Portable electronics rarely run out of battery because peak current is too high. More often, capacity is lost quietly over time. Sensors stay powered, regulators remain active, and background rails never truly switch off. In compact wearables and handheld devices, those steady losses tend to dominate real-world battery life. That is the operating reality Diodes Incorporated is targeting with the AP61040 and AP61041, two small synchronous buck converters designed for low-current rails that must remain efficient long after the system has gone idle.
Rather than focusing on headline output current, these devices are intended for supply domains that sit between always-on and frequently active. Microcontrollers, sensor hubs, and housekeeping logic all fall into this category. With a 400 mA output rating and very low internal consumption, the AP61040 and AP61041 are positioned to support those rails without becoming a meaningful load themselves.
Quiescent Losses in Always-Powered Rails
In many portable designs, regulators spend far more time supplying tens of milliamps than hundreds. At that point, quiescent current becomes as important as conversion efficiency under load. The AP61040 and AP61041 are designed to keep that background loss low enough that it does not erode battery capacity over long idle periods.
What makes this relevant is not a single operating point, but consistency. These converters maintain regulation accuracy as load current rises and falls, avoiding the behaviour seen in some low-IQ devices where response degrades once the system wakes. For engineers, that stability simplifies power budgeting, particularly in designs where subsystems cycle frequently between sleep and active states.
Constant On-Time Control Across Battery Voltage Range
The control scheme plays a significant role in how the converters behave as conditions change. Both devices use constant on-time control, which is well suited to applications with wide input-to-output voltage ratios. In practice, this allows fast response to line and load transients without relying on complex compensation networks or large external components.
One consequence of this approach is how the converters behave near dropout. As battery voltage approaches the regulated output, the devices transition smoothly into 100 percent duty cycle operation rather than encountering an abrupt regulation limit. For battery-powered products that are expected to run cells deep into discharge, this behaviour helps avoid early brownouts and unpredictable resets.
Output Voltage Selection and Design Reuse
The AP61040 and AP61041 differ primarily in how output voltage is configured. The AP61040 offers three selectable output voltages from 0.6 V to 3.3 V using a single selection pin, prioritising simplicity and minimal configuration. The AP61041 provides two VSEL pins, enabling programmable feedback across the same voltage range.
This split gives designers flexibility at the platform level. A fixed-voltage rail and a programmable rail can be implemented using closely related devices, which reduces qualification effort when building product variants or supporting multiple subsystems from a common design approach.
Board Area, Protection, and Thermal Practicalities
At the board level, the converters are intended to be straightforward to integrate. Operation is optimised around a 2.2 µH inductor and 10 µF input and output capacitors, keeping the external component count low and predictable. That matters in dense layouts where power circuitry competes for space with radios, sensors, and processors.
Protection features are integrated rather than external. Undervoltage lockout, overcurrent protection, and overtemperature protection are all built in, reducing the need for additional circuitry in systems that may see wide temperature variation or uncertain loading. The devices are supplied in a 1.17 mm by 0.77 mm six-ball WLB package, allowing placement close to the load and helping limit parasitic losses in compact designs.
Incremental Power Improvements That Add Up
The AP61040 and AP61041 reflect a broader trend in portable power design. Instead of chasing higher peak performance, manufacturers are refining behaviour in the operating regions that dominate real usage. Lower background losses, predictable transient response, and simple integration all contribute more to usable battery life than marginal gains at full load.
For engineers, the takeaway is familiar. In small battery-powered systems, the quiet losses matter most. Devices that address those losses directly tend to deliver the biggest system-level gains.
Learn more and read the original announcement at www.diodes.com
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