Datasheet AOZ6763DI (Alpha & Omega) - 8
| Manufacturer | Alpha & Omega |
| Description | 3A 1.25MHz Synchronous EZBuck Regulator |
| Pages / Page | 15 / 8 — AOZ6763DI. Detailed Description. Enable and Soft Start. Output Voltage … |
| File Format / Size | PDF / 889 Kb |
| Document Language | English |
AOZ6763DI. Detailed Description. Enable and Soft Start. Output Voltage Programming. Light Load and PWM Operation
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AOZ6763DI Detailed Description
switch to output. The internal adaptive FET driver guarantees no turn on overlap of both high-side and low- The AOZ6763DI is a current-mode step down regulator side switch. with integrated high-side NMOS switch and low-side NMOS switch. It operates from a 4.5V to 18V input Comparing with regulators using freewheeling Schottky voltage range and supplies up to 3A of load current. diodes, the AOZ6763DI uses freewheeling NMOSFET to Features include, enable control, Power-On Reset, input realize synchronous rectification. It greatly improves the under voltage lockout, output over voltage protection, converter efficiency and reduces power loss in the low- internal soft-start and thermal shut down. side switch. The AOZ6763DI is available in DFN3x3 package. The AOZ6763DI uses a N-Channel MOSFET as the high-side switch. Since the NMOSFET requires a gate
Enable and Soft Start
voltage higher than the input voltage, a boost capacitor is The AOZ6763DI has internal soft start feature to limit in- needed between LX pin and BST pin to drive the gate. rush current and ensure the output voltage ramps up The boost capacitor is charged while LX is low smoothly to regulation voltage. A soft start process begins when the input voltage rises to 4.1V and voltage
Output Voltage Programming
on EN pin is HIGH. The soft start time is programmed by Output voltage can be set by feeding back the output to internal soft start capacitor and is set to 3.5ms (Typ). the FB pin by using a resistor divider network. In the application circuit shown in Figure 1. Usually, a design is The EN pin of the AOZ6763DI is active high. Connect the started by picking a fixed R EN pin to VIN if enable function is not used. Pull it to 2 value and calculating the required R1 with equation below. ground will disable the AOZ6763DI. Do not leave it open. The voltage on EN pin must be above 2V to enable the R AOZ6763DI. When voltage on EN pin falls below 0.6V, V 1 = + --- O 0.6 1 the AOZ6763DI is disabled. R 2
Light Load and PWM Operation
Combination of R1 and R2 should be large enough to Under low output current settings, the AOZ6763DI will avoid drawing excessive current from the output, which operate with pulse energy mode to obtain high efficiency. will cause power loss. In pulse energy mode, the PWM will not turn off until the on time get a fixed time which is defined by Vin, Vo and Some standard value of R1, R2 and most used output switching frequency. voltage values are listed in Table 1.
Steady-State Operation VO (V) R1 (k
Ω)
R2 (k
Ω) Under heavy load steady-state conditions, the converter 1.0 10 15 operates in fixed frequency and Continuous-Conduction 1.2 10 10 Mode (CCM). 1.5 15 10 he AOZ6763DI integrates an internal N-MOSFET as the 1.8 20 10 high-side switch. Inductor current is sensed by amplifying 2.5 31.6 10 the voltage drop across the drain to source of the high side power MOSFET. Output voltage is divided down by 3.3 68.1 15 the external voltage divider at the FB pin. The difference 5.0 110 15 of the FB pin voltage and reference is amplified by the internal transconductance error amplifier. The error
Table 1.
voltage is compared against the current signal, which is sum of inductor current signal and input and output modulated voltage ramp compensation signal, at PWM comparator input. 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 N-MOSFET Rev. 1.0 October 2019
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Page 8 of 15
switch to output. The internal adaptive FET driver guarantees no turn on overlap of both high-side and low- The AOZ6763DI is a current-mode step down regulator side switch. with integrated high-side NMOS switch and low-side NMOS switch. It operates from a 4.5V to 18V input Comparing with regulators using freewheeling Schottky voltage range and supplies up to 3A of load current. diodes, the AOZ6763DI uses freewheeling NMOSFET to Features include, enable control, Power-On Reset, input realize synchronous rectification. It greatly improves the under voltage lockout, output over voltage protection, converter efficiency and reduces power loss in the low- internal soft-start and thermal shut down. side switch. The AOZ6763DI is available in DFN3x3 package. The AOZ6763DI uses a N-Channel MOSFET as the high-side switch. Since the NMOSFET requires a gate
Enable and Soft Start
voltage higher than the input voltage, a boost capacitor is The AOZ6763DI has internal soft start feature to limit in- needed between LX pin and BST pin to drive the gate. rush current and ensure the output voltage ramps up The boost capacitor is charged while LX is low smoothly to regulation voltage. A soft start process begins when the input voltage rises to 4.1V and voltage
Output Voltage Programming
on EN pin is HIGH. The soft start time is programmed by Output voltage can be set by feeding back the output to internal soft start capacitor and is set to 3.5ms (Typ). the FB pin by using a resistor divider network. In the application circuit shown in Figure 1. Usually, a design is The EN pin of the AOZ6763DI is active high. Connect the started by picking a fixed R EN pin to VIN if enable function is not used. Pull it to 2 value and calculating the required R1 with equation below. ground will disable the AOZ6763DI. Do not leave it open. The voltage on EN pin must be above 2V to enable the R AOZ6763DI. When voltage on EN pin falls below 0.6V, V 1 = + --- O 0.6 1 the AOZ6763DI is disabled. R 2
Light Load and PWM Operation
Combination of R1 and R2 should be large enough to Under low output current settings, the AOZ6763DI will avoid drawing excessive current from the output, which operate with pulse energy mode to obtain high efficiency. will cause power loss. In pulse energy mode, the PWM will not turn off until the on time get a fixed time which is defined by Vin, Vo and Some standard value of R1, R2 and most used output switching frequency. voltage values are listed in Table 1.
Steady-State Operation VO (V) R1 (k
Ω)
R2 (k
Ω) Under heavy load steady-state conditions, the converter 1.0 10 15 operates in fixed frequency and Continuous-Conduction 1.2 10 10 Mode (CCM). 1.5 15 10 he AOZ6763DI integrates an internal N-MOSFET as the 1.8 20 10 high-side switch. Inductor current is sensed by amplifying 2.5 31.6 10 the voltage drop across the drain to source of the high side power MOSFET. Output voltage is divided down by 3.3 68.1 15 the external voltage divider at the FB pin. The difference 5.0 110 15 of the FB pin voltage and reference is amplified by the internal transconductance error amplifier. The error
Table 1.
voltage is compared against the current signal, which is sum of inductor current signal and input and output modulated voltage ramp compensation signal, at PWM comparator input. 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 N-MOSFET Rev. 1.0 October 2019
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Page 8 of 15
