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Zakładka z wyszukiwarką danych komponentów |
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Zakładka z wyszukiwarką danych komponentów |
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ACT8847_17 Arkusz danych(PDF) 35 Page - Active-Semi, Inc |
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ACT8847_17 Arkusz danych(HTML) 35 Page - Active-Semi, Inc |
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35 / 42 page  ACT8847 Rev 9, 27-June-17 Innovative PowerTM - 35 - www.active-semi.com Copyright © 2015-2017 Active-Semi, Inc. ActivePMUTM is a trademark of Active-Semi. I2CTM is a trademark of NXP. LOW-NOISE, LOW-DROPOUT LINEAR REGULATORS General Description ACT8847 features eight low-noise, low-dropout linear regulators (LDOs) that supply up to 350mA. Three of these LDOs (REG10, REG11, and REG12) supports extended input voltage range down to 1.7V. Each LDO has been optimized to achieve low noise and high-PSRR. Output Current Limit Each LDO contains current-limit circuitry featuring a current-limit fold-back function. During normal and moderate overload conditions, the regulators can support more than their rated output currents. During extreme overload conditions, however, the current limit is reduced by approximately 30%, reducing power dissipation within the IC. Compensation The LDOs are internally compensated and require very little design effort, simply select input and output capacitors according to the guidelines below. Input Capacitor Selection Each LDO requires a small ceramic input capacitor to supply current to support fast transients at the input of the LDO. Bypassing each INL pin to GA with 1μF. High quality ceramic capacitors such as X7R and X5R dielectric types are strongly recommended. Output Capacitor Selection Each LDO requires a small 2.2μF ceramic output capacitor for stability . For best performance, each output capacitor should be connected directly between the output and GA pins, as close to the output as possible, and with a short, direct connection. High quality ceramic capacitors such as X7R and X5R dielectric types are strongly recommended. Configuration Options Output Voltage Programming By default, each LDO powers up and regulates to its default output voltage. Once the system is enabled, each output voltage may be independently programmed to a different value by writing to the regulator's VSET[-] register via the I2C serial interface as shown in Table 5. Enable / Disable Control During normal operation, each LDO may be enabled or disabled via the I2C interface by writing to that LDO's ON[ ] bit. Output Discharge Each of the LDOs features an optional output discharge function, which discharges the output to ground through a 1.5kΩ resistance when the LDO is disabled. This feature may be enabled or disabled by setting DIS[-]; set DIS[-] to 1 to enable this function, clear DIS[-] to 0 to disable it. OK[ ] and Output Fault Interrupt Each LDO features a power-OK status bit that can be read by the system microprocessor via the interface. If an output voltage is lower than the power-OK threshold, typically 11% below the programmed regulation voltage, the value of that regulator's OK[-] bit will be 0. If a LDO's nFLTMSK[-] bit is set to 1, the ACT8847 will interrupt the processor if that LDO's output voltage falls below the power-OK threshold. In this case, nIRQ will assert low and remain asserted until either the regulator is turned off or back in regulation, and the OK[-] bit has been read via I2C. PCB Layout Considerations The ACT8847’s LDOs provide good DC, AC, and noise performance over a wide range of operating conditions, and are relatively insensitive to layout considerations. When designing a PCB, however, careful layout is necessary to prevent other circuitry from degrading LDO performance. A good design places input and output capacitors as close to the LDO inputs and output as possible, and utilizes a star-ground configuration for all regulators to prevent noise-coupling through ground. Output traces should be routed to avoid close proximity to noisy nodes, particularly the SW nodes of the DC/DCs. REFBP is a noise-filtered reference, and internally has a direct connection to the linear regulator controller. Any noise injected onto REFBP will directly affect the outputs of the linear regulators, and therefore special care should be taken to ensure that no noise is injected to the outputs via REFBP. As with the LDO output capacitors, the REFBP bypass capacitor should be placed as close to the IC as possible, with short, direct connections to the star-ground. Avoid the use of via whenever possible. Noisy nodes, such as from the DC/DCs, should be routed as far away from REFBP as possible. |
Podobny numer części - ACT8847_17_06 |
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Podobny opis - ACT8847_17_06 |
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