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RT9018B1KPSP Datasheet(PDF) 9 Page - Richtek Technology Corporation |
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RT9018B1KPSP Datasheet(HTML) 9 Page - Richtek Technology Corporation |
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9 / 12 page  RT9018A/B 9 DS9018A/B-04 September 2007 www.richtek.com Application Information Adjustable Mode Operation The output voltage of RT9018A/B is adjustable from 0.8V to VIN by external voltage divider resisters as shown in Typical Application Circuit (Figure 2). The value of resisters R1 and R2 should be more than 10k Ω to reduce the power loss. Enable The RT9018A/B goes into shutdown mode when the EN pin is in the logic low condition. During this condition, the pass transistor, error amplifier, and band gap are turned off, reducing the supply current to 10uA typical. The RT9018A/B goes into operation mode when the EN pin is in the logic high condition. If the EN pin is floating, NOTE that the RT9018A/B internal initial logic level. For RT9018A, the EN pin function pulls high level internally. So the regulator will be turn on when EN pin is floating. For RT9018B, the EN pin function pulls low level internally. So the regulator will be turn off when EN pin is floating. Output Capacitor The RT9018A/B is specifically designed to employ ceramic output capacitors as low as 10uF. The ceramic capacitors offer significant cost and space savings, along with high frequency noise filtering. Input Capacitor Good bypassing is recommended from input to ground to help improve AC performance. A 10uF input capacitor or greater located as close as possible to the IC is recommended. Current Limit The RT9018A/B contains an independent current limit and the short circuit current protection to prevent unexpected applications. The current limit monitors and controls the pass transistor ’ s gate voltage, limiting the output current to higher than 4.5A typical. When the output voltage is less than 0.4V, the short circuit current protection starts the current fold back function and maintains the loading current 1.8A. The output can be shorted to ground indefinitely without damaging the part. Power Good The power good function is an open-drain output. Connects 100k Ω pull up resistor to VOUT to obtain an output voltage. The PGOOD pin will output high immediately after the output voltage arrives 90% of normal output voltage. The PGOOD pin will output high with typical 1.5ms delay time. Thermal-Shutdown Protection Thermal protection limits power dissipation to prevent IC over temperature in RT9018A/B. When the operation junction temperature exceeds 160 °C, the over-temperature protection circuit starts the thermal shutdown function and turns the pass transistor off. The pass transistor turn on again after the junction temperature cools by 30 °C. RT9018A/B lowers its OTP trip level from 160 °C to 110°C when output short circuit occurs (VOUT < 0.4V). It limits IC case temperature under 100 °C and provides maximum safety to customer while output short circuit occurring. Power Dissipation For continuous operation, do not exceed absolute maximum operation junction temperature 125 °C. The power dissipation definition in device is: PD = (VIN − VOUT) x IOUT + VIN x IQ The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junctions to ambient. The maximum power dissipation can be calculated by following formula: PD(MAX) = ( TJ(MAX) − TA ) / θJA Where TJ(MAX) is the maximum operation junction temperature 125 °C, TAis the ambient temperature and the θJA is the junction to ambient thermal resistance. For recommended operating conditions specification of RT9018A/B, where TJ (MAX) is the maximum junction temperature of the die (125 °C) and TA is the maximum ambient temperature. The junction to ambient thermal resistance for SOP-8 (Exposed Pad) package is 75 °C/W on the standard JEDEC 51-7 (4 layers, 2S2P) thermal test board. The copper thickness is 2oz. The maximum power dissipation at TA = 25 °C can be calculated by following formula: |
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