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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Voltage Regulators - DC DC Switching Regulators

onsemi FAN53745UC00X

Name: FAN53745UC00X
Brand: onsemi
SKU: FAN53745UC00X
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: FAN53745UC00X

Manufacturer:: onsemi

Category:: Voltage Regulators - DC DC Switching Regulators

Package:: 6-UFBGA, WLCSP

Datasheet:: FAN53745UC00X.pdf

Description:: IC REG BUCK PROG 1A 6WLCSP

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Product details

Overview

FAN53745UC00X from onsemi is a synchronous buck regulator IC delivering 1 A regulated output at 2.5 V, operating from 2.3 V–5.5 V input with 3.33 MHz fixed-frequency PWM and automatic PFM mode transition. It features I²C-programmable output voltage (0.9–3.3 V), programmable current limit (440–2090 mA), internal soft-start, and protection against over-temperature, UVLO, short-circuit, and reverse current - deployed in portable health monitors and RF modules.

For engineers reviewing the FAN53745UC00X datasheet, pinout, applications, or equivalent options, this page delivers verified electrical parameters, WLCSP-6 package layout, I²C interface timing constraints, dynamic voltage scaling behavior, and real-world transient response data for low-power wearable power design.

Technical Context

The FAN53745UC00X implements a proprietary current-mode control architecture with synchronous NMOS/PMOS power switches (RDSON_NMO = 92 mΩ, RDON_PMOS = 125 mΩ) and automatic PFM/PWM mode selection based on load current thresholds (IPFM = 103 mA, IPWM = 135 mA). Its 3.33 MHz switching frequency enables ultra-small external components: 0.47 µH inductor and 4.7 µF input / 2×10 µF output capacitors.

Operation is fully managed via I²C interface (Fast Mode Plus, 1 MHz clock, 10 pF input capacitance), supporting dynamic voltage scaling (0.5–10 mV/s slew rates), hardware reset via SCL hold (>100 ms), and active output discharge with selectable 50 Ω / 100 Ω / 200 Ω pulldown resistors - all within a 1.50 mm × 0.94 mm wafer-level chip-scale package.

Key Specifications

Parameter	Value and Actual Design Meaning
Input Voltage Range	2.3 V to 5.5 V - supports single-cell Li-ion, Li-polymer, and USB-powered systems without pre-regulation.
Output Current	1 A continuous - sufficient for powering ARM Cortex-M cores, BLE radios, and optical sensors in wearables.
Switching Frequency	3.33 MHz (typical) - enables use of sub-1 µH inductors and <10 µF ceramic output capacitors for compact PCB layout.
Output Voltage	2.5 V (factory-programmed) - fixed for FAN53745UC00X; programmable from 0.9 V to 3.3 V in 10–20 mV steps via I²C VSEL register.
I²C Address	7-bit address 0x20 (7h'20) - allows multi-device bus sharing with standard Fast Mode Plus timing (1000 kHz, 120 ns rise/fall).
Current Limit Range	440 mA to 2090 mA - configurable in 110 mA steps to match load requirements and prevent inductor saturation.
Quiescent Current	43 µA (PFM mode, no load) - extends battery life in always-on health monitoring applications.

Pinout & Package

Package: 6-bump Wafer-Level Chip-Scale Package (WLCSP), 0.4 mm pitch, 1.50 mm × 0.94 mm footprint, bottom-side thermal pad (no exposed metal).

Pin/Terminal	Circuit Role	Design Meaning
A1	SDA	I²C bidirectional data line; open-drain, requires external pull-up; must not float.
A2	VIN	Main power input (2.3–5.5 V); place 4.7 µF decoupling capacitor adjacent to this bump.
B1	SCL	I²C clock input; holding low >100 ms triggers hardware reset; must not float.
B2	SW	Switching node connecting to inductor; carries high di/dt; requires tight loop routing to minimize EMI.
C1	FB	Feedback input for output voltage regulation; connects to positive terminal of output capacitor.
C2	GND	Power and signal ground reference; all traces and vias must connect directly to this bump.

Key Features

Feature	Design Value
Automatic PFM/PWM mode transition	Maintains >85% efficiency from 1 mA to 1 A load without manual mode selection or external control logic.
Dynamic Voltage Scaling (DVS)	Programmable 0.5–10 mV/s output ramp rate enables controlled core voltage sequencing in multi-voltage SoCs.
Active output discharge	Selectable 50/100/200 Ω internal pulldown discharges VOUT within milliseconds after shutdown - prevents floating rail issues.
Hardware reset via SCL	Holding SCL low >100 ms resets all registers and clears faults - eliminates need for dedicated reset IC in space-constrained designs.
Reverse current protection	Blocks −1 A negative current in PWM mode and prevents reverse conduction in PFM mode - protects against backfeed from higher-voltage rails.

Applications

Smart Watch Power Management	BLE Radio Supply Regulation
Use Scenario: Regulating battery voltage to supply 2.5 V to an ultra-low-power Bluetooth Low Energy (BLE) transceiver during periodic advertising and connection events. IC Role / Device Role / Timing Role: Primary synchronous buck converter providing dynamically scaled, low-noise 2.5 V rail with fast load transient response (<45 mV deviation at 0→1 A step). Use Value: Enables 3.33 MHz operation to minimize inductor size (0.47 µH), reducing BOM cost and board area while maintaining >90% efficiency at 10 mA average load.	Use Scenario: Delivering stable 2.5 V to a wearable health sensor ASIC that alternates between 10 µA sleep and 500 mA active measurement bursts. IC Role / Device Role / Timing Role: I²C-configurable buck regulator with programmable current limit (1.5 A) and automatic pass-through when VIN approaches VOUT. Use Value: Eliminates need for external LDO post-regulator by sustaining regulation during VIN droop (e.g., 3.0 V → 2.6 V), avoiding brownout during peak sensor current draw.
Optical Heart Rate Module	Energy-Harvesting Sensor Node
Use Scenario: Powering green/red/IR LED drivers and photodiode amplifier in a wrist-based PPG sensor with strict EMI limits. IC Role / Device Role / Timing Role: High-frequency buck converter operating in forced PWM mode to fix switching noise above sensitive analog bands (≥3 MHz). Use Value: 3.33 MHz fundamental frequency places harmonics beyond 10 MHz, easing filtering requirements and reducing conducted emissions into analog front-end circuitry.	Use Scenario: Conditioning variable output from thermoelectric or piezoelectric energy harvester (2.5–4.5 V) to deliver regulated 2.5 V to microcontroller and wireless transmitter. IC Role / Device Role / Timing Role: Wide-input buck regulator with 2.3 V UVLO threshold and 43 µA PFM quiescent current enabling startup from low-energy sources. Use Value: Achieves usable output down to 2.3 V input - critical for harvesting circuits where open-circuit voltage may dip near battery cutoff levels.

Smart Watch Power Management

BLE Radio Supply Regulation

Use Scenario: Regulating battery voltage to supply 2.5 V to an ultra-low-power Bluetooth Low Energy (BLE) transceiver during periodic advertising and connection events.

IC Role / Device Role / Timing Role: Primary synchronous buck converter providing dynamically scaled, low-noise 2.5 V rail with fast load transient response (<45 mV deviation at 0→1 A step).

Use Value: Enables 3.33 MHz operation to minimize inductor size (0.47 µH), reducing BOM cost and board area while maintaining >90% efficiency at 10 mA average load.

Use Scenario: Delivering stable 2.5 V to a wearable health sensor ASIC that alternates between 10 µA sleep and 500 mA active measurement bursts.

IC Role / Device Role / Timing Role: I²C-configurable buck regulator with programmable current limit (1.5 A) and automatic pass-through when VIN approaches VOUT.

Use Value: Eliminates need for external LDO post-regulator by sustaining regulation during VIN droop (e.g., 3.0 V → 2.6 V), avoiding brownout during peak sensor current draw.

Optical Heart Rate Module

Energy-Harvesting Sensor Node

Use Scenario: Powering green/red/IR LED drivers and photodiode amplifier in a wrist-based PPG sensor with strict EMI limits.

IC Role / Device Role / Timing Role: High-frequency buck converter operating in forced PWM mode to fix switching noise above sensitive analog bands (≥3 MHz).

Use Value: 3.33 MHz fundamental frequency places harmonics beyond 10 MHz, easing filtering requirements and reducing conducted emissions into analog front-end circuitry.

Use Scenario: Conditioning variable output from thermoelectric or piezoelectric energy harvester (2.5–4.5 V) to deliver regulated 2.5 V to microcontroller and wireless transmitter.

IC Role / Device Role / Timing Role: Wide-input buck regulator with 2.3 V UVLO threshold and 43 µA PFM quiescent current enabling startup from low-energy sources.

Use Value: Achieves usable output down to 2.3 V input - critical for harvesting circuits where open-circuit voltage may dip near battery cutoff levels.

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous buck regulator applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
TPS6286518RTER	Fixed 1.8 V output, 2.5–5.5 V input, 2 A capability, 4 MHz switching, no I²C interface.	Lacks programmability and DVS; suited for fixed-rail, higher-current applications without voltage sequencing needs.	Choose if output voltage is static and load exceeds 1 A - but requires redesign for I²C-controlled voltage scaling.
RTQ2132BGQW	2.5 V factory-set, 2.3–5.5 V input, 1.2 A, 3 MHz, I²C-compatible with 0x24 address, no DVS or active discharge.	Offers similar quiescent current (45 µA) and package (WLCSP-6), but lacks programmable slew rate and hardware reset.	Prefer when only basic I²C readback (e.g., fault status) is needed - not for dynamic voltage transitions or SCL-triggered recovery.

Compared with TPS6286518RTER and RTQ2132BGQW, the FAN53745UC00X uniquely combines factory-set 2.5 V output with full I²C programmability, 0.5–10 mV/s DVS, active discharge, and SCL hardware reset - making it optimal for wearables requiring adaptive power management and robust fault recovery in minimal footprint.

Availability

FAN53745UC00X is available at Aetrix Electronics and suitable for smart watch power management, BLE radio supply regulation, and optical heart rate module applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for FAN53745UC00X 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

onsemi is a global semiconductor supplier focused on energy-efficient innovation for automotive, industrial, cloud, and IoT applications - delivering high-performance analog, power, and sensing solutions.

The FAN53745UC00X belongs to onsemi's family of ultra-small, I²C-programmable buck regulators designed specifically for space-constrained, battery-powered wearable electronics requiring dynamic voltage scaling and intelligent fault handling.

FAQ

What is the factory-programmed output voltage of the FAN53745UC00X?

The FAN53745UC00X is factory-programmed to deliver 2.5 V output. This value is fixed per the ordering code UC00X and cannot be altered by default configuration; however, the device retains full I²C programmability to reconfigure VOUT between 0.9 V and 3.3 V if required in-system.

Does the FAN53745UC00X support dynamic voltage scaling (DVS)?

Yes, the FAN53745UC00X supports DVS with eight programmable slew rates from 0.5 mV/s to 10 mV/s. Voltage transitions are initiated only upon writing a new value to the VSEL register, and the DVS_EN bit in MODE register (0x03) must be set to enable ramping behavior during both up- and down-scales.

How does the hardware reset function work on the FAN53745UC00X?

The FAN53745UC00X enters hardware reset when the SCL pin is held low for more than 100 ms. During reset, all I²C registers revert to defaults, the buck converter disables, and housekeeping circuitry powers down to reduce consumption. After SCL is released, ~20 µs stabilization is required before issuing new I²C commands.

What protection features are integrated into the FAN53745UC00X?

The FAN53745UC00X integrates over-temperature shutdown, input UVLO (2.15 V rising threshold), output short-circuit detection (triggers immediate fault when VOUT drops below 50% of target), reverse current limiting (−1 A in PWM mode), and open-circuit inductor current limiting - all with status bits accessible via I²C Status Register (0x02).

Can the FAN53745UC00X operate in forced PWM mode?

Yes, the FAN53745UC00X can be forced into PWM mode regardless of load by setting the FORCE_PWM bit in the MODE register (0x03). In FPWM mode, switching remains fixed at 3.33 MHz, ensuring predictable EMI profile and superior load regulation - ideal for noise-sensitive analog circuits like PPG sensors.

FAN53745UC00X Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: 6-UFBGA, WLCSP

Packaging:: Tape & Reel (TR)

Product Status:: Active

Function:: Step-Down

Output Configuration:: Positive

Topology:: Buck

Output Type:: Programmable

Number of Outputs:: 1

Voltage - Input (Min):: 2.3V

Voltage - Input (Max):: 5.5V

Voltage - Output (Min/Fixed):: 1.5V

Voltage - Output (Max):: 3.3V

Current - Output:: 1A

Frequency - Switching:: 3.33MHz

Synchronous Rectifier:: Yes

Operating Temperature:: -25°C ~ 85°C (TA)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 6-WLCSP (1.38x0.94)

FAN53745UC00X FAQ

1.How can I place an order for FAN53745UC00X through Aetrix?

Please submit a Request for Quotation (RFQ) for FAN53745UC00X 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 FAN53745UC00X reliable?

The price and inventory of FAN53745UC00X are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for FAN53745UC00X is usually 5 days.

3.What payment methods are accepted for FAN53745UC00X?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for FAN53745UC00X transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for FAN53745UC00X?

FAN53745UC00X orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your FAN53745UC00X 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 FAN53745UC00X?

For technical support, including FAN53745UC00X datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your FAN53745UC00X requirements.

6.How does Aetrix verify that FAN53745UC00X is sourced from the original manufacturer or authorized distributors?

All FAN53745UC00X 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 FAN53745UC00X meets industry standards.

7.What is the process for return or replacement of FAN53745UC00X?

All FAN53745UC00X units undergo pre-shipment inspection (PSI). If there is an issue with FAN53745UC00X, 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 FAN53745UC00X part is unused and in its original packaging.

Return procedure for FAN53745UC00X:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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