MIC5235-5.0YM5-TR

The MIC5235-5.0YM5-TR from Microchip Technology is a 5.0 V fixed output, ultra-low quiescent current LDO linear regulator designed for battery-powered and USB-powered applications that require a wide input voltage range and minimal ground current.

The defining characteristic of the MIC5235 is the combination of ultra-low ground current (18 uA at light load) and wide input voltage range (up to 24 V). This makes it uniquely suited for applications where a 5 V rail must be maintained from a high-voltage, variable, or slowly-discharging battery source. Typical use cases include 3-cell Li-Ion battery packs (9-12.6 V), 12 V automotive battery, 24 V industrial supplies, and USB bus power.

The 18 uA ground current at light load is one of the lowest in the industry for a 24 V LDO. In battery-powered applications that spend most of their time in standby, the ground current of the regulator dominates the battery drain. A typical LDO with 500 uA ground current would drain a 1000 mAh battery in about 83 days (standby only), while the MIC5235 with 18 uA would take over 2300 days. This 28x improvement in standby battery life is the key value proposition.

The 24 V maximum input voltage is significantly higher than most LDOs in the SOT-23-5 package (typically limited to 6-10 V). This high input rating allows the MIC5235 to be used directly from 12 V automotive or 24 V industrial supplies without a preregulator, reducing component count and cost. The absolute maximum input voltage is 38 V, providing comfortable margin for automotive load dump transients when combined with external transient suppression.

The microCap design means the MIC5235 is stable with only a 2.2 uF output capacitor, and it is compatible with both ceramic (X5R, X7R) and tantalum capacitors. The use of a ceramic output capacitor is preferred for its low ESR, small size, and lack of aging degradation. The minimum 2.2 uF value is small enough to fit in a 0603 or 0805 package, minimizing board space.

The 5.0 V fixed output is the most common voltage for USB-powered devices and many sensor interface standards. The plus or minus 2 percent accuracy over temperature ensures the output remains within 4.9-5.1 V, well within the USB voltage specification (4.75-5.25 V at the device) when accounting for trace resistance.

The enable (EN) pin allows the regulator to be turned off by a microcontroller GPIO, reducing system standby current to essentially zero (0.1 uA typical). This is critical for applications with strict off-state current budgets, such as battery-powered devices that must meet ENERGY STAR or similar standby power requirements.

The reverse battery protection feature prevents damage if the input supply is connected with reversed polarity. The reverse leakage protection prevents current from flowing from the output back to the input when the input voltage is lower than the output voltage (e.g., when the input supply is removed while the output capacitor is still charged). Both protections eliminate the need for external protection diodes in most applications.

The MIC5235-5.0YM5-TR is part of the MIC5235 family, which also includes other fixed voltage options (1.8 V, 2.5 V, 3.0 V, 3.3 V) and an adjustable version (1.24 V to 20 V, part number MIC5235YM5-TR). All variants share the same SOT-23-5 pinout and electrical characteristics, differing only in output voltage. The -5.0 variant is the most popular for USB and 5 V logic applications.

At $0.62 per unit in volume (1000+), the MIC5235-5.0YM5-TR is cost-competitive with other 24 V LDOs, most of which have higher ground current or lack the enable and reverse protection features.

The MIC5235-5.0YM5-TR operates as a PNP pass transistor based low dropout linear regulator with a precision voltage reference and error amplifier.

PNP Pass Transistor: Unlike LDOs that use a PMOS pass transistor, the MIC5235 uses a PNP bipolar transistor as the pass element. The PNP transistor allows the regulator to operate with very low input-output voltage differential (dropout voltage). The dropout voltage of a PNP-based LDO is approximately VCE(sat) of the PNP transistor plus the current sense resistor voltage drop, which at 150 mA is only 310 mV. The PNP topology also enables the wide input voltage range (up to 24 V) because the PNP collector-base junction can withstand high voltages. However, the PNP transistor requires base current that adds to the ground current, which is why the ground current increases with load current (from 18 uA at light load to 2 mA at 150 mA full load).

Error Amplifier and Reference: The error amplifier compares a fraction of the output voltage with the internal 1.24 V bandgap reference. For the fixed 5.0 V version, the feedback divider is internal and trimmed at the factory to set the output voltage. The error amplifier drives the base of the PNP pass transistor to maintain regulation. The high DC gain of the error amplifier (typically 60-80 dB) ensures excellent line and load regulation (0.04 percent and 0.25 percent respectively).

Dropout Operation: When the input voltage drops to within the dropout voltage of the output (VIN less than VOUT + 310 mV at 150 mA), the PNP pass transistor enters saturation. In saturation, the regulator can no longer maintain regulation because the pass transistor is fully on (minimum VCE). The output voltage tracks the input voltage minus the dropout voltage. The dropout voltage is proportional to load current: VDO = IOUT x RDS(equivalent) approximately. At lower currents, the dropout voltage is much less (50 mV at 100 uA, 230 mV at 50 mA).

Ground Current: The ground current (also called quiescent current or Iq) has two components: the bias current for the internal circuitry (amplifier, reference, protection circuits) and the PNP base drive current. At light load (IOUT = 100 uA), the total ground current is only 18 uA, dominated by the bias current. As the load increases, the PNP base current increases proportionally (beta-limited), reaching 2 mA at 150 mA load. In shutdown mode (EN = LOW), all internal bias is disabled and the ground current drops to less than 1 uA.

Enable Circuit: The EN pin is a CMOS-compatible logic input. When EN is HIGH (above 2.0 V), the regulator is enabled and operates normally. When EN is LOW (below 0.6 V), the regulator is disabled; the PNP pass transistor is turned off, the error amplifier is shut down, and the reference is disabled. The EN pin input current is very low (0.01 uA typical when HIGH), allowing it to be driven directly by a microcontroller GPIO or a pull-up resistor. The EN pin is not referenced to VIN; it has its own absolute maximum rating (38 V).

Reverse Battery Protection: When the input voltage is negative (reversed polarity), the internal circuitry prevents the PNP pass transistor from conducting, and the body diode paths are blocked. The output leakage in reverse polarity is specified as -0.1 uA maximum at VIN = -15 V, meaning essentially no current flows in the wrong direction.

Reverse Leakage Protection: When VIN is lower than VOUT (e.g., input supply removed, output capacitor still charged), the PNP pass transistor blocks reverse current from flowing from VOUT to VIN. This is different from PMOS-based LDOs where the body diode can conduct reverse current. The reverse leakage protection eliminates the need for an external blocking diode.

Thermal Shutdown: The thermal shutdown circuit monitors the die temperature and turns off the pass transistor when the junction temperature exceeds approximately 150 degrees C. When the junction cools below the thermal shutdown hysteresis threshold (approximately 130 degrees C), the regulator restarts. In the SOT-23-5 package with 235 degrees C/W thermal resistance, the maximum power dissipation at 25 degrees C ambient is approximately 319 mW (calculated as (125 – 25) / 235 = 426 mW, derated for safety). For high VIN-VOUT differentials, the output current must be limited to keep power dissipation within the package capability.

Current Limit: The current limit circuit monitors the output current and limits it to approximately 350 mA typical (500 mA maximum) when a short circuit is detected. The current limit protects the pass transistor from damage but does not prevent the junction temperature from rising; thermal shutdown provides the secondary protection layer.