LM1085IS-12

LM1085 3A Low Dropout Positive Regulators June 2005 LM1085 3A Low Dropout Positive Regulators General Description The LM1085 is a series of low dropout positive voltage regulators with a maximum dropout of 1.5V at 3A of load current. It has the same pin-out as National Semiconductor’s industry standard LM317. The LM1085 is available in an adjustable version, which can set the output voltage with only two external resistors. It is also available in three fixed voltages: 3.3V, 5.0V and 12.0V. The fixed versions integrate the adjust resistors. The LM1085 circuit includes a zener trimmed bandgap reference, current limiting and thermal shutdown. The LM1085 series is available in TO-220 and TO-263 packages. Refer to the LM1084 for the 5A version, and the LM1086 for the 1.5A version. Features n n n n n Available in 3.3V, 5.0V, 12V and Adjustable Versions Current Limiting and Thermal Protection Output Current 3A Line Regulation 0.015% (typical) Load Regulation 0.1% (typical) Applications n n n n n High Efficiency Linear Regulators Battery Charger Post Regulation for Switching Supplies Constant Current Regulator Microprocessor Supply Connection Diagrams TO-220 Application Circuit 10094702 Top View TO-263 10094752 1.2V to 15V Adjustable Regulator 10094704 Top View Basic Functional Diagram, Adjustable Version 10094765 © 2005 National Semiconductor Corporation DS100947 www.national.com LM1085 Ordering Information Package 3-lead TO-263 Temperature Range −40˚C to +125˚C Part Number LM1085IS-ADJ LM1085ISX-ADJ LM1085IS-12 LM1085ISX-12 LM1085IS-3.3 LM1085ISX-3.3 LM1085IS-5.0 LM1085ISX-5.0 3-lead TO-220 −40˚C to + 125˚C LM1085IT-ADJ LM1085IT-12 LM1085IT-3.3 LM1085IT-5.0 Transport Media Rails Tape and Reel Rails Tape and Reel Rails Tape and Reel Rails Tape and Reel Rails Rails Rails Rails T03B TS3B NSC Drawing Simplified Schematic 10094734 www.national.com 2 LM1085 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Maximum Input to Output Voltage Differential LM1085-ADJ LM1085-12 LM1085-3.3 LM1085-5.0 Power Dissipation (Note 2) 29V 18V 27V 25V Internally Limited Junction Temperature (TJ)(Note 3) Storage Temperature Range Lead Temperature ESD Tolerance (Note 4) 150˚C -65˚C to 150˚C 260˚C, to 10 sec 2000V Operating Ratings (Note 1) Junction Temperature Range (TJ) (Note 3) Control Section Output Section −40˚C to 125˚C −40˚C to 150˚C Electrical Characteristics Typicals and limits appearing in normal type apply for TJ = 25˚C. Limits appearing in Boldface type apply over the entire junction temperature range for operation. Symbol VREF Parameter Reference Voltage Conditions LM1085-ADJ IOUT = 10mA, VIN−VOUT = 3V 10mA ≤IOUT ≤ IFULL LOAD,1.5V ≤ (VIN−VOUT) ≤ 15V (Note 7) LM1085-3.3 IOUT = 0mA, VIN = 5V 0 ≤ IOUT ≤IFULL LOAD, 4.8V≤ VIN ≤15V LM1085-5.0 IOUT = 0mA, VIN = 8V 0 ≤ IOUT ≤ IFULL LOAD, 6.5V ≤ VIN ≤ 20V LM1085-12 IOUT = 0mA, VIN = 15V 0 ≤ IOUT ≤ IFULL LOAD, 13.5V ≤ VIN ≤ 25V ∆VOUT Line Regulation (Note 8) LM1085-ADJ IOUT =10mA, 1.5V≤ (VIN-VOUT) ≤ 15V LM1085-3.3 IOUT = 0mA, 4.8V ≤ VIN ≤ 15V LM1085-5.0 IOUT = 0mA, 6.5V ≤ VIN ≤ 20V LM1085-12 I OUT =0mA, 13.5V ≤ VIN ≤ 25V ∆VOUT Load Regulation (Note 8) LM1085-ADJ (VIN-V OUT) = 3V, 10mA ≤ IOUT ≤ IFULL LM1085-3.3 VIN = 5V, 0 ≤ IOUT ≤ IFULL LM1085-5.0 VIN = 8V, 0 ≤ IOUT ≤ IFULL LOAD LOAD Min (Note 6) 1.238 1.225 Typ (Note 5) 1.250 1.250 Max (Note 6) 1.262 1.270 Units V V VOUT Output Voltage (Note 7) 3.270 3.235 4.950 4.900 11.880 11.760 3.300 3.300 5.000 5.000 12.000 12.000 0.015 0.035 0.5 1.0 0.5 1.0 1.0 2.0 0.1 0.2 3 7 5 10 12 24 1.3 3.330 3.365 5.050 5.100 12.120 12.240 0.2 0.2 6 6 10 10 25 25 0.3 0.4 15 20 20 35 36 72 1.5 V V V V V V % % mV mV mV mV mV mV % % mV mV mV mV mV mV V LOAD LM1085-12 VIN = 15V, 0 ≤ IOUT ≤ IFULL Dropout Voltage (Note 9) LOAD LM1085-ADJ, 3.3, 5, 12 ∆VREF, ∆VOUT = 1%, IOUT = 3A 3 www.national.com LM1085 Electrical Characteristics (Continued) Typicals and limits appearing in normal type apply for TJ = 25˚C. Limits appearing in Boldface type apply over the entire junction temperature range for operation. Parameter Current Limit LM1085-ADJ VIN−VOUT = 5V VIN−VOUT = 25V LM1085-3.3 VIN = 8V LM1085-5.0 VIN = 10V LM1085-12 VIN = 17V Minimum Load Current (Note 10) Quiescent Current LM1085-ADJ VIN −VOUT = 25V LM1085-3.3 VIN ≤ 18V LM1085-5.0 VIN ≤ 20V LM1085-12 VIN ≤ 25V Thermal Regulation Ripple Rejection TA = 25˚C, 30ms Pulse fRIPPLE = 120Hz, COUT = 25µF Tantalum, IOUT = 3A LM1085-ADJ, CADJ = 25µF, (VIN−VO) = 3V LM1085-3.3, VIN = 6.3V LM1085-5.0, VIN = 8V LM1085-12 VIN = 15V Adjust Pin Current Adjust Pin Current Change Temperature Stability Long Term Stability RMS Output Noise (% of VOUT) Thermal Resistance Junction-to-Case TA=125˚C, 1000Hrs 10Hz ≤ f≤ 10kHz 3-Lead TO-263: Control Section/Output Section 3-Lead TO-220: Control Section/Output Section LM1085 10mA ≤ IOUT ≤ IFULL LOAD, Symbol ILIMIT Conditions Min (Note 6) 3.2 0.2 3.2 3.2 3.2 Typ (Note 5) 5.5 0.5 5.5 5.5 5.5 5.0 5.0 5.0 5.0 .004 Max (Note 6) Units A A A A A 10.0 10.0 10.0 10.0 0.02 mA mA mA mA %/W dB dB dB dB 120 5 µA µA % 1.0 % % 0.7/3.0 0.7/3.0 ˚C/W ˚C/W 60 60 60 54 75 72 68 60 55 1.5V ≤ VIN−VOUT ≤ 25V 0.2 0.5 0.3 0.003 Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics. Note 2: Power dissipation is kept in a safe range by current limiting circuitry. Refer to Overload Recovery in Application Notes. Note 3: The maximum power dissipation is a function of TJ(max) , θJA, and TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJ(max)–T A)/θJA. All numbers apply for packages soldered directly into a PC board. Refer to Thermal Considerations in the Application Notes. Note 4: For testing purposes, ESD was applied using human body model, 1.5kΩ in series with 100pF. Note 5: Typical Values represent the most likely parametric norm. Note 6: All limits are guaranteed by testing or statistical analysis. Note 7: IFULL LOAD is defined in the current limit curves. The IFULL LOAD Curve defines the current limit as a function of input-to-output voltage. Note that 30W power dissipation for the LM1085 is only achievable over a limited range of input-to-output voltage. Note 8: Load and line regulation are measured at constant junction temperature, and are guaranteed up to the maximum power dissipation of 30W. Power dissipation is determined by the input/output differential and the output current. Guaranteed maximum power dissipation will not be available over the full input/output range. Note 9: Dropout voltage is specified over the full output current range of the device. Note 10: The minimum output current required to maintain regulation. www.national.com 4 LM1085 Typical Performance Characteristics Dropout Voltage vs. Output Current Short-Circuit Current vs. Input/Output Difference 10094763 10094768 Percent Change in Output Voltage vs. Temperature Adjust Pin Current vs. Temperature 10094799 10094798 Maximum Power Dissipation vs. Temperature Ripple Rejection vs. Frequency (LM1085-Adj.) 10094743 10094770 5 www.national.com LM1085 Typical Performance Characteristics Ripple Rejection vs. Output Current (LM1085-Adj.) (Continued) Line Transient Response 10094744 10094772 Load Transient Response 10094771 www.national.com 6 LM1085 Application Note GENERAL Figure 1 shows a basic functional diagram for the LM1085Adj (excluding protection circuitry) . The topology is basically that of the LM317 except for the pass transistor. Instead of a Darlingtion NPN with its two diode voltage drop, the LM1085 uses a single NPN. This results in a lower dropout voltage. The structure of the pass transistor is also known as a quasi LDO. The advantage a quasi LDO over a PNP LDO is its inherently lower quiescent current. The LM1085 is guaranteed to provide a minimum dropout voltage 1.5V over temperature, at full load. STABILITY CONSIDERATION Stability consideration primarily concern the phase response of the feedback loop. In order for stable operation, the loop must maintain negative feedback. The LM1085 requires a certain amount series resistance with capacitive loads. This series resistance introduces a zero within the loop to increase phase margin and thus increase stability. The equivalent series resistance (ESR) of solid tantalum or aluminum electrolytic capacitors is used to provide the appropriate zero (approximately 500 kHz). The Aluminum electrolytic are less expensive than tantalums, but their ESR varies exponentially at cold temperatures; therefore requiring close examination when choosing the desired transient response over temperature. Tantalums are a convenient choice because their ESR varies less than 2:1 over temperature. The recommended load/decoupling capacitance is a 10uF tantalum or a 50uF aluminum. These values will assure stability for the majority of applications. The adjustable versions allows an additional capacitor to be used at the ADJ pin to increase ripple rejection. If this is done the output capacitor should be increased to 22uF for tantalums or to 150uF for aluminum. Capacitors other than tantalum or aluminum can be used at the adjust pin and the input pin. A 10uF capacitor is a reasonable value at the input. See Ripple Rejection section regarding the value for the adjust pin capacitor. It is desirable to have large output capacitance for applications that entail large changes in load current (microprocessors for example). The higher the capacitance, the larger the available charge per demand. It is also desirable to provide low ESR to reduce the change in output voltage: ∆V = ∆I x ESR It is common practice to use several tantalum and ceramic capacitors in parallel to reduce this change in the output voltage by reducing the overall ESR. Output capacitance can be increased indefinitely to improve transient response and stability. RIPPLE REJECTION Ripple rejection is a function of the open loop gain within the feed-back loop (refer to Figure 1 and Figure 2). The LM1085 exhibits 75dB of ripple rejection (typ.). When adjusted for voltages higher than VREF, the ripple rejection decreases as function of adjustment gain: (1+R1/R2) or VO/VREF. Therefore a 5V adjustment decreases ripple rejection by a factor of four (−12dB); Output ripple increases as adjustment voltage increases. However, the adjustable version allows this degradation of ripple rejection to be compensated. The adjust terminal can be bypassed to ground with a capacitor (CADJ). The impedance of the CADJ should be equal to or less than R1 at the desired ripple frequency. This bypass capacitor prevents ripple from being amplified as the output voltage is increased. 1/(2π*fRIPPLE*CADJ) ≤ R1 LOAD REGULATION The LM1085 regulates the voltage that appears between its output and ground pins, or between its output and adjust pins. In some cases, line resistances can introduce errors to the voltage across the load. To obtain the best load regulation, a few precautions are needed. 10094765 FIGURE 1. Basic Functional Diagram for the LM1085, excluding Protection circuitry OUTPUT VOLTAGE The LM1085 adjustable version develops at 1.25V reference voltage, (VREF), between the output and the adjust terminal. As shown in figure 2, this voltage is applied across resistor R1 to generate a constant current I1. This constant current then flows through R2. The resulting voltage drop across R2 adds to the reference voltage to sets the desired output voltage. The current IADJ from the adjustment terminal introduces an output error . But since it is small (120uA max), it becomes negligible when R1 is in the 100Ω range. For fixed voltage devices, R1 and R2 are integrated inside the devices. 10094717 FIGURE 2. Basic Adjustable Regulator 7 www.national.com LM1085 Application Note (Continued) Figure 3 shows a typical application using a fixed output regulator. Rt1 and Rt2 are the line resistances. VLOAD is less than the VOUT by the sum of the voltage drops along the line resistances. In this case, the load regulation seen at the RLOAD would be degraded from the data sheet specification. To improve this, the load should be tied directly to the output terminal on the positive side and directly tied to the ground terminal on the negative side. adjustment terminal. The adjust pin can take a transient signal of ± 25V with respect to the output voltage without damaging the device. When an output capacitor is connected to a regulator and the input is shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage of the regulator, and rate of decrease of VIN. In the LM1085 regulator, the internal diode between the output and input pins can withstand microsecond surge currents of 10A to 20A. With an extremely large output capacitor (≥1000 µf), and with input instantaneously shorted to ground, the regulator could be damaged. In this case, an external diode is recommended between the output and input pins to protect the regulator, shown in Figure 5. 10094718 FIGURE 3. Typical Application using Fixed Output Regulator When the adjustable regulator is used (Figure 4), the best performance is obtained with the positive side of the resistor R1 tied directly to the output terminal of the regulator rather than near the load. This eliminates line drops from appearing effectively in series with the reference and degrading regulation. For example, a 5V regulator with 0.05Ω resistance between the regulator and load will have a load regulation due to line resistance of 0.05Ω x IL. If R1 (= 125Ω) is connected near the load the effective line resistance will be 0.05Ω (1 + R2/R1) or in this case, it is 4 times worse. In addition, the ground side of the resistor R2 can be returned near the ground of the load to provide remote ground sensing and improve load regulation. 10094715 FIGURE 5. Regulator with Protection Diode OVERLOAD RECOVERY Overload recovery refers to regulator’s ability to recover from a short circuited output. A key factor in the recovery process is the current limiting used to protect the output from drawing too much power. The current limiting circuit reduces the output current as the input to output differential increases. Refer to short circuit curve in the curve section. During normal start-up, the input to output differential is small since the output follows the input. But, if the output is shorted, then the recovery involves a large input to output differential. Sometimes during this condition the current limiting circuit is slow in recovering. If the limited current is too low to develop a voltage at the output, the voltage will stabilize at a lower level. Under these conditions it may be necessary to recycle the power of the regulator in order to get the smaller differential voltage and thus adequate start up conditions. Refer to curve section for the short circuit current vs. input differential voltage. THERMAL CONSIDERATIONS ICs heats up when in operation, and power consumption is one factor in how hot it gets. The other factor is how well the heat is dissipated. Heat dissipation is predictable by knowing the thermal resistance between the IC and ambient (θJA). Thermal resistance has units of temperature per power (C/ W). The higher the thermal resistance, the hotter the IC. The LM1085 specifies the thermal resistance for each package as junction to case (θJC). In order to get the total resistance to ambient (θJA), two other thermal resistance 10094719 FIGURE 4. Best Load Regulation using Adjustable Output Regulator PROTECTION DIODES Under normal operation, the LM1085 regulator does not need any protection diode. With the adjustable device, the internal resistance between the adjustment and output terminals limits the current. No diode is needed to divert the current around the regulator even with a capacitor on the www.national.com 8 LM1085 Application Note (Continued) must be added, one for case to heat-sink (θCH) and one for heatsink to ambient (θHA). The junction temperature can be predicted as follows: TJ = TA + PD (θJC + θCH + θHA) = TA + PD θJA TJ is junction temperature, TA is ambient temperature, and PD is the power consumption of the device. Device power consumption is calculated as follows: IIN = IL + IG PD = (VIN−VOUT) IL + VINIG Figure 6 shows the voltages and currents which are present in the circuit. 10094716 FIGURE 6. Power Dissipation Diagram Once the devices power is determined, the maximum allowable (θJA(max)) is calculated as: θJA(max) = TR(max)/PD = TJ(max − TA(max))/PD The LM1085 has different temperature specifications for two different sections of the IC: the control section and the output section. The Electrical Characteristics table shows the junction to case thermal resistances for each of these sections, while the maximum junction temperatures (TJ(max)) for each section is listed in the Absolute Maximum section of the datasheet. TJ(max) is 125˚C for the control section, while TJ(max) is 150˚C for the output section. θJA(max) should be calculated separately for each section as follows: θJA (max, CONTROL SECTION) = (125˚C - TA(max))/PD θJA(max, OUTPUT SECTION) = (150˚C - TA(max))/PD The required heat sink is determined by calculating its required thermal resistance (θHA(max)). θHA(max) = θJA(max) − (θJC + θCH) θHA(max) should also be calculated twice as follows: θHA(max) = θJA (max, CONTROL SECTION) - (θJC (CONTROL SECTION) + θCH) θHA(max)=θJA(max, OUTPUT SECTION) - (θJC(OUTPUT SECTION) + θCH) If thermal compound is used, θCH can be estimated at 0.2 C/W. If the case is soldered to the heat sink, then a θCH can be estimated as 0 C/W. After, θHA(max) is calculated for each section, choose the lower of the two θHA(max) values to determine the appropriate heat sink. If PC board copper is going to be used as a heat sink, then Figure 7 can be used to determine the appropriate area (size) of copper foil required. 10094764 FIGURE 7. Heat sink thermal Resistance vs Area 9 www.national.com LM1085 Typical Applications 10094767 5V to 3.3V, 1.5A Regulator Battery Charger 10094754 10094750 Adjustable @ 5V Adjustable Fixed Regulator 10094755 10094756 Regulator with Reference 10094752 1.2V to 15V Adjustable Regulator 10094757 High Current Lamp Driver Protection 10094753 5V Regulator with Shutdown www.national.com 10 LM1085 Typical Applications (Continued) 10094761 Automatic Light control 10094759 Battery Backup Regulated Supply 10094762 Generating Negative Supply voltage 10094760 Ripple Rejection Enhancement 10094758 Remote Sensing 11 www.national.com LM1085 Physical Dimensions inches (millimeters) unless otherwise noted 3-Lead TO-263 NS Package Number TS3B 3-Lead TO-220 NS Package Number T03B www.national.com 12 LM1085 3A Low Dropout Positive Regulators Notes National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. 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