AOZ1282CI — 1.2 A Simple Buck Regulator

**Source:** [Alpha & Omega AOZ1282CI Datasheet](https://www.aosmd.com/res/data_sheets/AOZ1282CI.pdf)
**Manufacturer:** Alpha & Omega Semiconductor
**Part Number:** AOZ1282CI
**Document:** Rev 1.4 — June 2022 (EZBuck™ 1.2 A Simple Buck Regulator)

## Description

The AOZ1282CI is a high-efficiency, simple-to-use 1.2 A buck regulator flexible enough to be optimized for a variety of applications. The AOZ1282CI works from a 4.5 V to 36 V input voltage range and provides up to 1.2 A of continuous output current. The output voltage is adjustable down to 0.8 V. The fixed switching frequency of 450 kHz PWM operation reduces inductor size.

## Key Specifications

| Parameter | Value |
| --- | --- |
| Input Voltage Range | 4.5 V – 36 V |
| Output Current | 1.2 A continuous |
| Output Voltage | Adjustable down to 0.8 V |
| Switching Frequency | 450 kHz (fixed PWM) |
| Internal NMOS R<sub>DS(on)</sub> | 420 mΩ |
| Efficiency | Up to 95 % |
| Package | SOT23-6L |
| Operating Temperature | −40 °C to +85 °C (ambient) |

## Features

- 4.5 V to 36 V operating input voltage range
- 420 mΩ internal NMOS
- Up to 95 % efficiency
- Internal compensation
- 1.2 A continuous output current
- Fixed 450 kHz PWM operation
- Internal soft start
- Output voltage adjustable down to 0.8 V
- Cycle-by-cycle current limit
- Short-circuit protection
- Thermal shutdown
- Small-size SOT23-6L package

## Applications

- Telecom / Networking / Datacom equipment
- Point-of-load DC/DC conversion
- Set-top boxes and cable modems
- DVD drives and HDDs
- LCD monitors and TVs

## Pin Configuration

Package: SOT23-6L (Top View).

| Pin | Name | Function |
| --- | --- | --- |
| 1 | BST | Bootstrap Voltage Input. High-side driver supply. Connect a 100 nF capacitor between BST and LX. |
| 2 | GND | Ground |
| 3 | FB | Feedback Input. Regulated to 0.8 V. Used to set the PWM output voltage via a resistor divider between the output and GND. |
| 4 | EN | Enable Pin. Active high. Connect EN pin to VIN through a current-limiting resistor. Do not leave EN floating. |
| 5 | VIN | Supply Voltage Input. 4.5 V to 36 V. When VIN rises above the UVLO threshold, the device starts up. |
| 6 | LX | PWM Output. Connect to inductor. |

## Absolute Maximum Ratings

Exceeding the Absolute Maximum Ratings may damage the device.

| Parameter | Rating | Units |
| --- | --- | --- |
| Supply Voltage (V<sub>IN</sub>) | 40 | V |
| LX to GND | −0.7 to V<sub>IN</sub>+0.3 | V |
| LX to GND transient, < 10 ns | −3 | V |
| EN to GND | −0.3 to 40 | V |
| FB to GND | −0.3 to 6 | V |
| BST to GND | V<sub>LX</sub> + 6 | V |
| Junction Temperature (T<sub>J</sub>) | +150 | °C |
| Storage Temperature (T<sub>S</sub>) | −65 to +150 | °C |
| ESD Rating (HBM, 1.5 kΩ + 100 pF) | 2 | kV |

## Recommended Operating Conditions

| Parameter | Rating |
| --- | --- |
| Supply Voltage (V<sub>IN</sub>) | 4.5 V to 36 V |
| Output Voltage (V<sub>OUT</sub>) | 0.8 V to 0.85×V<sub>IN</sub> |
| Ambient Temperature (T<sub>A</sub>) | −40 °C to +85 °C |
| Package Thermal Resistance (θ<sub>JA</sub>) | 220 °C/W (SOT23-6L) |

## Electrical Characteristics

T<sub>A</sub> = 25 °C, V<sub>IN</sub> = 12 V, unless otherwise specified. **Bold** indicates temperature range of −40 °C to +85 °C.

| Parameter | Symbol | Conditions | Min | Typ | Max | Units |
| --- | --- | --- | --- | --- | --- | --- |
| Supply Voltage | V<sub>IN</sub> | | **4.5** | | **36** | V |
| Input Under-Voltage Lockout Threshold | V<sub>UVLO</sub> | V<sub>IN</sub> rising / falling | **2.3** | 2.9 | | V |
| UVLO Hysteresis | V<sub>UVLO_HYS</sub> | | | 260 | | mV |
| Quiescent Supply Current | I<sub>IN</sub> | I<sub>OUT</sub> = 0, FB = 1 V, EN > 1.2 V | | 1 | **1.5** | mA |
| Shutdown Supply Current | I<sub>OFF</sub> | EN = 0 V | | | **8** | µA |
| Feedback Voltage | V<sub>FB</sub> | | 784 | 800 | 816 | mV |
| Load Regulation | V<sub>FB_LOAD</sub> | 0.12 A < Load < 1.08 A | | 0.5 | | % |
| Line Regulation | V<sub>FB_LINE</sub> | Load = 600 mA | | 0.03 | | %/V |
| FB Input Current | I<sub>FB</sub> | FB = Regulation | | | 500 | nA |
| EN Input Threshold (Off) | V<sub>EN_OFF</sub> | Off threshold | | | **0.4** | V |
| EN Input Threshold (On)  | V<sub>EN_ON</sub>  | On threshold  | **1.2** | | | V |
| EN Input Hysteresis | V<sub>EN_HYS</sub> | | | 200 | | mV |
| EN Input Current | I<sub>EN</sub> | | | | **3** | µA |
| Switching Frequency | f<sub>O</sub> | | 360 | 450 | 540 | kHz |
| Maximum Duty Cycle | D<sub>MAX</sub> | | | 87 | | % |
| Minimum On Time | t<sub>ON_MIN</sub> | | | 150 | | ns |
| Current Limit | I<sub>LIM</sub> | | 1.5 | 1.9 | | A |
| Thermal Shutdown Limit (T<sub>J</sub> rising) | T<sub>SD</sub> | | | 150 | | °C |
| Thermal Shutdown Limit (T<sub>J</sub> falling) | | | | 110 | | °C |
| Soft-Start Interval | t<sub>SS</sub> | | | 1.5 | | ms |
| NMOS Leakage | I<sub>LEAKAGE</sub> | EN = 0, LX = 0 | | | 10 | µA |
| NMOS On-Resistance | R<sub>DS(on)</sub> | | | 420 | | mΩ |

## Key Formulas

Feedback divider sets output voltage:

$$V_{OUT} = 0.8\text{ V} \times \left(1 + \frac{R_1}{R_2}\right)$$

Output capacitor ripple (low-ESR ceramic):

$$\Delta V_{OUT} \approx \frac{\Delta I_L}{8 \times f \times C_O}$$

Total power dissipation (conduction-loss dominated):

$$P_{total\_loss} = (V_{IN} \times I_{IN}) - (V_{OUT} \times V_{IN})$$

## Applications

- Typical application: the Figure 1 reference circuit uses an external inductor L, output capacitor C<sub>2</sub>, bootstrap capacitor C<sub>3</sub>, and feedback resistors R<sub>1</sub>/R<sub>2</sub>. Enable pin should be driven by VIN through a current-limiting resistor.
- Output-capacitor selection: use ceramic (X5R/X7R) capacitors for low ESR and tight ripple; low-ESR tantalum or aluminum electrolytic also work.
- Layout: the two high-current loops — input path VIN→C₁→switch and output path LX→L→C<sub>OUT</sub>→Schottky — should both be kept tight to minimize noise and improve efficiency.