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AOZ1036 Datasheet(PDF) 8 Page - Alpha & Omega Semiconductors |
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AOZ1036 Datasheet(HTML) 8 Page - Alpha & Omega Semiconductors |
8 / 17 page AOZ1036 Rev. 1.1 September 2010 www.aosmd.com Page 8 of 17 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 AOZ1036 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 AOZ1036 employs peak current mode control, the COMP pin voltage is proportional 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. When the output is shorted to ground under fault conditions, the inductor current decays very slow during a switching cycle because of VO = 0V. To prevent catastrophic failure, a secondary current limit is designed inside the AOZ1036. The measured inductor current is compared against a preset voltage which represents the current limit, between 3.5A and 5.0A. When the output current is more than current limit, the high side switch will be turned off. The converter will initiate a soft start once the over-current condition disappears. Power-On Reset (POR) A power-on reset circuit monitors the input voltage. When the input voltage exceeds 4.1V, the converter starts operation. When input voltage falls below 3.7V, the converter will be shut down. Thermal Protection An internal temperature sensor monitors the junction temperature. It shuts down the internal control circuit and high side PMOS if the junction temperature exceeds 150ºC. The regulator will restart automatically under the control of soft-start circuit when the junction temperature decreases to 100ºC. Application Information The basic AOZ1036 application circuit is show in Figure 1. Component selection is explained below. Input Capacitor The input capacitor must be connected to the VIN pin and PGND pin of AOZ1036 to maintain steady input voltage and filter out the pulsing input current. The voltage rating of input capacitor must be greater than maximum input voltage plus ripple voltage. The input ripple voltage can be approximated by the equation below: Since the input current is discontinuous in a buck con- verter, the current stress on the input capacitor is another concern when selecting the capacitor. For a buck circuit, the RMS value of input capacitor current can be calculated by: if we let m equal the conversion ratio: The relation between the input capacitor RMS current and voltage conversion ratio is calculated and shown in Figure 2 on the next page. It can be seen that when VO is half of VIN, CIN is under the worst current stress. The worst current stress on CIN is 0.5 x IO. Vo (V) R1 (k Ω) R2 (k Ω) 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 31.1 10 5.0 52.3 10 ΔV IN I O fC IN × ----------------- 1 V O V IN --------- – ⎝⎠ ⎜⎟ ⎛⎞ V O V IN --------- × × = I CIN_RMS I O V O V IN --------- 1 V O V IN --------- – ⎝⎠ ⎜⎟ ⎛⎞ × = V O V IN --------- m = |
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