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AOZ1282CI — 1.2 A Simple Buck Regulator

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by Kyle Bergstedt

Alpha & Omega Semiconductor AOZ1282CI EZBuck. 4.5–36 V input, 1.2 A output adjustable down to 0.8 V, 450 kHz PWM, internal 420 mΩ NMOS, SOT23-6L.

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Source: Alpha & Omega AOZ1282CI Datasheet
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 RDS(on) 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 (VIN) 40 V
LX to GND −0.7 to VIN+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 VLX + 6 V
Junction Temperature (TJ) +150 °C
Storage Temperature (TS) −65 to +150 °C
ESD Rating (HBM, 1.5 kΩ + 100 pF) 2 kV

Recommended Operating Conditions

Parameter Rating
Supply Voltage (VIN) 4.5 V to 36 V
Output Voltage (VOUT) 0.8 V to 0.85×VIN
Ambient Temperature (TA) −40 °C to +85 °C
Package Thermal Resistance (θJA) 220 °C/W (SOT23-6L)

Electrical Characteristics

TA = 25 °C, VIN = 12 V, unless otherwise specified. Bold indicates temperature range of −40 °C to +85 °C.

Parameter Symbol Conditions Min Typ Max Units
Supply Voltage VIN 4.5 36 V
Input Under-Voltage Lockout Threshold VUVLO VIN rising / falling 2.3 2.9 V
UVLO Hysteresis VUVLO_HYS 260 mV
Quiescent Supply Current IIN IOUT = 0, FB = 1 V, EN > 1.2 V 1 1.5 mA
Shutdown Supply Current IOFF EN = 0 V 8 µA
Feedback Voltage VFB 784 800 816 mV
Load Regulation VFB_LOAD 0.12 A < Load < 1.08 A 0.5 %
Line Regulation VFB_LINE Load = 600 mA 0.03 %/V
FB Input Current IFB FB = Regulation 500 nA
EN Input Threshold (Off) VEN_OFF Off threshold 0.4 V
EN Input Threshold (On) VEN_ON On threshold 1.2 V
EN Input Hysteresis VEN_HYS 200 mV
EN Input Current IEN 3 µA
Switching Frequency fO 360 450 540 kHz
Maximum Duty Cycle DMAX 87 %
Minimum On Time tON_MIN 150 ns
Current Limit ILIM 1.5 1.9 A
Thermal Shutdown Limit (TJ rising) TSD 150 °C
Thermal Shutdown Limit (TJ falling) 110 °C
Soft-Start Interval tSS 1.5 ms
NMOS Leakage ILEAKAGE EN = 0, LX = 0 10 µA
NMOS On-Resistance RDS(on) 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 C2, bootstrap capacitor C3, and feedback resistors R1/R2. 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→COUT→Schottky — should both be kept tight to minimize noise and improve efficiency.