Datenblatt-Suchmaschine für elektronische Bauteile |
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LD1985-2J-AF5-R Datenblatt(PDF) 7 Page - Unisonic Technologies |
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LD1985-2J-AF5-R Datenblatt(HTML) 7 Page - Unisonic Technologies |
7 / 10 page LD1985 LINEAR INTEGRATED CIRCUIT UNISONICTECHNOLOGIESCO.,LTD 7 of 10 www.unisonic.com.tw QW-R102-021,C APPLICATION INFORMATION EXTERNAL CAPACITORS An external capacitor for regulator stability is required. This capacitor must be selected to meet the requirements of minimum capacitance and equivalent series resistance. It is recommended to solder input and output capacitors as close as possible to the relative pins. INPUT CAPACITOR A 1µF input capacitor (ceramic, tantalum or film capacitors can be used) is required with the UTC LD1985 (amount of capacitance can be increased without limit). This capacitor must be located a distance less than 0.5" from the input pin of the device and returned to a clean analog ground. OUTPUT CAPACITOR The output capacitor must meet both the requirement for minimum amount of capacitance and E.S.R. (equivalent series resistance) value. The output capacitor must maintain its ESR in the stable region over the full operating temperature to assure stability. Also, capacitor tolerance and variation with temperature must be considered to assure the minimum amount of capacitance is provided over time. Due to the different loop gain and the stability improves for higher output versions, if low E.S.R. ceramic type is used, the recommended minimum output capacitor value are is 1µF for output voltages equal or major than 3.8V, 2.2µF for VOUT going from 1.8~3.3V, and 3.3µF for the other versions. However, if an output capacitor lower than the suggestion, it's possible to make stable the regulator adding a resistor in series to the capacitor. This capacitor should be located not more than 0.5" from the output pin of the device and returned to a clean analog ground. INHIBIT INPUT OPERATION The inhibit pin can be used to turn OFF the regulator when pulled low, so drastically reducing the current consumption down to less than 1µA. When the inhibit feature is not used, this pin must be tied to VIN to keep the regulator output ON over time. To assure proper operation, the signal source used to drive the inhibit pin must be able to swing above and below the specified thresholds listed in the electrical characteristics section under VIH, VIL. Any slew rate can be used to drive the inhibit. REVERSE CURRENT The power transistor used in the UTC LD1985 has not an inherent diode connected between the regulator input and output. If the output is forced above the input, no current will flow from the output to the input across the series pass transistor. When a VREV voltage is applied on the output, the reverse current measured flows to the GND across the two feedback resistors. This current typical value is 160µA. R1 and R2 resistors are implanted type; and typical values are respectively 42.6 KΩ and 51.15 KΩ. 2 VREV Bypass IN 1μF + VIN INH VINH 1 GND R2 R1 OUT 4.7μF + A VIN Fig 1. REVERSE CURRENT TEST CIRCUIT |
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