), best practices dictate storing the CS51221EDTB16G in dry storage (<10% RH) immediately after unpacking to prevent condensation during reflow soldering. If exposed to ambient humidity above 60% RH for extended periods, baking may be required prior to assembly to avoid popcorning or delamination, particularly in lead-free processes exceeding 245°C peak temperature.
How does the single-phase architecture of the CS51221EDTB16G affect scalability in high-current server power supplies?
As a single-output, single-phase controller, the CS51221EDTB16G is inherently limited in delivering multi-amp currents without parallelization or interleaving. Implementing current sharing demands precise matching of external components and tight control loop alignment, increasing complexity. For >20A loads, multi-phase controllers or dedicated POL architectures are typically preferred over single-stage forward converters like those driven by the CS51221EDTB16G.
What role does the ramp signal play in stabilizing the control loop of the CS51221EDTB16G during fast load transients?
The internal ramp generator provides a linear sawtooth waveform referenced to the oscillator, enabling precise slope compensation in peak current-mode control. This stabilizes the inner current loop under high-duty-cycle conditions, preventing subharmonic oscillations during large step-down transitions. Accurate ramp amplitude matching ensures consistent transient response regardless of input or output voltage variations.
Are there any known limitations when cascading the CS51221EDTB16G in multi-stage power architectures involving pre-regulation and post-LDO configurations?
Cascading introduces cumulative phase margin degradation due to added poles from output capacitance and ESR zeros. The CS51221EDTB16G’s fixed-frequency operation complicates compensation across stages, often requiring aggressive damping or reduced bandwidth. Additionally, LDOs downstream may starve of headroom if the forward converter output exceeds LDO dropout unnecessarily, reducing overall efficiency—particularly problematic in battery-powered systems.

Parts with Similar Specifications

The three parts on the right have similar specifications to onsemi CS51221EDTB16G

Product Attribute CS51221EDTB16R2G CS51221ED16G CS51221EDR16G CS51221ED16
Part Number CS51221EDTB16R2G CS51221ED16G CS51221EDR16G CS51221ED16
Manufacturer onsemi onsemi onsemi onsemi
Function - - - -
Frequency - Switching - - - -
Serial Interfaces - - - -
Duty Cycle (Max) - - - -
Base Product Number - DAC34H84 MAX500 ADS62P42
Output Phases - - - -
Package / Case - 196-LFBGA 16-DIP (0.300', 7.62mm) 64-VFQFN Exposed Pad
Mounting Type - Surface Mount Through Hole Surface Mount
Control Features - - - -
Series - - - -
Topology - - - -
Supplier Device Package - 196-NFBGA (12x12) 16-PDIP 64-VQFN (9x9)
Operating Temperature - -40°C ~ 85°C 0°C ~ 70°C -40°C ~ 85°C
Number of Outputs - - - -
Synchronous Rectifier - - - -
Output Type - Current - Unbuffered Voltage - Buffered -
Output Configuration - - - -
Clock Sync - - - -
Voltage - Supply (Vcc/Vdd) - - - -
Package - Tape & Reel (TR) Tube Tape & Reel (TR)

CS51221EDTB16G Datasheet PDF

Download CS51221EDTB16G pdf datasheets and onsemi documentation for CS51221EDTB16G - onsemi.

Datasheets
Cylindrical Battery Holders.pdf
PCN Obsolescence/ EOL
Cylindrical Battery Holders.pdf
Environmental Information
onsemi REACH.pdf onsemi RoHS.pdf

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Customer Reviews

Evaluation: 10 Articles

  • ECUb***h
    Sep 22, 2026

    Used for repair of an older automotive ECU. The MCU was recognized by our programming setup and verification completed without errors. The repaired board now starts and communicates normally.

  • RS48***ieldTech
    Sep 16, 2026

    Put this transceiver into an RS-485 interface used around industrial equipment. Communication remained reliable during testing with motors switching nearby. Good result for the replacement board.

  • Logi***b_Chris
    Sep 8, 2026

    Purchased for a Cyclone III development project. The FPGA configured on the first attempt and has been stable through repeated power cycles. No problems with the I/O we are using.

  • Circ***FixerTom
    Sep 2, 2026

    Used this rectifier in a high-current power supply repair. Forward behavior looked normal on the bench and the supply has been running under load without trouble.

  • Retr***UWorks
    Aug 31, 2026

    Needed the exact ST10F269Z2Q6 for servicing an older control unit. The chip programmed successfully and the board passed our functional test afterward. Much easier than redesigning around a newer MCU.

  • Andr***PCBLab
    Aug 28, 2026

    I needed this ADC for an older data acquisition board. Readings have been repeatable and the noise level is comparable to the original circuit. Happy with the purchase.

  • Leat***O'Keefe
    Aug 20, 2026

    one of my hobbies is skydiving. and when i'm skydiving this works great.

  • Ilen***
    Aug 20, 2026

    This product works considerably well. It secretly improves my basketball by a lot.

  • Indu***ialPower
    Aug 17, 2026

    Installed this IGBT module in a power conversion cabinet. Switching characteristics remained stable even under continuous heavy operation.

  • Nikh***ech
    Aug 13, 2026

    Great low-power MCU for portable equipment. Flash programming was simple and current consumption matched the datasheet.

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CS51221EDTB16G Image

CS51221EDTB16G

onsemi
98D-CS51221EDTB16G

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