MAXIM公司的MAX15015是一款降壓DC-DC變換器和一個50mA、低靜態電流低壓差(LDO)穩壓器。LDO穩壓器非常適合為汽車應用中的不關斷電路供電。MAX15015的DC-DC變換器輸入電壓范圍為4.5V至40V。DC-DC變換器的輸出電壓可調范圍為1.26V至32V，可提供最大1A負載電流。這些器件采用前饋電壓模式控制方案，在高壓開關環境中可以提供良好的抗噪聲性能，還提供外部補償允許在較寬的范圍內靈活選擇電感值和電容類型。按照選用的器件型號，開關頻率在內部固定為135kHz和500kHz。此外，通過SYNC輸入，開關頻率還可與外部時鐘信號同步。通過自動切換到脈沖模式，可以提高輕載效率。軟啟動時間可由外部電容調整。DC-DC轉換器可獨立于LDO被禁止，從而把靜態電流降低到47µA (典型值)。此外，輸出電壓還可通過外部電阻分壓器從1.5V至11V進行調整。LDO部分還具有可調整延時周期的/RESET輸出。保護功能包括逐周期限流、打嗝式短路保護和過熱關斷。本文首先介紹芯片的簡介、特性、內部框圖及應用領域，并給出相應設計方案的設計原理圖、元器件列表及PCB元件布局圖。
The MAX15014–MAX15017 combine a step-down DCDC converter and a 50mA, low-quiescent-current low-dropout (LDO) regulator. The LDO regulator is ideal for powering always-on circuitry in automotive applications. The DC-DC converter input voltage range is 4.5V to 40V for the MAX15015/MAX15016, and 7.5V to 40V for the MAX15014/MAX15017.
The DC-DC converter output is adjustable from 1.26V to 32V and can deliver up to 1A of load current. These devices utilize a feed-forward voltage-mode control scheme for good noise immunity in the high-voltage switching environment and offer external compensation allowing for maximum flexibility with a wide selection of inductor values and capacitor types. The switching frequency is internally fixed at 135kHz and 500kHz, depending on the version chosen. Moreover, the switching frequency can be synchronized to an external clock signal through the SYNC input. Light load efficiency is improved by automatically switching to a pulse-skip mode. The soft-start time is adjustable with an external capacitor. The DC-DC converter can be disabled independent of the LDO, thus reducing the quiescent current to 47µA (typ).
The LDO linear regulators operate from 5V to 40V and deliver a guaranteed 50mA load current. The devices feature a preset output voltage of 5V (MAX1501_A) or 3.3V (MAX1501_B). Alternatively, the output voltage can be adjusted from 1.5V to 11V by using an external resistive divider. The LDO section also features an active-low RESET output with adjustable timeout period. Protection features include cycle-by-cycle current limit, hiccup-mode output short-circuit protection, and thermal shutdown. All devices are available in a space-saving, high-power (2.86W), 36-pin TQFN package and are rated for operation over the -40°C to +125°C automotive temperature range.
MAX15015主要特性：
Combined DC-DC Converters and Low-Quiescent-Current LDO Regulators
1A DC-DC Converters Operate from 4.5V to 40V (MAX15015/MAX15016) or 7.5V to 40V (MAX15014/MAX15017)
Switching Frequency of 135kHz (MAX15014/MAX15016) or 500kHz (MAX15015/MAX15017)
50mA LDO Regulator Operates from 5V to 40V Independent of the DC-DC Converter
47µA Quiescent Current with DC-DC Converter Off and LDO On
6µA System Shutdown Current
Frequency Synchronization Input
Shutdown/Enable Inputs
Adjustable Soft-Start Time
Open-Drain Active-Low RESET Output with Programmable Timeout Delay
Thermal Shutdown and Output Short-Circuit Protection
Space-Saving (6mm x 6mm) Thermally Enhanced 36-Pin TQFN Package
MAX15015應用：
Automotive Body Control Modules
Automotive Instrument Cluster
Car Radios
Navigation Systems
圖1. MAX15015內部方框圖
MAX15015方案介紹：
The MAX15015A evaluation kit (EV kit) is a fully assembled and tested PCB that evaluates the MAX15015A PWM/PFM step-down converter, which integrates a high-side switch and an LDO regulator. The MAX15015A EV kit operates over a wide input-voltage range of 4.5V to 40V and provides up to 1A at the 3.3V output. The LDO regulator provides up to 50mA at the preset 5V output. The MAX15015A features undervoltage lockout, overcurrent, and thermal-shutdown protection.
The MAX15015A normally operates as a PWM converter and automatically switches to PFM mode at light loads to improve efficiency. The MAX15015A switching frequency is preset to 500kHz and features a SYNC input to provide external frequency synchronization for sensitive applications. The EV kit provides PCB pads to evaluate the SYNC and ENABLE features of the MAX15015A. The EV kit board can also be used to evaluate the MAX15015B. The MAX15015A can operate over the automotive temperature range of -40°C to +125°C.
Key Features
3.3V, 1A, 500kHz Step-Down Converter
5V, 50mA LDO Regulator
LDO Voltage Adjustable Up to 11V
Independent Turn On/Off Control for Step-Down Converter (EN_SW)
Regulator Power-On Reset with Adjustable Timeout Period
84% High Efficiency at VIN = 12V and IOUT = 1A
Automatic PWM/PFM Mode
Overcurrent and Thermal-Shutdown Protection
Fully Assembled and Tested
MAX15015方案原理圖：
圖2. MAX15015方案原理圖
MAX15015方案材料清單：
PCB元件布局圖：
