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GRM42-6X5R475K10 Datasheet(PDF) 5 Page - Impala Linear Corporation |
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GRM42-6X5R475K10 Datasheet(HTML) 5 Page - Impala Linear Corporation |
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5 / 16 page  150mA SOT-23 Ultra Low Noise CMOS RF-LDO™ Regulator Impala Linear Corporation 5 (408) 574-3939 www.impalalinear.com April 1999 ILC7082 1.3 OPERATION The ILC7082 LDO design is based on an advanced circuit configuration for which patent protection has been applied. Typically it is very difficult to drive a capacitive output with an amplifier. The output capacitance produces a pole in the feedback path, which upsets the carefully tailored dominant pole of the internal amplifier. Traditionally the pole of the output capacitor has been “eliminated” by reducing the out- put impedance of the regulator such that the pole of the output capacitor is moved well beyond the gain bandwidth product of the regulator. In practice, this is difficult to do and still maintain high frequency operation. Typically the output impedance of the regulator is not simply resistive, such that the reactive output impedance interacts with the reactive impedance of the load resistance and capacitance. In addi- tion, it is necessary to place the dominant pole of the circuit at a sufficiently low frequency such that the gain of the reg- ulator has fallen below unity before any of the complex interactions between the output and the load occur. The ILC7082 does not try to eliminate the output pole, but incor- porates it into the stability scheme. The load and output capacitor forms a pole, which rolls off the gain of the regu- lator below unity. In order to do this the output impedance of the regulator must be high, looking like a current source. The output stage of the regulator becomes a transconduc- tance amplifier, which converts a voltage to a current with a substantial output impedance. The circuit which drives the transconductance amplifier is the error amplifier, which compares the regulator output to the band gap reference and produces an error voltage as the input to the transcon- ductance amplifier. The error amplifier has a dominant pole at low frequency and a “zero” which cancels out the effects of the pole. The zero allows the regulator to have gain out to the frequency where the output pole continues to reduce the gain to unity. The configuration of the poles and zero are shown in figure 1. Instead of powering the critical circuits from the unregulated input voltage, the CMOS RF LDO powers the internal circuits such as the bandgap, the error amplifier and most of the transconductance amplifier from the boot strapped regulated output voltage of the regulator. This technique offers extremely high ripple rejection and excellent line transient response. A block diagram of the regulator circuit used in the ILC7082 is shown in figure 2 (following page), which shows the input- to-output isolation and the cascaded sequence of amplifiers that implement the pole-zero scheme outlined above. The ILC7082 is designed in a CMOS process with some minor additions, which allow the circuit to be used at input voltages up to 13V. The resulting circuit exceeds the fre- quency response of traditional bipolar circuits. The ILC7082 is very tolerant of output load conditions with the inclusion of both short circuit and thermal overload protection. The device has a very low dropout voltage, typically a linear response of 1mV per milliamp of load current, and none of the quasi-saturation characteristics of a bipolar output devices. All the good features of the frequency response and regulation are valid right to the point where the regula- tor goes out of regulation in a 4 millivolt transition region. Because there is no base drive, the regulator is capable of providing high current surges while remaining in regulation. This is shown in the high peak current of 500mA which allows for the ILC7082 to be used in systems that require short burst mode operation. ELECTRICAL CHARACTERISTICS ILC7082AIM5 (continued) Figure 1: ILC7082 RF LDO frequency response ON/OFF GND V OUT V IN C NOISE FEEDBACK BANDGAP REFERENCE V REFD ERROR AMPLIFIER TRANS- CONDUCTANCE AMPLIFIER INTERNAL V DD Figure 2: ILC7082 RF LDO regulator block diagram |
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