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CS5253B-8GDP5G Scheda tecnica(PDF) 6 Page - ON Semiconductor |
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CS5253B-8GDP5G Scheda tecnica(HTML) 6 Page - ON Semiconductor |
6 / 8 page CS5253B−8 http://onsemi.com 6 Figure 15. Stability vs ESR 6 5 3 1 0 010 20 30 50 40 Capacitance ( mF) 60 70 80 90 100 4 2 VPOWER = 3.3 V VCONTROL = 5.0 V ILOAD = 0 to 3.0 A Unstable Stable Region VOUT = 2.5 V VOUT Shorted to VSENSE TJ = 0°C to 150°C APPLICATIONS NOTES THEORY OF OPERATION The CS5253B−8 linear regulator is fixed at 2.5 V at currents up to 3.0 A. The regulator is protected against short circuits, and includes a thermal shutdown circuit with hysteresis. The output, which is current limited, consists of a PNP−NPN transistor pair and requires an output capacitor for stability. VPOWER Function The CS5253B−8 utilizes a two supply approach to maximize efficiency. The collector of the power device is brought out to the VPOWER pin to minimize internal power dissipation under high current loads. VCONTROL provides for the control circuitry and the drive for the output NPN transistor. VCONTROL should be at least 1.0 V greater than the output voltage. Special care has been taken to ensure that there are no supply sequencing problems. The output voltage will not turn on until both supplies are operating. If the control voltage comes up first, the output current will be limited to about three milliamperes until the power input voltage comes up. If the power input voltage comes up first, the output will not turn on at all until the control voltage comes up. The output can never come up unregulated. The CS5253B−8 can also be used as a single supply device with the control and power inputs tied together. In this mode, the dropout will be determined by the minimum control voltage. Output Voltage Sensing The CS5253B−8 five terminal linear regulator includes a dedicated VSENSE function. This allows for true Kelvin sensing of the output voltage. This feature can virtually eliminate errors in the output voltage due to load regulation. Regulation will be optimized at the point where the sense pin is tied to the output. DESIGN GUIDELINES Remote Sense Remote sense operation can be easily obtained with the CS5253B−8 but some care must be paid to the layout and positioning of the filter capacitors around the part. The ground side of the input capacitors on the +5.0 V and +3.3 V lines and the local VOUT−to−ground output capacitor on the IC must be tied close to the ground pin of the regulator. This will establish the stability of the part. The IC ground may then be connected to ground remotely at the load, giving the ground portion remote sense operation. The VSENSE line can then be tied remotely at the positive load connection, giving the feedback remote sense operation. The remote sense lines should be Kelvin connected so as to eliminate the effect of load current voltage drop. An optional bypass capacitor may be used at the load to reduce the effect of load variations and spikes. Current Limit The internal current limit circuit limits the output current under excessive load conditions. Short Circuit Protection The device includes short circuit protection circuitry that clamps the output current at approximately 500mA less than its current limit value. This provides for a current foldback function, which reduces power dissipation under a direct shorted load. Thermal Shutdown The thermal shutdown circuitry is guaranteed by design to activate above a die junction temperature of approximately 150 °C and to shut down the regulator output. This circuitry has 25 °C of typical hysteresis, thereby allowing the regulator to recover from a thermal fault automatically. |
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