ortable / Battery LDO: UVLO & Ultra-Low Off Leakage

Introduction & Scope

When an LDO is fed directly from a battery, three parameters dominate the design: VIN coverage (to match the chemistry), a stable UVLO window (to avoid chatter at end-of-life), and ultra-low off leakage (so the device does not self-drain during storage or shipping).

This page focuses on portable / battery-powered rails such as wearables, handheld meters, data loggers, and single-cell devices. It does not cover: high-PSRR audio/RF LDOs, LED bias LDOs, DDR VTT/Vref regulators, or high-voltage automotive front-end LDOs. Those belong to their own subpages in the LDO hub to keep Google from seeing overlapping content.

For procurement and cross-brand substitution, the key is to always request/record three numbers in the BOM note: 1) VIN(min/max), 2) UVLO(on/off + hysteresis), 3) EN=LOW off-leakage. Many datasheets publish Iq but omit Ioff.

Battery Chemistries & VIN Mapping

Different battery chemistries sit at different voltage plateaus and have different end-of-life behaviors. A portable LDO should therefore be chosen by chemistry → VIN(min/max) → transient headroom, not by a single “2.5–5.5 V” headline.

Below is a compact mapping for four common sources: 1S Li-ion/Poly, 1S LiFePO4, 2×AA/AAA, and 3.6 V primary lithium. For each, the LDO needs a lower VIN floor to avoid early dropout, and a sensible UVLO ON/OFF pair to prevent chatter when the battery is almost empty.

Note: 2×AA/AAA sources are the most likely to trigger UVLO chatter because of internal resistance. Always test under real load, not only with a bench supply.

UVLO & Hysteresis Design

In battery-direct rails, UVLO is not only a start/stop threshold. It must tolerate cold batteries, connector bounce, and short high-current bursts. Always record UVLO ON, UVLO OFF, and hysteresis in the BOM note so that cross-brand replacements from TI, ST, NXP, Renesas, onsemi, Microchip, or Melexis can match the same behavior.

A practical target for portable devices is hysteresis ≥ 300 mV. This margin absorbs cable/connector spikes, small battery rebounds, and slow soft-start ramps. Without enough hysteresis, the LDO may chatter close to end-of-life battery voltage and generate audible or visible flicker in the system.

UVLO must also be verified over temperature (for example, −20 °C, 25 °C, 60 °C). Low-temperature Li-ion cells drop their voltage faster; a fixed UVLO without temperature margin can shut down too early. If the LDO allows external resistor-programmed UVLO, this is the best way to tune it per battery chemistry.

Tip: test UVLO with a real battery emulator or with series resistance to emulate aged/cold cells. Bench supplies without series R will hide chatter risks.

Shutdown Off-Leakage & Load Disconnect

For portable equipment that is shipped, stocked, or stored for months, the LDO must show near-zero off-leakage when EN=LOW. A good target is < 100 nA for the LDO itself, and < 1–5 µA for the whole board. If the datasheet does not state Ioff, request it before issuing the PO.

Also check whether the device provides true load-disconnect. Some LDOs only disable the internal pass element, but still allow a small backfeed from VOUT to VIN or through ESD/sense paths. In those cases, pair the LDO with a small external load switch (preferably automotive/industrial grade) to achieve real isolation.

When output discharge is enabled, VOUT is pulled down on shutdown to prevent false wake-ups in the load. However, this circuit can contribute to off-leakage, so it must be measured at 25 °C, −20 °C, and 60 °C and recorded in the BOM comments for future cross-brand alternatives.

Measure EN=LOW leakage at three temperatures and write it into the BOM note. This makes cross-brand replacement safer for small-batch buyers.

Dropout vs Battery Discharge

The dropout voltage is not just the difference between input and output voltages at full load. It also includes the impact of low temperature and battery aging, which cause an increase in internal resistance and a faster voltage drop. Ensure dropout voltage is ≥ 100–300 mV above the minimum battery voltage.

For portable devices, consider both full-load dropout and the efficiency drop as the battery voltage decreases. Additionally, at low temperatures, the internal resistance of the battery increases, which leads to higher voltage drops.

It’s essential to test the LDO’s performance at low temperature and with aged batteries to ensure it can handle real-world conditions, where voltage drop and efficiency will be impacted by aging and temperature effects.

Reverse Current & Ship Mode

Reverse current blocking (RCB) prevents unwanted current flow when the LDO is disabled. In some cases, external load switches are needed to provide complete isolation and prevent backfeed. LDOs with true load-disconnect can also achieve this functionality.

For transport and storage modes, ensure the LDO or external circuit operates in ship mode to minimize current consumption (< 1 µA is ideal). This is especially important for devices that may be stored for extended periods before use.

Additionally, for systems with RTC or keep-alive functions, these must be bypassed from the main power rail to allow the LDO to stay in a low-power shutdown state while still keeping vital functions running.

Protection & Reliability

In portable LDOs, protection features are crucial for ensuring safe and reliable operation under various conditions. Key features include overcurrent protection, short-circuit protection, thermal shutdown, and ESD protection, all of which safeguard the LDO and the device it powers.

Overcurrent and short-circuit protection prevent excessive current that could damage the device, while thermal shutdown ensures the device doesn’t overheat during heavy loads. Additionally, ESD protection is essential for preventing static discharge damage, especially in hand-held or portable devices.

The thermal resistance of the LDO package plays a critical role in the performance and longevity of the device, especially in hand-held applications where heat dissipation may be limited. Be sure to check both the thermal shutdown threshold and thermal resistance (RθJA) values to ensure reliable operation in your specific application.

Validation Playbook

Validating LDO performance in real-world conditions is critical. Follow these steps for comprehensive testing:

1. **Off-leakage measurement**: Test the leakage current when EN=LOW across three temperature points (e.g., −20°C, 25°C, 60°C). Ensure the leakage is within acceptable limits (< 100 nA).

2. **UVLO step scan**: Perform a step scan by gradually decreasing the input voltage and recording the UVLO on/off thresholds to ensure the device responds as expected.

3. **Cold/hot box testing**: Verify LDO performance at low and high temperatures to ensure stable operation in extreme environments.

4. **Connector bounce reproduction**: Test the system under real mechanical conditions to ensure UVLO has adequate debounce for connector or button presses.

5. **Long-duration static power consumption logging**: Use a power analyzer to log power consumption during standby mode and over extended periods.

IC Selection Checklist

The following checklist summarizes the critical parameters to verify when selecting a portable LDO for battery-direct applications:

Ensure the LDO meets the following selection criteria:

• Input Voltage Range: Make sure it covers the full range of the battery (e.g., 1S Li-ion, 2×AA, etc.).
• UVLO ON/OFF: Ensure the LDO has appropriate UVLO thresholds (ON = 3.0 V, OFF = 2.7 V).
• Off-Leakage: For portable devices, target leakage < 100 nA when EN = LOW.
• Thermal Resistance (RθJA): Make sure the LDO has a low thermal resistance to handle heat dissipation in hand-held applications.
• Dropout Voltage: Verify dropout voltage at full load and low temperatures.

Mini IC-Selection

Below is a framework for selecting specific LDO part numbers based on the fields from the IC Selection Checklist. As you proceed, ensure that all the critical parameters like UVLO, Ioff, thermal resistance, and dropout are filled in with the exact part numbers from the manufacturers you are considering.

This framework will help you compare models from the seven major manufacturers (TI, ST, NXP, Renesas, onsemi, Microchip, and Melexis).

FAQ / PAA (15)

Below are the most common questions regarding portable LDOs. These FAQs address the selection and testing processes specific to LDOs in battery-direct applications.