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AOZ1210 Datasheet(PDF) 7 Page - Alpha & Omega Semiconductors |
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AOZ1210 Datasheet(HTML) 7 Page - Alpha & Omega Semiconductors |
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7 / 14 page  AOZ1210 Rev. 1.3 December 2007 www.aosmd.com Page 7 of 14 Detailed Description The AOZ1210 is a current-mode step down regulator with integrated high side NMOS switch. It operates from a 4.5V to 27V input voltage range and supplies up to 2A of load current. The duty cycle can be adjusted from 6% to 85% allowing a wide range of output voltages. Features include; enable control, Power-On Reset, input under voltage lockout, fixed internal soft-start and thermal shut down. The AOZ1210 is available in SO-8 package. Enable and Soft Start The AOZ1210 has an internal soft start feature to limit in-rush current and ensure the output voltage ramps up smoothly to the regulation voltage. A soft start process begins when the input voltage rises to 4.1V and voltage on EN pin is HIGH. In the soft start process, the output voltage is typically ramped to regulation voltage in 4 ms. The 4.0 ms soft start time is set internally. If the enable function is not used, connect the EN pin to VIN. Pulling EN to ground will disable the AOZ1210. Do not leave EN open. The voltage on the EN pin must be above 2.5 V to enable the AOZ1210. When voltage on EN pin falls below 0.6V, the AOZ1210 is disabled. If an application circuit requires the AOZ1210 to be disabled, an open drain or open collector circuit should be used to interface with the EN pin. Steady-State Operation Under steady-state conditions, the converter operates in fixed frequency and Continuous-Conduction Mode (CCM). The AOZ1210 integrates an internal N-MOSFET as the high-side switch. Inductor current is sensed by amplifying the voltage drop across the drain to source of the high side power MOSFET. Since the N-MOSFET requires a gate voltage higher than the input voltage, a boost capacitor connected between the LX and BST pins drives the gate. The boost capacitor is charged while LX is low. An internal 10 Ω switch from LX to GND is used to ensure that LX is pulled to GND even in the light load. Output voltage is divided down by the external voltage divider at the FB pin. The difference of the FB pin voltage and reference is amplified by the internal transconductance error amplifier. The error voltage, which shows on the COMP pin, is compared against the current signal. The current signal is the sum of inductor current signal and ramp compensation signal, at the 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 freewheel- ing through the Schottky diode to the output. Switching Frequency The AOZ1210 switching frequency is fixed and set by an internal oscillator. The switching frequency is set to 370kHz. Output Voltage Programming Output voltage can be set by feeding back the output to the FB pin with a resistor divider network. In the applica- tion circuit shown in Figure 1. The resistor divider network includes R1 and R2. Typically, a design is started by picking a fixed R2 value and calculating the required R1 value with equation below. Some standard values for R1 and R2 for the most commonly used output voltages are listed in Table 1. Table 1. The combination of R1 and R2 should be large enough to avoid drawing excessive current from the output, which will cause power loss. Protection Features The AOZ1210 has multiple protection features to prevent system circuit damage under abnormal conditions. Over Current Protection (OCP) The sensed inductor current signal is also used for over current protection. Since the AOZ1210 employs peak current mode control, the COMP pin voltage is propor- tional to the peak inductor current. The COMP pin voltage is limited to be between 0.4V and 2.5V internally. The peak inductor current is automatically limited cycle by cycle. VO (V) R1 (kΩ) R2 (kΩ) 0.8 1.0 Open 1.2 4.99 10 1.5 10 11.5 1.8 12.7 10.2 2.5 21.5 10 3.3 31.6 10 5.0 52.3 10 V O 0.8 1 R 1 R 2 ------- + × = |
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Similar Description - AOZ1210 |
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