Datasheet AOZ6682CI (Alpha & Omega) - 9

AOZ6682CI Protection Features
The relation between the input capacitor RMS current and voltage conversion ratio is calculated and shown in AOZ6682CI has multiple protection features to prevent Figure 11 below. It can be seen that when V system circuit damage under abnormal conditions. OUT is half of VIN, CIN is under the worst current stress. The worst cur-
Over Current Protection (OCP)
rent stress on CIN is 0.5·IOUT. The cycle by cycle current limit is applied for over current 0.5 protection. 0.4
Power-On Reset (POR)
A power-on reset circuit monitors the VIN voltage. When 0.3 I (m) CIN_RMS VIN voltage exceeds 4.1V, the converter will start to IO operate. When VIN voltage falls below 3.7V, the 0.2 converter will be shut down. 0.1
Thermal Protection
0 An internal temperature sensor monitors the junction 0 0.5 1 temperature. It shuts down the internal control circuit and m high side switch if the junction temperature exceeds
Figure 2. I
150ºC. The regulator will restart automatically under the
CIN vs. Voltage Conversion Ratio
control of soft-start circuit when the junction temperature For reliable operation and best performance, the input decreases to 100ºC. capacitors must have current rating higher than ICIN-RMS at worst operating conditions. Ceramic capacitors are
Application Information
preferred for input capacitors because of their low ESR The basic AOZ6682CI application circuit is show in and high current rating. Depending on the application Figure 1. Component selection is explained below. circuits, other low ESR tantalum capacitor may also be used. When selecting ceramic capacitors, X5R or X7R
Input Capacitor
type dielectric ceramic capacitors should be used for The input capacitor must be connected to the VIN (Pin 3) their better temperature and voltage characteristics. Note and GND (Pin 1) of AOZ6682CI to maintain steady input that the ripple current rating from capacitor manufactures voltage and filter out the pulsing input current. The are based on certain amount of life time. Further de- voltage rating of input capacitor must be greater than rating may be necessary in practical design. maximum input voltage plus ripple voltage.
Inductor
The input ripple voltage can be approximated by The inductor is used to supply constant current to output equation below: when it is driven by a switching voltage. For given input and output voltage, inductance and switching frequency IOUT  VOUT VOUT together decide the inductor ripple current as below: V = ---------   – -------  ------- IN 1  f  C  V IN IN  VIN V  V  I OUT = ------- OUT   – ------- L 1  f  L V  IN  Since the input current is discontinuous in a buck converter, the current stress on the input capacitor is another concern when selecting the capacitor. For a buck The peak inductor current is: circuit, the RMS value of input capacitor current can be I calculated by: I L = + ---- Lpeak IOUT 2 OUT V V I  I  1 ( OUT  ) High inductance gives low inductor ripple current but CIN _ RMS OUT VIN VIN requires larger size inductor to avoid saturation. Low ripple current reduces inductor core losses. It also reduces RMS current through inductor and switches, if let m equal the conversion ratio: which results in less conduction loss. Usually, peak to V peak ripple current on inductor is designed to be 20% to O ---- = m 40% of output current. VIN Rev. 1.0 December 2018
www.aosmd.com
Page 9 of 14