Datasheet AOZ6683CI (Alpha & Omega) - 9

AOZ6683CI Detailed Description
Comparing with regulators using freewheeling Schottky diode, AOZ6683CI uses freewheeling MOSFET to AOZ6683CI is a current-mode step down regulator with realize synchronous rectification. This greatly improves integrated high-side and low-side power switches. It the converter efficiency and reduces power loss in the operates from 4.5V to 18V input voltage range and low-side switch. supplies up to 3A of continuous load current. Functional features such as Enable control, Power-On Reset (POR), AOZ6683CI uses a N-channel MOSFET as the high-side input Under-Voltage LockOut (UVLO), output Over- switch. Since the MOSFET requires a gate voltage Voltage Protection (OVP), internal soft-start, and Over- higher than the input voltage to turn it on, a boost Temperature protection (OTP) shut down are built in. capacitor is needed between BST (Pin 6) and LX (Pin 2) AOZ6683CI is available in compact TSOT23-6L to drive the MOSFET gate. The boost capacitor charge is package. being replenished when LX is low.
Enable and Soft Start Output Voltage Programming
AOZ6683CI has internal soft start to limit the in-rush Output voltage can be set by feeding back the output to current and ensure the output voltage ramps up smoothly the FB pin through a resistor divider network as shown in to regulation voltage during start up. A soft start process Figure 1. The T-type resistor divider network includes R begins when the input voltage VIN rises to 4.1V and 1 R enable voltage EN is higher than 2V. The soft start time is 2 and RT. Design starts by selecting a fixed R2 value and then calculates the required R pre-programmed to 2.8ms typical. 1 using the equation below. RT can be used to adjust the feedback loop gain with internal compensation. The EN pin of the AOZ6683CI is active high. Do not leave it open or connect to VIN if enable control signal is  R  not available. The voltage on EN pin must be above 2V to V 1 =   + --- OUT 0.8 1  enable and below 0.6V to disable AOZ6683CI. R  2
Light Load and PWM Operation
Some standard value of R1, R2 and most used output Under low output current condition, AOZ6683CI will voltage values are listed in Table 1. operate in pulse energy mode to achieve high efficiency. In pulse energy mode, the PWM will not turn off until the
VO (V) R1 (k
Ω)
R2 (k
Ω) on time get a fixed time which is defined by Input Voltage (VIN), Output Voltage (Vout), and Switching Frequency. 0.8 1.0 open 1.2 5.0 10
Steady-State Operation
1.5 10.0 11.5 Under normal to heavy load steady-state condition, 1.8 12.7 10.2 AOZ6683CI operates in fixed frequency and Continuous- 2.5 21.5 10 Conduction Mode (PWM). 3.3 31.1 10 AOZ6683CI integrates internal high-side and low-side 5.0 52.3 10 power MOSFET. Inductor current is sensed through the current being conducted by the power MOSFET. Output
Table 1. Typical Resistor Divider Values for FB Input
voltage is determined by the external voltage divider between Vout, FB, and GND. The difference of the FB Combination of R1 and R2 should be large enough to voltage and internal reference is amplified by the avoid drawing excessive current from the output, which transconductance error amplifier. The error voltage is will cause power loss. compared against the current signal (sum of inductor current signal and input and output modulated voltage ramp compensation signal) at PWM comparator stage. If the current signal is less than the error voltage, the internal high-side switch is on. The inductor current flows from the input through the inductor to the output. When the current signal exceeds the error voltage, the high- side switch is off. The inductor current is freewheeling through the internal low-side switch to output. The internal adaptive MOSFET driver guarantees no turn on overlap between high-side and low-side switch. Rev. 2.0 January 2019
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