Technical Information Site of Power Supply Design

Product Key Points

BD9S Series: Ultra-small Step-down DC/DC Converters for Automotive, ADAS Applications with Power-good Pin

Wettable-Flank QFN Package Adopted in
2A/3A/4A Versions with SLLM™ Control

  • ADAS (Advanced Driver Assistance System)
  • BD9S series
  • Power Good
  • Adjustable soft start
  • AEC-Q100 grade 1
  • 2.2 MHz
  • Compact inductor
  • BD9S400MUF-C
  • BD9S300MUF-C
  • BD9S200MUF-C
  • SLLM
  • PWM
  • PFM
  • Wettable-flank package
  • BD9S100NUX-C
  • BD9S000NUX-C

ROHM recently announced the "BD9S Series" of secondary step-down DC/DC converters, intended for use in safe driving assistance modules of automobiles such as ADAS (Advanced Driver Assistance Systems) sensors, cameras, radars and the like, in which compactness, low power consumption, and high reliability are required.

The "BD9S series" are miniaturized high-efficiency single-channel synchronous rectification step-down DC/DC converters provided with power good and adjustable soft start functions, and are compliant to AEC-Q100 grade 1 for automotive applications. A power good signal is output as a flag to indicate whether the output voltage is within a preset tolerance range, in order to enhance system stability and reliability. Adjustable soft start can be set using one capacitor, providing a high degree of freedom and enabling safe startup by preventing inrush currents on startup and the like. 2.2 MHz is used as the switching frequency to avoid interference with AM radio, and at the same time a compact inductor can be used. These features, together with the small-size package, contribute to miniaturization of the power supply circuit.

The new products have internal power MOSFETs. Newly released are two series: the 4 A output BD9S400MUF-C, 3 A BD9S300MUF-C, and 2 A BD9S200MUF-C with Nch+Nch configurations and adopting 3×3 mm wettable-flank QFN packages, and the 1 A BD9S100NUX-C and 0.6 A BD9S000NUX-C, with Pch+Nch configurations in 2×2 mm packages. These devices have adjustable outputs; fixed-output counterparts are currently in development. The following table lists the BD9S series.

Part No. Output
Package Common Specifications
BD9S400MUF-C 0.8V~Vin×0.8V 4.0A VQFN16FV3030
・Input voltage range: 2.7 V to 5.5 V
・Output voltage accuracy: ±1.5%
・Switching frequency:
   2.2 MHz±0.2 MHz
・Operating temp. range:
   –40°C to 125°C
BD9S300MUF-C 3.0A
BD9S200MUF-C 2.0A
BD9S100NUX-C 0.8V~Vin 1.0A VSON008X2020
BD9S000NUX-C 0.6A
**BD9S110NUX-C 1.2V 1.0A Same as above
**BD9S111NUX-C 1.8V 1.0A

** The BD9S110NUX-C and the BD9S111NUX-C are currently in development.

Features of the 4 A/3 A/2 A Version Products BD9S400MUF-C/BD9S300MUF-C/BD9S200MUF-C

The models BD9S400MUF-C/BD9S300MUF-C/BD9S200MUF-C, rated at 4, 3, and 2 A respectively, are configured with internal Nch output-stage power MOSFETs on both the high and the low sides. Features are summarized below. Boldface indicates features present only in the models BD9S400MUF-C/BD9S300MUF-C/BD9S200MUF-C.

Nch+Nch synchronous rectifying step-down DC/DC converter
3×3 mm Wettable-flank
QFN package
SLLM control and forced PWM mode
External switching frequency synchronization function
Flexible external phase compensation
Wettable-flank QFN package
・AEC-Q100 grade 1 compatible
・2.2 MHz PWM current mode operation
・Adjustable soft start function: Set with one capacitor
・Power Good output (Nch open drain)
・Enable control
・Various protection functions: Input undervoltage lockout (UVLO), load short-circuit protection (SCP)function, output overvoltage protection (OVP) function, Overcurrent protection (OCP) function, thermal shutdown (TSD) function

BD9S400MUF-C Block Diagram (Click to enlarge)

BD9S400MUF-C: Example of Efficiency Curve at 5Vin/3.3Vout

■SLLM Control
SLLM (Simple Light Load Mode) is ROHM's unique function for maintaining high efficiency under light loading, and is already adopted in numerous models.
During light loading, switching is automatically performed from fixed-frequency PWM operation to PFM operation. Moreover, a MODE/SYNC pin can be used to set a forced PWM mode, in which SLLM switching does not occur.

■Wettable-Flank Packages
A wettable-flank package is a package that enables visual check of the soldered state, which for QFN and other leadless packages cannot easily be determined from the appearance. In automotive applications, 100% visual inspections of soldered states are required, and so in recent years wettable-flank packages have attracted much attention.

The 1 A/0.6 A BD9S100NUX-C/BD9S000NUX-C models, in 2×2 mm packages with a Pch+Nch configuration, are described in a separate article.

Power Supply Design Technical Materials Free Download

Power Supply Design Technical Materials Free Download

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