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Datenblatt-Suchmaschine für elektronische Bauteile |
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Datenblatt-Suchmaschine für elektronische Bauteile |
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CS5257A-1GT5 Datenblatt(PDF) 6 Page - Cherry Semiconductor Corporation |
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CS5257A-1GT5 Datenblatt(HTML) 6 Page - Cherry Semiconductor Corporation |
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6 / 9 page  6 Application Notes Typical Performance Characteristics: continued 74.00 76.00 77.00 0.00 1.00 5.00 7.00 Output Current (A) 75.00 73.00 72.00 6.00 2.00 3.00 4.00 8.00 VPOWER=2.05 VCONTROL=2.75V Adjust Pin Current vs Output Current The CS5257A-1 linear regulator provides adjustable volt- ages from 1.25V to 5V at currents up to 7A. The regulator is protected against short circuits, and includes a thermal shutdown circuit with hysteresis. The output, which is cur- rent limited, consists of a PNP-NPN transistor pair and requires an output capacitor for stability. A detailed pro- cedure for selecting this capacitor is included in the Stability Considerations section. VPOWER Function The CS5257A-1 utilizes a two supply approach to maxi- mize 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 power for the control circuitry and the drive for the output NPN transistor. VCONTROL should be at least 1V 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 typically limited to about 3mA 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 CS5257A-1 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 CS5257A-1 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 regula- tion. Regulation will be optimized at the point where the sense pin is tied to the output. Adjustable Operation This LDO adjustable regulator has an output voltage range of 1.25V to 5V. An external resistor divider sets the output voltage as shown in Figure 1. The regulatorÕs voltage sens- ing error amplifier maintains a fixed 1.253V reference between the output pin and the adjust pin. A resistor divider network R1 and R2 causes a fixed current to flow to ground. This current creates a voltage across R2 that adds to the 1.253V across R1 and sets the overall out- put voltage. The adjust pin current (typically 50µA) also flows through R2 and adds a small error that should be taken into account if precise adjustment of VOUT is neces- sary. The output voltage is set according to the formula: VOUT = 1.253V ´ + R2 ´ IADJ The term IADJ ´ R2 represents the error added by the adjust pin current. R1 is chosen so that the minimum load current is a least 10mA. R1 and R2 should be of the same composi- tion for best tracking over temperature. The divider resis- tors should be placed physically as close to the load as pos- sible. Figure 1: An external resistor divider sets the value of VOUT. The 1.253V reference voltage drops across R1. V SENSE V OUT V CONTROL V POWER CS5257A-1 R1 Adjust R2 R1+R2 R1 Design Guidelines Theory of Operation |
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