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AP2142A Datasheet(PDF) 11 Page - Diodes Incorporated |
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AP2142A Datasheet(HTML) 11 Page - Diodes Incorporated |
11 / 17 page AP2142A/AP2152A 0.5A DUAL CHANNEL CURRENT-LIMITED POWER SWITCH WITH OUTPUT DISCHARGE AP2142A/2152A Document number: DS32191 Rev. 2 - 2 11 of 17 www.diodes.com October 2010 © Diodes Incorporated Application Note Power Supply Considerations A 0.1 μF to 1μF X7R or X5R ceramic bypass capacitor between IN and GND, close to the device, is recommended. Placing a high-value electrolytic capacitor on the input and output pin(s) is recommended when the output load is heavy. This precaution reduces power-supply transients that may cause ringing on the input. Additionally, bypassing the output with a 1 μF ceramic capacitor improves the immunity of the device to short- circuit transients. Over-current and Short Circuit Protection An internal sensing FET is employed to check for over-current conditions. Unlike current-sense resistors, sense FETs do not increase the series resistance of the current path. When an overcurrent condition is detected, the device maintains a constant output current and reduces the output voltage accordingly. Complete shutdown occurs only if the fault stays long enough to activate thermal limiting. Three possible overload conditions can occur. In the first condition, the output has been shorted to GND before the device is enabled or before VIN has been applied. The AP2142A/AP2152A senses the short circuit and immediately clamps output current to a certain safe level namely ILIMIT. In the second condition, an output short or an overload occurs while the device is enabled. At the instance the overload occurs, higher inrush current may flow for a very short period of time before the current limit function can react. The input capacitor(s) rapidly discharge through the device, activating current limit circuitry. Protection is achieved by momentarily opening the P-MOS high-side power switch and then gradually turning it on. After the current limit function has tripped (reached the over-current trip threshold), the device switches into current limiting mode and the current is clamped at ILIMIT. The threshold for activating current limiting is 0.7A typical per channel. In the third condition, the load has been gradually increased beyond the recommended operating current. The current is permitted to rise until the current-limit threshold (ITRIG) is reached or until the thermal limit of the device is exceeded. The AP2142A/AP2152A is capable of delivering current up to the current-limit threshold without damaging the device. Once the threshold has been reached, the device switches into its current limiting mode and is set at ILIMIT. FLG Response When an over-current or over-temperature shutdown condition is encountered, the FLG open-drain output goes active low after a nominal 7-ms deglitch timeout. The FLG output remains low until both over-current and over- temperature conditions are removed. Connecting a heavy capacitive load to the output of the device can cause a momentary over-current condition, which does not trigger the FLG due to the 7-ms deglitch timeout. The AP2142A/AP2152A is designed to eliminate false over-current reporting without the need of external components to remove unwanted pulses. Power Dissipation and Junction Temperature The low on-resistance of the internal MOSFET allows the small surface-mount packages to pass large current. Using the maximum operating ambient temperature (TA) and RDS(ON), the power dissipation can be calculated by: PD = RDS(ON)× I 2 Finally, calculate the junction temperature: TJ = PD x RθJA + TA Where: TA= Ambient temperature °C RθJA = Thermal resistance PD = Total power dissipation |
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