LT1033 - 3A. Negative Adjustable Regulator - Linear Technology

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LT1033 TYPICAL PERFORMANCE CHARACTERISTICS U W Ripple Rejection Ripple Rejection Ripple Rejection 100 100 100 RIPPLE REJECTION (dB) 80 60 40 C ADJ = 10µF C ADJ = 0 V IN – V OUT = 5V 20 I L = 500mA f = 120Hz T J = 25°C 0 0 –10 –20 –30 –40 OUTPUT VOLTAGE (V) RIPPLE REJECTION (dB) 80 60 40 C ADJ = 0 C ADJ = 10µF V IN = –15V 20 V OUT = –10V I L = 500mA T J = 25°C 0 10 100 1k 10k 100k 1M FREQUENCY (Hz) RIPPLE REJECTION (dB) 80 60 40 C ADJ = 10µF C ADJ = 0 V IN = –15V 20 V OUT = –10V f = 120Hz T J = 25°C 0 0.01 0.1 1 10 OUTPUT CURRENT (A) LT1033 • G05 LT1033 • G06 LT1033 • G07 OUTPUT IMPEDANCE (Ω) 101 100 10 –1 10–2 Output Impedance Line Transient Response Load Transient Response V IN = –15V V OUT = –10V I L = 500mA C L = 1µF T J = 25°C C ADJ = 0 C ADJ = 10µF 10–3 10 100 1k 10k 100k 1M FREQUENCY (Hz) OUTPUT VOLTAGE DEVIATION (V) INPUT VOLTAGE CHANGE (V) 0.8 0.6 0.4 0.2 0 –0.2 –0.4 0 –0.5 –1.0 C ADJ = 0 C ADJ = 10µF V OUT = –10V I L = 50mA T J = 25°C C L = 1µF 0 10 20 TIME (µs) 30 40 OUTPUT VOLTAGE DEVIATION (V) LOAD CURRENT (A) 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 0 –0.5 –1.0 –1.5 C ADJ = 0 C ADJ = 10µF V IN = –15V V OUT = –10V I NL = 50mA T J = 25°C C L = 1µF 0 10 20 TIME (µs) 30 40 LT1033 • G08 LT1033 • G09 LT1033 • G10 Load Regulation* Guaranteed Minimum Output Current Adjustment Current OUTPUT VOLTAGE DEVIATION (%) 0.8 0.4 0 –0.4 –0.8 OUTPUT CURRENT (A) 5 4 3 2 1 ADJUSTMENT CURRENT (µA) 80 75 70 65 60 55 0 0.8 1.6 2.4 3.2 4.0 OUTPUT CURRENT (A) *THE LT1033 HAS LOAD REGULATION COMPENSATION WHICH MAKES THE TYPICAL UNIT READ CLOSE TO ZERO. THIS BAND REPRESENTS THE TYPICAL PRODUCTION SPREAD 0 0 5 10 15 20 25 30 35 INPUT-OUTPUT DIFFERENTIAL (V) LT1033 • G12 50 –75 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) LT1033 • G13 LT1033 • G11 4 1033fc
LT1033 APPLICATIONS INFORMATION Output Voltage The output voltage is determined by two external resistors, R1 and R2 (see Figure 1). The exact formula for the output voltage is: V ⎛ R2⎞ = V ⎜1+ ⎟ + I ( R2) ⎝ R1⎠ OUT REF ADJ Where: V REF = Reference Voltage, I ADJ = Adjustment Pin Current. In most applications, the second term is small enough to be ignored, typically about 0.5% of V OUT . In more critical applications, the exact formula should be used, with I ADJ equal to 65µA. Solving for R2 yields: VOUT – V R2 = VREF – I R1 + C1 R2 10µF I ADJ C3 C2 2µF 5µF V REF R1 ADJ –V IN V IN V OUT –V OUT LT1033 LT1033 • F01 EXAMPLE: 1. A PRECISION 10V REGULATOR TO SUPPLY UP TO 3A LOAD CURRENT. A. SELECT R1 = 100Ω TO MINIMIZE EFFECT OF I ADJ B. CALCULATE R2 = V OUT – V REF 10V – 1.25V = = 704Ω V REF 1.25V – I R1 ADJ 100Ω – 65µA + + REF ADJ U W U U Smaller values of R1 and R2 will reduce the influence of I ADJ on the output voltage, but the no-load current drain on the regulator will be increased. Typical values for R1 are between 100Ω and 300Ω, giving 12.5mA and 4.2mA no-load current respectively. There is an additional consideration in selecting R1, the minimum load current specification of the regulator. The operating current of the LT1033 flows from input to output. If this current is not absorbed by the load, the output of the regulator will rise above the regulated value. The current drawn by R1 and R2 is normally high enough to absorb the current, but care must be taken in no-load situations where R1 and R2 have high values. The maximum value for the operating current, Figure 1 which must be absorbed, is 5mA for the LT1033. If inputoutput voltage differential is less than 10V, the operating current that must be absorbed drops to 3mA. Capacitors and Protection Diodes An output capacitor, C3, is required to provide proper frequency compensation of the regulator feedback loop. A 2µF or larger solid tantalum capacitor is generally sufficient for this purpose if the 1MHz impedance of the capacitor is 1Ω or less. High Q capacitors, such as Mylar, are not recommended because their extremely low ESR (effective series resistance) can drastically reduce phase margin. When these types of capacitors must be used because of other considerations, add a 0.5Ω carbon resistor in series with 1µF. Aluminum electrolytic capacitors may be used, but the minimum value should be 25µF to ensure a low impedance at 1MHz. The output capacitor should be located within a few inches of the regulator to keep lead impedance to a minimum. The following caution should be noted: if the output voltage is greater than 6V and an output capacitor greater than 20µF has been used, it is possible to damage the regulator if the input voltage becomes shorted, due to the output capacitor discharging into the regulator. This can be prevented by using diode D1 (see Figure 2) between the input and the output. The input capacitor, C2, is only required if the regulator is more than 4 inches from the raw supply filter capacitor. Bypassing the Adjustment Pin The adjustment pin of the LT1033 may be bypassed with a capacitor to ground, C1, to reduce output ripple, noise, and impedance. These parameters scale directly with output voltage if the adjustment pin is not bypassed. A bypass capacitor reduces ripple, noise and impedance to that of a 1.25V regulator. In a 15V regulator for example, these parameters are improved by 15V/1.25V = 12 to 1. This improvement holds only for those frequencies where the impedance of the bypass capacitor is less than R1. Ten microfarads is generally sufficient for 60Hz power line applications where the ripple frequency is 120Hz, since X C = 130Ω. The capacitor should have a voltage rating at least as high as the output voltage of the regulator. Values 1033fc 5
Page 1 and 2: NOT RECOMMENDED FOR NEW DESIGNS Con
Page 3: ELECTRICAL CHARACTERISTICS (Note 2)
Page 7 and 8: + LT1033 TYPICAL APPLICATIO S The o
Page 9 and 10: LT1033 PROGRAM RESISTOR SELECTIO U
Page 11 and 12: LT1033 PACKAGE DESCRIPTION U P Pack

LT1033 - 3A. Negative Adjustable Regulator - Linear Technology

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