LM2825 Integrated Power Supply 1A DC-DC Converter
LM2825 Integrated Power Supply 1A DC-DC Converter
The LM2825 is a complete 1A DC-DC Buck converter packaged in a 24-lead molded Dual-In-Line integrated circuit package. Contained within the package are all the active and passive components for a high efficiency step-down (buck) switching regulator. Available in fixed output voltages of 3.3V, 5V and 12V, as well as two adjustable versions, these devices can provide up to 1A of load current with fully guaranteed electrical specifications. Self-contained, this converter is also fully protected from output fault conditions, such as excessive load current, short circuits, or excessive temperatures.
n n n n n n n n n n n Minimum design time required 3.3V, 5V and 12V fixed output versions Two adjustable versions allow 1.23V to 15V outputs Wide input voltage range, up to 40V Low-power standby mode, IQ typically 65 µA High efficiency, typically 80% ± 4% output voltage tolerance Excellent line and load regulation TTL shutdown capability/programmable Soft-start Thermal shutdown and current limit protection −40˚C to +85˚C ambient temperature range
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n No external components required (fixed output voltage versions) n Integrated circuit reliability n MTBF over 20 million hours n Radiated EMI meets Class B stipulated by CISPR 22 n High power density, 35 W/in3 n 24-pin DIP package profile (1.25 x 0.54 x 0.26 inches)
n n n n n Simple high-efficiency step-down (buck) regulator On-card switching regulators Efficient pre-regulator for linear regulators Distributed power systems DC/DC module replacement
(Fixed output voltage versions)
“NC (Do not use)” pins: See Figure 11.
Order Number LM2825N-3.3, LM2825N-5.0, LM2825N-12, LM2825N-ADJ or LM2825HN-ADJ See NS Package Number NA24F
Radiated emission of electromagnetic fields is measured at 10m distance. The emission levels are within the Class B limits stipulated by CISPR 22. 30. . . .230 MHz 230. . . .1000 MHz 1. . . .10 GHz 30 dB µV/m 37 dB µV/m 46 dB µV/m
© 1997 National Semiconductor Corporation
Absolute Maximum Ratings
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Maximum Input Supply (VIN) SD/SS Pin Input Voltage (Note 2) Output Pin Voltage (3.3V, 5.0V and ADJ) (12V and H-ADJ) ADJ Pin Voltage (ADJ, H-ADJ only) Power Dissipation Storage Temperature Range +45V 6V −1V ≤ V ≤ 9V −1V ≤ V ≤ 16V −0.3V ≤ V ≤ 25V Internally Limited −40˚C to +125˚C
ESD Susceptibility Human Body Model (Note 3) Lead Temperature (Soldering 10 sec.)
2 kV 260˚C
Ambient Temperature Range Junction Temperature Range Input Supply Voltage (3.3V version) Input Supply Voltage (5V version) Input Supply Voltage (12V version) Input Supply Voltage (-ADJ, H-ADJ) −40˚C ≤ TA ≤ +85˚C −40˚C ≤ TJ ≤ +125˚C 4.75V to 40V 7V to 40V 15V to 40V 4.5V to 40V
LM2825-3.3 Electrical Characteristics
(Note 4) Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Temperature Range. Test Circuit Figure 2. Conditions LM2825-3.3 Typical (Note 6) Limit (Note 7) V 3.168/3.135 3.432/3.465 Line Regulation Load Regulation Output Ripple Voltage 4.75V ≤ VIN ≤ 40V ILOAD = 100 mA 0.1A ≤ ILOAD ≤ 1A VIN = 12V VIN = 12V, ILOAD = 1A VIN = 12V, ILOAD = 0.5A 1.5 8 40 75 V(min) V(max) mV mV mV p-p % Units (Limits)
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4.75V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A
LM2825-5.0 Electrical Characteristics
(Note 4) Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Temperature Range. Test Circuit Figure 2. Conditions LM2825-5.0 Typical (Note 6) Limit (Note 7) V 4.800/4.750 5.200/5.250 Line Regulation Load Regulation Output Ripple Voltage 7V ≤ VIN ≤ 40V ILOAD = 100 mA 0.1A ≤ ILOAD ≤ 1A VIN = 12V VIN = 12V, ILOAD = 1A VIN = 12V, ILOAD = 0.5A 2.7 8 40 80 V(min) V(max) mV mV mV p-p % Units (Limits)
7V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A
LM2825-12 Electrical Characteristics (Note 4) Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Temperature Range. Test Circuit Figure 2.
Symbol Parameter Conditions LM2825-12 Typical (Note 6) VOUT Output Voltage 15V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 0.75A 12.0 11.52/11.40 12.48/12.60 Line Regulation Load Regulation Output Ripple Voltage η Efficiency 15V ≤ VIN ≤ 40V ILOAD = 100 mA 0.1A ≤ ILOAD ≤ 0.75A VIN = 24V VIN = 24V, ILOAD = 1A VIN = 24V, ILOAD = 0.5A 8.5 12 100 87 Limit (Note 7) V V(min) V(max) mV mV mV p-p % Units (Limits)
LM2825-ADJ Electrical Characteristics (Note 5) Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Temperature Range. Test Circuit Figure 3.
Symbol Parameter Conditions LM2825-ADJ Typical (Note 6) VADJ Adjust Pin Voltage 4.5V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A 1.23V ≤ VOUT ≤ 8V η Efficiency VIN = 12V, ILOAD = 0.5A VOUT Programmed for 3V. See Circuit of Figure 3 74 1.230 1.193/1.180 1.267/1.280 Limit (Note 7) V V(min) V(max) % Units (Limits)
LM2825H-ADJ Electrical Characteristics (Note 5) Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Temperature Range. Test Circuit Figure 3.
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Symbol Parameter Conditions LM2825H-ADJ Typical (Note 6) VADJ Adjust Pin Voltage 9V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 0.55A 7V ≤ VOUT ≤ 15V η Efficiency VIN = 24V, ILOAD = 0.5A VOUT Programmed for 12V. See Circuit of Figure 3 87 1.230 1.193/1.180 1.267/1.280 Limit (Note 7) V V(min) V(max) % Units (Limits)
All Output Voltage Versions Electrical Characteristics
Specifications with standard type face are for TA = 25˚C, and those with boldface type apply over full Operating Range. Unless otherwise specified, VIN = 12V for 3.3V, 5.0V and ADJ versions, VIN = 24V for 12V and H-ADJ versions, ILOAD = 100 mA. Symbol Parameter Conditions LM2825-XX Typical (Note 6) ICL DC Output Current Limit RL = 0Ω 1.4 1.2 2.4 IQ Operating Quiescent Current Standby Quiescent Current Adjust Pin Bias Current Oscillator Frequency Thermal Resistance Shutdown Threshold Voltage Low (Shutdown Mode) VSS ISD ISS Soft-start Voltage Shutdown Current Soft-start Current High (Soft-start Mode) VOUT = 20% of Nominal Output Voltage VOUT = 100% of Nominal Output Voltage VSHUTDOWN = 0.5V (Note 8) VSOFT-START = 2.5V (Note 8) 1.6 5 2 3 5 10 µA µA(max) µA µA(max) SD/SS Pin = 3.1V (Note 8) SD/SS Pin = 0V (Note 8) IADJ fO θJA VSD Adjustable Versions Only, VFB = 1.3V (Note 9) Junction to Ambient (Note 10) 6 50/100 150 30 1.3 0.6 2.0 5 10 65 200 Limit (Note 7) A A(min) A(max) mA mA(max) µA µA(max) nA nA(max) kHz ˚C/W V V(max) V(min) V Units (Limits)
SHUTDOWN/SOFT-START CONTROL Test Circuit Figure 2
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 do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: Voltage internally clamped. If clamp voltage is exceeded, limit current to a maximum of 5 mA. Note 3: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin. Note 4: When the LM2825 is used as shown in Figure 2 test circuit, system performance will be as shown in Electrical Characteristics. Note 5: When the LM2825 is used as shown in Figure 3 test circuit, system performance will be as shown in Electrical Characteristics. Note 6: Typical numbers are at 25˚C and represent the most likely norm. Note 7: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face) when output current is limited to the value given in the temperature derating curves. See the application section for curves. All limits at temperature extremes are guaranteed using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
... of the circuit. The graph starts out very flat, and while there is a current and voltage in the circuit, there seems ... is the case, the graph will start to go horizontal. Prediction graphs Independent variable - Voltage Dependant Variable - Current, Brightness of bulb, resistance ( ... . The graph will start to curve more, and have a steeper gradient the greater the voltage, and current are. This is ...
Note 8: ILOAD = 0A. Note 9: The switching frequency is reduced when the second stage current limit is activated. The amount of reduction is determined by the severity of current overload. Note 10: Junction to ambient thermal resistance (no external heat sink) for the DIP-24 package with the leads soldered to a printed circuit board with (1 oz.) copper area of approximately 2 in2.
Typical Performance Characteristics (Circuits of Figure 2 and Figure 3) Unless otherwise specified, VIN = 12V for 3.3V, 5.0V and ADJ versions, VIN = 24V for 12V and H-ADJ versions, ILOAD = 100 mA, TA = 25˚C
Normalized Output Voltage Efficiency Dropout Voltage
Output Ripple Voltage
Operating Quiescent Current
Shutdown Quiescent Current
DS012661-11 DS012661-9 DS012661-10
Typical Performance Characteristics (Circuits of Figure 2 and Figure 3) Unless otherwise specified, VIN = 12V for 3.3V, 5.0V and ADJ versions, VIN = 24V for 12V and H-ADJ versions, ILOAD = 100 mA, TA = 25˚C (Continued)
Soft-start Shutdown /Soft-start Current Soft-start Response
Switch Current Limit
Adjust Pin Bias Current
Load Transient Response for Continuous Mode VIN = 20V, VOUT = 5V, IL = 250 mA to 750 mA
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Load Transient Response for Discontinuous Mode VIN = 20V, VOUT = 5V, IL = 40 mA to 140 mA
A: Output Voltage 100 mV/div (AC) B: 250 mA to 750 mA Load Pulse Horizontal Time Base: 200 µs/div
A: Output Voltage 100 mV/div (AC) B: 40 mA to 140 mA Load Pulse Horizontal Time Base: 200 µs/div
FIGURE 1. Typical Load Transient Response
*Optional—Required if package is more than 6″ away from main filter or bypass capacitor. **Optional Soft-start Capacitor
VIN = 40V (max) VOUT = 3.3V or 5V @ 1A or 12V @ 0.75A
FIGURE 2. Standard Test Circuit (Fixed Output Voltage Versions)
*Optional—Required if package is more than 6″ away from main filter or bypass capacitor. **Optional Soft-start Capacitor ***Optional—See Application Information.
VIN = 40V (max) VOUT = 1.23V to 8V (LM2825-ADJ) 7V to 15V (LM2825H-ADJ) ILOAD = IMAX (See derating curves)
FIGURE 3. Standard Test Circuit (Adjustable Output Voltage Versions)
PROGRAMMING OUTPUT VOLTAGE (Selecting R1 and R2 as shown in Figure 3) The LM2825 is available in two adjustable output versions. The LM2825-ADJ has been optimized for output voltages between 1.23V and 8V, while the LM2825H-ADJ covers the output voltage range of 7V to 15V. Both adjustable versions are set in the following way.
Select R2 with the following equation.
When programming VOUT, keep in mind that VIN must be greater than VOUT + 2V for proper operation. OPTIONAL EXTERNAL COMPONENTS SOFT-START CAPACITOR CSS: A capacitor on this pin provides the regulator with a Soft-start feature (slow start-up).
The current drawn from the source starts out at a low average level with narrow pulses, and ramps up in a controlled manner as the pulses expand to their steady-state width. This reduces the startup current considerably, and delays and slows down the output voltage rise time.
Select a value for R1 between 240Ω and 1.5 kΩ. The lower resistor values minimize noise pickup at the sensitive adjust pin. (For lowest temperature coefficient and the best stability with time, use 1% metal film resistors.)
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(Continued) VOUT 2 3 4 5 6 7 8 7 8 9 10 11 12 13 14 15 R2 LM2825-ADJ 630 1.43k 2.26k 3.09k 3.92k 4.75k 5.49k LM2825H-ADJ 4.75k 5.49k 6.34k 7.15k 8.06k 8.87k 9.53k 10.5k 11.3k 2700 pF 2200 pF 1800 pF 1500 pF 1000 pF 820 pF 680 pF 680 pF 680 pF N/A N/A 2700 pF 2700 pF 2200 pF 1800 pF 1500 pF CFF
It is especially useful in situations where the input power source is limited in the amount of current it can deliver, since you avoid loading down this type of power supply. Under some operating conditions, a Soft-start capacitor is required for proper operation. Figure 5 indicates the input voltage and ambient temperature conditions for which a Soft-start capacitor may be required. This curve is typical for full guaranteed output current and can be used as a guideline. As the output current decreases, the operating area requiring a Soft-start capacitor decreases. Capacitor values between 0.1 µF and 1 µF are recommended. Tantalum or ceramic capacitors are appropriate for this application. INPUT CAPACITOR CIN: An optional input capacitor is required if the package is more than 6″ away from the main filter or bypass capacitor. A low ESR aluminum or tantalum bypass capacitor is recommended between the input pin and ground to prevent large voltage transients from appearing at the input. In addition, to be conservative, the RMS current rating of the input capacitor should be selected to be at least 1⁄2 the DC load current. With a 1A load, a capacitor with a RMS current rating of at least 500 mA is recommended. The voltage rating should be approximately 1.25 times the maximum input voltage. With a nominal input voltage of 12V, an aluminum electrolytic capacitor (Panasonic HFQ series or Nichicon PL series or equivalent) with a voltage rating greater than 15V (1.25 x VIN) would be needed. Solid tantalum input capacitors should only be used where the input source is impedance current limited. High dV/dt applied at the input can cause excessive charge current through low ESR tantalum capacitors. This high charge current can result in shorting within the capacitor. It is recommended that they be surge current tested by the manufacturer.The TPS series available from AVX, and the 593D series from Sprague are both surge current tested. Use caution when using ceramic capacitors for input bypassing, because it may cause ringing at the VIN pin. LOWERING OUTPUT RIPPLE When using the adjustable parts, one can achieve lower output ripple voltage by shorting a resistor internal to the LM2825. However, if this resistor is shorted, a feed forward capacitor must be used to keep the regulator stable. For this reason, this resistor must be left open on all of the fixed output voltage versions or instability will result. See the feed forward capacitor selection below. Shorting the internal resistor is accomplished by shorting pins 8 and 9 on the LM2825, and will typically reduce output ripple by 25 to 33%. FEED FORWARD CAPACITOR SELECTION (CFF) When using an adjustable part and pins 8 and 9 are shorted to reduce output ripple, a feed forward capacitor is required. This capacitor is typically between 680 pF and 2700 pF. The table of Figure 4 shows the value for CFF for a given output voltage and feedback resistor R2 (R1 = 1 kΩ).
FIGURE 4. CFF Selection Table SHUTDOWN The circuit shown in Figure 10 shows 2 circuits for the Shutdown/Soft-start feature using different logic signals for shutdown and using a 0.1 µF Soft-start capacitor. THERMAL CONSIDERATIONS The LM2825 is available in a 24-pin through hole DIP. The package is molded plastic with a copper lead frame. When the package is soldered to the PC board, the copper and the board are the heat sink for the LM2825.
FIGURE 5. Usage of the Soft-start Capacitor
OUTPUT CURRENT DERATING FOR TJ = −40˚C to −25˚C AND TJ = −25˚C to 0˚C At the lower temperature extremes, the switch current limit drops off sharply. As a result, a lower output current is available in this temperature range. See Figure 6 and Figure 7 for the typical available output current at these temperature ranges.
FIGURE 6. LM2825 Output Current Derating for TJ = −40˚C to −25˚C
FIGURE 7. LM2825 Output Current Derating for TJ = −25˚C to 0˚C
OUTPUT CURRENT DERATING FOR TA = 0˚C to 70˚C Due to the limited switch current, the LM2825 cannot supply the full one ampere output current over the entire input and output voltage range. Figure 8 shows the typical available output current for any input and output voltage combination. This applies for all output voltage versions.
FIGURE 8. LM2825 Output Current Derating for TA = 0˚C to 70˚C OUTPUT CURRENT DERATING FOR TA = 70˚C to 85˚C At high these high ambient temperatures, the LM2825 cannot supply the full one ampere over the entire input and output voltage range. This is due to thermal reasons and Figure 9 shows the typical available output current for any input and output voltage combination. This applies for all output voltage versions.
FIGURE 9. LM2825 Output Current Derating for TA = 70˚C to 85˚C
FIGURE 10. Typical Circuits Using Shutdown /Soft-start Features TYPICAL THROUGH HOLE PC BOARD LAYOUT (2X SIZE), SINGLE SIDED, THROUGH HOLE PLATED
Note: Holes are not shown. “No Connect Pins” are connected to copper pads for thermal reasons only and must remain electrically isolated.
FIGURE 11. 2X Printed Circuit Board Layout
LM2825 Integrated Power Supply 1A DC-DC Converter
inches (millimeters) unless otherwise noted
24-Lead (0.600″ Wide) Molded Dual-In-Line Package Order Number LM2825N-3.3, LM2825N-5.0, LM2825N12, LM2825N-ADJ or LM2825HN-ADJ NS Package Number NA24F
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