Overview

The MIC29302WU (MIC29302) is a 3A high-current, ultra-low dropout (LDO) adjustable linear voltage regulator manufactured by Microchip Technology (originally Micrel Semiconductor). Housed in a surface-mount TO-263-5 (D2PAK) package (or through-hole TO-220-5 as MIC29302WT), it provides clean, adjustable output voltages from $1.24\text{V}$ to $26\text{V}$ with an extraordinarily low typical dropout of only $370\text{ mV}$ at full $3.0\text{A}$ load ($250\text{ mV}$ at $1.5\text{A}$).

Using Micrel's proprietary Super βeta PNP process, the MIC29302 delivers high output current without the severe $1.5\text{V} \dots 2.5\text{V}$ dropout penalty of classic regulators like the LM317 or LM7805. Featuring a TTL-compatible ENABLE control pin for zero-current shutdown mode, reverse-battery protection, and thermal limiting, it is widely utilized for high-power FPGA/SDR core supplies, cellular/GSM modem power rails (which require high pulsed 2A–3A currents with minimal voltage sag), post-regulators for SMPS, and high-current battery chargers.

Quick reference

Pinout (TO-263-5 / TO-220-5 Package)

Looking at the package from the front with pins pointing down:

        ┌──────────────┐
        │   TO-263-5   │
        │  MIC29302WU  │
        └─┬──┬───┬──┬──┘
          1  2   3  4  5
         EN VIN GND VOUT ADJ

Specifications

Voltage Setting Calculation

The output voltage is configured with a two-resistor divider between VOUT, ADJUST, and GND:

$V_{OUT} = V_{REF} \times \left(1 + \frac{R_1}{R_2}\right) = 1.240\text{V} \times \left(1 + \frac{R_1}{R_2}\right)$

• Set $R_2 \approx 10\text{ k}\Omega$ (so the divider current is $\approx 124\ \mu\text{A}$, minimizing bias current error).
• For $V_{OUT} = 3.3\text{V}$: $R_2 = 10\text{ k}\Omega \implies R_1 = 16.6\text{ k}\Omega$ (use standard $16.5\text{ k}\Omega$ 1%).
• For $V_{OUT} = 5.0\text{V}$: $R_2 = 10\text{ k}\Omega \implies R_1 = 30.3\text{ k}\Omega$ (use standard $30.1\text{ k}\Omega$ 1%).

Typical Application Circuit

  Unregulated DC In (e.g. 5V or 12V)
           │
           ├───[ C_IN: 10µF Tantalum/Electrolytic ]───┐
           │                                          │
       [Pin 2: INPUT]                                 │
      MIC29302WU                                      │
  MCU ─[Pin 1: ENABLE]                                │
       [Pin 3: GROUND] ───────────────────────────────┼─── Common System GND
       [Pin 4: OUTPUT] ────┬──────────────────────────┤
           │               │                          │
           │             [ R1: 16.5kΩ ]               │
           │               │                          │
           │               ├──► [Pin 5: ADJUST]       │
           │               │                          │
           │             [ R2: 10kΩ ]                 │
           │               │                          │
           ├───[ C_OUT: 22µF - 47µF (ESR > 0.05Ω) ]───┘
           │
  Regulated +3.3V DC Output (Up to 3.0A High-Current Rail)

Capacitor Stability Requirements

• Output Capacitor: The MIC29302 requires an output capacitor of $\ge 10\ \mu\text{F}$ (recommend $22\ \mu\text{F} \dots 47\ \mu\text{F}$) between OUTPUT and GROUND.
• ESR Considerations: The ESR must be between $0.05\ \Omega$ and $2.0\ \Omega$. If using ceramic MLCC output capacitors, add a small $0.22\ \Omega$ series resistor to ensure LDO control loop phase margin stability.

Common mistakes

• Leaving the ENABLE pin floating: The ENABLE pin has internal high impedance. Leaving it disconnected may cause erratic shutdown/startup behavior. Tie directly to INPUT (VIN) for always-on operation.
• Neglecting PCB thermal dissipation at 3A: At $3\text{A}$ load with $1.5\text{V}$ voltage drop ($V_{IN} - V_{OUT}$), power dissipation is $4.5\text{ Watts}$. Ensure ample PCB copper ground plane area is connected to the TO-263 tab.

Notes

• Suffix Identification: "WU" designates TO-263-5 (D2PAK) surface mount; "WT" designates TO-220-5 through-hole package.