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1.0A Step-Down Switching Regulator
TC2575 TC2575
1.0A Step-Down Switching Regulator
FEATURES
s s s s s s s s s s 3.3V, 5.0V, 12V, and Adjustable Output Versions Adjustable Version Output Voltage Range of 1.23V to 37V 4% Max. Over Line and Load Conditions Guaranteed 1.0 A Output Current Wide Input Voltage Range; 4.75V to 40V Requires Only 4 External Components 52kHz Fixed Frequency Internal Oscillator TTL Shutdown Capability, Low Power Standby Mode High Efficiency Uses Readily Available Standard Inductors Thermal Shutdown and Current Limit Protection The TC2575 series of regulators are monolithic integrated circuits ideally suited for easy and convenient design of a step-down switching regulator (buck converter). All circuits of this series are capable of driving a 1.0A load with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5.0V, 12V, and an adjustable output version. These regulators were designed to minimize the number of external components to simplify the power supply design. Standard series of inductors optimized for use with the TC2575 are offered by several different inductor manufacturers. Since the TC2575 converter is a switch-mode power supply, its efficiency is significantly higher in comparison with popular three-terminal linear regulators, especially with higher input voltages. In many cases, the power dissipated is so low, that no heatsinking is required or its size can be reduced dramatically. The TC2575 features include a guaranteed 4% tolerance on output voltage within specified input voltages and output load conditions, and 10% on the oscillator frequency (2% over 0C to +125C). External shutdown is included, featuring 80A (typical) standby current. The output switch includes cycle-by-cycle current limiting, as well as thermal shutdown for full protection under fault conditions.
APPLICATIONS
s s s s s s Simple and High-Efficiency Step-Down (Buck) Regulator Efficient Pre-Regulator for Linear Regulators On-Card Switching Regulators Positive to Negative Converters (Buck-Boost) Negative Step-Up Converters Power Supply for Battery Chargers
GENERAL DESCRIPTION
PIN CONFIGURATIONS 5-Pin TO-220
ORDERING INFORMATION
Part Number TC2575-3.3VAT TC2575-5.0VAT TC2575-12.0VAT* TC2575VAT** Package 5-Pin TO-220 5-Pin TO-220 5-Pin TO-220 5-Pin TO-220 Temperature Range -40 to +125C -40 to +125C -40 to +125C -40 to +125C
TC2575
Note: * Contact factory for availability ** ADJ = 1.23 To 37V.
12345
TC2575-1 3/13/00
TelCom Semiconductor reserves the right to make changes in the circuitry and specifications of its devices. 1
OUTPUT GND FEEDBACK ON/OFF
VIN
1.0A Step-Down Switching Regulator
TC2575
ABSOLUTE MAXIMUM RATINGS*
Maximum Supply Voltage ................................ VIN = 45V ON/OFF Pin Input Voltage ..................... -0.3V V +VIN Output Voltage to Ground (Steady State) ............... -1.0 V Max Power Dissipation(TO-220) ......... (Internally Limited) Thermal Resistance, Junction-to-Ambient ..... 65C/W Thermal Resistance, Junction-to-Case ........ 5.0C/W Storage Temperature Range ................. -65C to +150C Minimum ESD Rating ............................................. 3.0 kV (Human Body Model: C = 100pF, R = 1.5k) Lead Temperature (Soldering, 10 seconds) .......... 260 C Maximum Junction Temperature............................. 150C Operating Junction Temperature Range .... -40 to +125*C Supply Voltage ............................................................40V
*This is a stress rating only, and functional operation of the device at these or any other conditions beyond those indicated in the operation section of the specifications is not implied. Exposure to absolute maximum ratings conditions for extended periods of time may affect device reliability.
ELECTRICAL CHARACTERISTICS: (Unless otherwise specified, VIN = 12V for the 3.3V, 5.0V, and Adjustable version,VIN = 25V for the 12V version. ILOAD = 200mA. For typical values TJ = 25C, for min/max values TJ is the operating junction temperature range that applies (Note 2), unless otherwise noted.
Symbol
VOUT
Parameter
Output Voltage
Test Conditions
VIN = 12V, ILOAD = 0.2A, TJ = 25C 4.75V VIN 40V, 0.2A ILOAD 1.0A TJ = 25C TJ = -40C to +125 VIN = 12V, ILOAD = 1.0A VIN = 12V, ILOAD = 0.2A, TJ = 25C 8.0V VIN 40V, 0.2A ILOAD 1.0A TJ = 25C TJ = -40C to +125C VIN = 12V, ILOAD = 1.0 A VIN = 25V, ILOAD = 0.2A, TJ = 25C 15V VIN 40V, 0.2A ILOAD 1.0A TJ = 25C TJ = -40C to +125C VIN = 15V, ILOAD = 1.0 A VIN = 12V, ILOAD = 0.2A, VOUT = 5.0V, TJ = 25C 8.0V VIN 40V, 0.2A ILOAD 1.0A VOUT = 5.0V TJ = 25C TJ = -40C to +125C VIN = 12V, ILOAD = 1.0A, VOUT = 5.0V
Min
3.234 3.168 3.135 -- 4.9 4.8 4.75 -- 11.76 11.52 11.4 -- 1.217
Typ
3.3 3.3 -- 75 5.0 5.0 -- 77 12 12 -- 88 1.23
Max
3.366 3.432 3.465 -- 5.1 5.2 5.25 -- 12.24 12.48 12.6 -- 1.243
Units
V
TC2575-3.3 [(Note 1) Test Circuit Figure 2]
VOUT
Efficiency Output Voltage
% V
TC2575-5 [(Note 1)Test Circuit Figure 2]
VOUT
Efficiency Output Voltage
% V
TC2575-12 [(Note 1) Test Circuit Figure 2]
VFB VFB
Efficiency Feedback Voltage Feedback Voltage
% V
TC2575-Adjustable Version [(Note 1) Test Circuit Figure 2]
Efficiency
1.193 1.18 --
1.23 -- 77
1.267 1.28 --
%
NOTES: 1. External components such as the catch diode, inductor, input and output capacitors can affect the switching regulator system performance. When the TC2575 is used as shown in the Figure 2 test circuit, the system performance will be as shown in the system parameters section of the Electrical Characteristics. 2. Tested junction temperature range for the TC2575: TLOW = -40C THIGH = +125C
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1.0A Step-Down Switching Regulator
TC2575
ELECTRICAL CHARACTERISTICS: (Unless otherwise specified, VIN = 12V for the 3.3V, 5.0V, and Adjustable
version,VIN = 25V for the 12V version. ILOAD = 200mA. For typical values TJ = 25C, for min/max values TJ is the operating junction temperature range that applies (Note 2), unless otherwise noted. Symbol
Ib
Parameter
Feedback Bias Current
Test Conditions
Min
Typ
Max
Units
nA
TC2575-ALL OUTPUT VOLTAGE VERSIONS
VOUT = 5.0V (Adjustable Version Only) TJ = 25C TJ = -40C to +125C Oscillator Frequency (Note 3) TJ = 25C TJ = 0 to +125C TJ = -40 to +125C Saturation Voltage IOUT = 1.0A, (Note 4) TJ = 25C TJ = -40 to +125C Max Duty Cycle ("on") [Note 5] Current Limit Peak Current (Notes 3 and 4) TJ = 25C TJ = -40 to +125C Output Leakage Current (Notes 6 and 7), TJ = 25C Output = 0 V Output = - 1.0 V Quiescent Current (Note 6) TJ = 25C TJ = -40 to +125C Standby Quiescent Current, ON/OFF Pin = 5.0 V ("off") TJ = 25C TJ = -40 to +125C ON/OFF Pin Logic Input Level (Test Figure 2) VOUT = 0V TJ = 25C TJ = -40 to +125C Nominal Output Voltage VOUT = Nominal Output Voltage TJ = 25C TJ = -40 to +125C ON/OFF Pin Input Current (Test Figure 2) ON/OFF Pin = 5.0V ("off"), TJ = 25C ON/OFF Pin Input Current ON/OFF Pin = 0V ("on"), TJ = 25C -- -- -- 47 42 -- -- 94 1.7 1.4 -- -- -- -- -- -- 25 -- 52 -- -- 1.0 -- 98 2.3 -- 0.8 6.0 5.0 -- 80 -- 100 200 -- 58 63 1.2 1.3 -- 3.0 3.2 mA 2.0 20 mA 9.0 11 A 200 400 V 2.2 2.4 -- -- -- -- 1.4 -- 1.2 -- 15 0 -- -- V 1.0 0.8 A 30 5.0 A
fOSC
kHz
VSAT
V
DC ICL
% A
IL
IQ
ISTBY
VIH
VIL
IIH
IIL
NOTES: 3. The oscillator frequency reduces to approximately 18kHz in the event of an output short or an overload which causes the regulated output voltage to drop approximately 40% from the nominal output voltage. This self protection feature lowers the average power dissipation of the IC by lowering the minimum duty cycle from 5% down to approximately 2%. 4. Output (Pin 2) sourcing current. No diode, inductor or capacitor connected to the output pin. 5. Feedback (Pin 4) removed from output and connected to 0V. 6. Feedback (Pin 4) removed from output and connected to +12V for the Adjustable, 3.3V, and 5.0V versions, and 25V for the 12V, to force the output transistor "OFF". 7. VIN = 40 V.
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TC2575
PIN DESCRIPTION
Pin No. 5-Pin TO-220
1
Symbol
VIN
Description
This pin is the positive input supply for the TC2575 step-down switching regulator. In order to minimize voltage transients and to supply the switching currents needed by the regulator, a suitable input bypass capacitor must be present (CIN in Figure 1). This is the emitter of the internal switch. The saturation voltage VSAT of this output switch is typically 1.0V. It should be kept in mind that the PCB area connected to this pin should be kept to a minimum in order to minimize coupling to sensitive circuitry. Circuit ground pin. See the information about the printed circuit boad layout. This pin senses regulated output voltage to complete the feedback loop. The signal is divided by the internal resistor divider network R2, R1 and applied to the non-inverting input of the internal error amplifier. In the adjustable version of the TC2575 switching regulator this pin is the direct input of the error amplifier and the resistor network R2, R1 is connected externally to allow programming of the output voltage. It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total input supply current to approximately 80A. The threshold voltage is typically 1.4V. Applying a voltage above this value (up to +VIN) shuts the regulator off. If the voltage applied to this pin is lower than 1.4V or if this pin is left open, the regulator will be in the "on" condition.
2
Output
3 4
GND Feedback
5
ON/OFF
REPRESENTATIVE BLOCK DIAGRAM AND TYPICAL APPLICATION
+VIN
Unregulated DC Input CIN
+
1 TC2575 4
3.1V Internal Regulator
ON/OFF ON/OFF 5
Output Voltage Versions Fixed gain Error Amplifier Current Limit Comparator
R2 ()
Feedback R2
+ -
Driver
+
R1 1.0k
-
Freq. Shift 18kHz 1.235V Band-Gap Reference
+ -
Latch
3.3V 1.7k 5.0V 3.1k 12V 8.84k 15V 11.3k For Adjustable version R1 = open, R2 = 0 Output 1.0 Amp Switch 2 GND 3 L1
Regulated Output VOUT
D1
+
COUT
Load
52kHz Oscillator
Reset
Thermal Shutdown
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1.0A Step-Down Switching Regulator
TC2575
Feedback 7.0 - 40V Unregulated DC Input +VIN CIN 100F 4 TC2575 3 GND Output 2 5 ON/OFF L1 330H 5.0V Regulated Output 1.0A Load D1 1N5819 COUT 330F
+
1
Figure 1. Block Diagram and Typical Application: Fixed Output Voltages
5.0 Output Voltage Versions Feedback VIN 1 VIN Unregulated DC Input 8.0 - 40V + CIN 100F/50V 3 TC2575 (5V) GND 5 4 Output 2 ON/OFF L1 330H COUT + D1 330F/16V IN5819 VOUT Regulated Output
Load
Adjustable Output Voltage Versions Feedback VIN 1 Unregulated DC Input 8.0 - 40V + 3 4 TC2575 Adjustable GND 5 Output 2 ON/OFF D1 IN5819 L1 330H VOUT Regulated Output + CIN 330F/ 16V R2 Load R1
CIN 100F/50V
VOUT = VREF
R2 (1 + R1) R1= R2 (VOUT - 1) VREF Where VREF = 1.23V, R1 between 1.0k and 5.0k Figure 2. Typical Test Circuit
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1.0A Step-Down Switching Regulator
TC2575
PCB LAYOUT GUIDELINES
As in any switching regulator, the layout of the printed circuit board is very important. Rapidly switching currents associated with wiring inductance, stray capacitance and parasitic inductance of the printed circuit board traces can generate voltage transients which can generate electromagnetic interferences (EMI) and affect the desired operation. As indicated in the Figure 2, to minimize inductance and ground loops, the length of the leads indicated by heavy lines should be kept as short as possible. For best results, single-point grounding (as indicated) or ground plane construction should be used. On the other hand, the PCB area connected to the Pin 2 (emitter of the internal switch) of the TC2575 should be kept to a minimum in order to minimize coupling to sensitive circuitry. Another sensitive part of the circuit is the feedback. It is important to keep the sensitive feedback wiring short. To assure this, physically locate the programming resistors near to the regulator, when using the adjustable version of the TC2575 regulator. The next period is the "off" period of the power switch. When the power switch turns off, the voltage across the inductor reverses its polarity and is clamped at one diode voltage drop below ground by the catch diode. Current now flows through the catch diode thus maintaining the load current loop. This removes the stored energy from the inductor. The inductor current during this time is: (VOUT - VD ) tOFF L This period ends when the power switch is once again turned on. Regulation of the converter is accomplished by varying the duty cycle of the power switch. It is possible to describe the duty cycle as follows: IL (OFF) = d = tON , where T is the period of switching. T For the buck converter with ideal components, the duty cycle can also be described as: d = VOUT VIN Figure 4 shows the buck converter idealized waveforms of the catch diode voltage and the inductor current.
VON (SW)
DESIGN PROCEDURE Buck Converter Basics
The TC2575 is a "Buck" or Step-Down Converter which is the most elementary forward-mode converter. Its basic schematic can be seen in Figure 3. The operation of this regulator topology has two distinct time periods. The first one occurs when the series switch is on, the input voltage is connected to the input of the inductor. The output of the inductor is the output voltage, and the rectifier (or catch diode) is reverse biased. During this period, since there is a constant voltage source connected across the inductor, the inductor current begins to linearly ramp upwards, as described by the following equation: (VIN - VOUT ) tON L During this "on" period, energy is stored within the core material in the form of magnetic flux. If the inductor is properly designed, there is sufficient energy stored to carry the requirements of the load during the "off" period. IL (ON) =
Power Switch + VIN - D1 COUT+ RLOAD L VOUT
Diode Voltage
Power Switch Off
Power Switch On
Power Switch Off
Power Switch On
Time
Inductor Current
VD/(FWD) IPK ILOAD (AV) IMIN Diode Power Switch Diode Power Switch Time
Figure 4. Buck Converter Idealized Waveforms
Figure 3. Basic Buck Converter
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1.0A Step-Down Switching Regulator
TC2575
Procedure (Fixed Output Voltage Version)
In order to simplify the switching regulator design, a step-by-step design procedure and some examples are provided. Procedure
Given Parameters: VOUT = Regulated Output Voltage (3.3V, 5.0V or 12V) VIN(max) = Maximum DC Input Voltage ILOAD(max) = Maximum Load Current 1. Controller IC Selection According to the required input voltage, output voltage and current select the appropriate type of the controller IC output voltage version. 2. Input Capacitor Selection (CIN ) To prevent large voltage transients from appearing at the input and for stable operation of the converter, an aluminum or tantalum electrolytic bypass capacitor is needed between the input pin +VIN and ground pin GND. This capacitor should be located close to the IC using short leads. This capacitor should have a low ESR (Equivalent Series Resistance) value. 3. Catch Diode Selection (D1) A. Since the diode maximum peak current exceeds the regulator maximum load current, the catch diode current rating must be at least 1.2 times greater than the maximum load current. For a robust design the diode should have a current rating equal to the maximum current limit of the TC2575 to be able to withstand a continuous output short. B. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. 4. Inductor Selection (L1) A. According to the required working conditions, select the correct inductor value using the selection guide from Figures 32 to 36. B. From the appropriate inductor selection guide, identify the inductance region intersected by the Maximum Input Voltage line and the Maximum Load Current line. Each region is identified by an inductance value and an inductor code. C. Select an appropriate inductor from the several different manufacturers part numbers listed in Table 1 or Table 2 When using Table 2 for selecting the right inductor, the designer must realize that the inductor current rating must be higher than the maximum peak current flowing through the inductor. This maximum peak current can be calculated as follows: 2L where tON is the "on" time of the power switch and tON = VOUT 1.0
x
Example
Given Parameters: VOUT = 5.0V VIN (max) = 20V ILOAD (max) = 0.8A 1. Controller IC Selection According to the required input voltage, output voltage, current polarity and current value, use the TC2575 (5V) controller IC. 2. Input Capacitor Selection (CIN ) A 47F, 25V aluminium electrolytic capacitor located near to the input and ground pins provides sufficient bypassing.
3. Catch Diode Selection (D1) A. For this example the current rating of the diode is 1.0A
B. Use a 30V 1N5818 Schottky diode, or any of the suggested fast recovery diodes shown in Table 4. 4. Inductor Selection (L1) A. Use the inductor selection guide shown in Figure 32 to 36. B. From the selection guide, the inductance area intersected by the 20V line and 0.8A line is L300.
C. Inductor value required is 300H. From Table 1, or Table 2, choose an inductor from any of the listed manufacturers.
IP(max) = ILOAD (max)+
(VIN - VOUT ) tON
VIN
fOSC
For additional information about the inductor, see the inductor section in the "EXTERNAL COMPONENTS" section of this data sheet.
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1.0A Step-Down Switching Regulator
TC2575
Procedure (Fixed Output Voltage Version) (Continued)
In order to simplify the switching regulator design, a step-by-step design procedure and examples are provided. Procedure
5. Output Capacitor Selection (COUT) A. Since the TC2575 is a forward-mode switching regulator with voltage mode control, its open loop 2-pole-2-zero frequency characteristic has the dominant pole-pair determined by the output capacitor and inductor values. For stable operation and an acceptable ripple voltage, (approximately 1% of the output voltage) a value between 100F and 470F is recommended. B. Due to the fact that the higher voltage electrolytic capacitors generally have lower ESR (Equivalent Series Resistance) numbers, the output capacitor's voltage rating should be at least 1.5 times greater than the output voltage. For a 5.0V regulator, a rating at least 8.0V is appropriate, and a 10Vor 16V rating is recommended.
Example
5. Output Capacitor Selection (COUT ) A. COUT = 100F to 470F standard aluminium electrolytic.
B. Capacitor voltage rating = 16V.
Procedure (Adjustable Output Version: TC2575-ADJ)
Procedure
Given Parameters: VOUT = Regulated Output Voltage VIN (max) = Maximum DC Input Voltage ILOAD (max) = Maximum Load Current 1. Programming Output Voltage To select the right programming resistor R1 and R2 value (see Figure 2) use the following formula: VOUT = VREF Given Parameters: VOUT = 8.0V VIN (max) = 12V ILOAD (max) = 1.0V 1. Programming Output Voltage (selecting R1 and R2) Select R1 and R2 R2 VOUT = 1.23 + Select R1 = 1.8k R1
Example
(1.0
)
(1.0 + R2 ) where V R1
REF
= 1.23V R2 = R1
V (V
OUT
- 1.0) = 1.08k
REF
8.0V ( 1.23V
- 1)
Resistor R1 can be between 1.0k and 5.0k. (For best temperature coefficient and stability with time, use 1% metal film resitors). VOUT R2 = R1 - 1) VREF
R1 = 9.91k, choose a 9.88k metal film resistor.
(
2. Input Capacitor Selection (CIN ) To prevent large voltage transients from appearing at the input and for stable operation of the converter, an aluminium or tantalum electrolytic bypass capacitor is needed between the input pin +VIN and ground pin GND. This capacitor should be located close to the IC using short leads. This capacitor should have a low ESR (Equivalent Series Resistance) value. For additional information see input capacitor section in the "EXTERNAL COMPONENTS" section of this data sheet.
2. Input Capacitor Selection (CIN ) A 100F, aluminium electrolytic capacitor located near the input and ground pin provides sufficient bypassing.
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1.0A Step-Down Switching Regulator
TC2575
Procedure (Adjustable Output Version: TC2575-ADJ) (Continued)
Procedure
3. Catch Diode Selection (D1) A. Since the diode maximum peak current exceeds the regulator maximum load current the catch diode current rating must be at least 1.2 times greater than the maximum load current. For a robust design, the diode should have a current rating equal to the maximum current limit of the TC2575 to be able to with stand a continuous output short. B. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. 4. Inductor Selection (L1) A. Use the following formula to calculate the inductor Volt x microsecond [V x s] constant: E x T = ( VIN - VOUT) VOUT 10 x [V x sec] VIN F[Hz]
6
Example
3. Catch Diode Selection (D1) A. For this example, a 3.0A current rating is adequate.
B. Use a 20V IN5820 or MBR320 Schottky diode or any suggested fast recovery diodes in Table 4. 4. Inductor Selection (L1) A. Calculate E x T [V x sec] constant: E x T = ( 12 - 8.0) x 8.0 1000 x = 51[V x sec] 12 52
B. Match the calculated E x T value with the corresponding number on the vertical axis of the Inductor Value Selection Guide shown in Figure 37. This E x T constant is a measure of the energy handling capability of an inductor and is dependent upon the type of core, the core area, the number of turns, and the duty cycle. C. Next step is to identify the inductance region intersected by the E x T value and the maximum load current value on the horizontal axis shown in Figure 35. D. From the inductor code, identify the inductor value. Then select an appropriate inductor from Table 1 or Table 2. The inductor chosen must be rated for a switching frequency of 52kHz and for a current rating of 1.15 x ILOAD . The inductor current rating can also be determined by calculating the inductor peak current: IP (max) = ILOAD(max) + (VIN - VOUT) tON 2L
B. E x T = 51 [V x sec]
C. ILOAD(max) = 1.0A Inductance Region = L220 D. Proper inductor value = 220H Choose the inductor from Table 1 or Table 2
where tON is the "on" time of the power switch and
tON = (VOUT 1.0 )
x
VIN
fOSC
For additional information about the inductor, see the inductor section in the "External Components" section of this data sheet.
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TC2575
Procedure (Adjustable Output Version: TC2575-ADJ) (Continued)
Procedure
5. Output Capacitor Selection (COUT ) A. Since the TC2575 is a forward-mode switching regulator with voltage mode control, its open loop 2-pole-1-zero frequency characteristic has the dominant pole-pair determined by the output capacitor and inductor values. For stable operation, the capacitor must satisfy the following requirement: COUT 7.785 [F] VOUT x L [F] VIN(max)
Example
5. Output Capacitor Selection (COUT ) A. 12 COUT 7.785 = 53F 8 x 220 To achieve an acceptable ripple voltage, select COUT 100F electrolytic capacitor.
B. Capacitor values between 10F and 2000F will satisfy the loop requirements for stable operation. To achieve an acceptable output ripple voltage and transient response, the output capacitor may need to be several times larger than the above formula yields. C. Due to the fact that the higher voltage electrolytic capacitors generally have lower ESR (Equivalent Series Resistance) numbers, the output capacitor's voltage rating should be at least 1.5 times greater than the output voltage. For a 5.0V regulator, a rating of at least 8.0V is appropriate, and a 10V or 16V rating is recommended.
Table 1. Inductor Selection Guide Inductor Code L100 L150 L220 L330 L470 L680 H150 H220 H330 H470 H680 H1000 H1500 H2200 Inductor Value 100H 150H 220H 330H 470H 680H 150H 220H 330H 470H 680H 1000H 1500H 2200H Pulse Eng PE-92108 PE-53113 PE-52626 PE-52627 PE-53114 PE-52629 PE-53115 PE-53116 PE-53117 PE-53118 PE-53119 PE-53120 PE-53121 PE-53122 Renco RL2444 RL1954 RL1953 RL1952 RL1951 RL1950 RL2445 RL2446 RL2447 RL1961 RL1960 RL1959 RL1958 RL2448 AIE 415-0930 415-0953 415-0922 415-0926 415-0927 415-0928 415-0936 430-0636 430-0635 430-0634 415-0935 415-0934 415-0933 415-0945 Tech 39 77 308 BV 77 358 BV 77 408 BV 77 458 BV - 77 508 BV 77 368 BV 77 410 BV 77 460 BV - 77 510 BV 77 558 BV - 77 610 BV
Note: *Contact Manufacturer
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TC2575
Table 2. Inductor Selection Guide Inductance
(H) 68
Current
(A) 0.32 0.58 0.99 1.78 0.48 0.82 1.47 0.39 0.66 1.20 0.32 0.55 1.00 0.42 0.80
Schott
THT 67143940 67143990 67144070 67144140 67143980 67144060 67144130 - 67144050 67144120 67143960 67144040 67144110 67144030 67144100 SMT 67144310 67144360 67144450 67144520 67144350 67144440 67144510 67144340 67144430 67144500 67144330 67144420 67144490 67144410 67144480
Renco
THT RL-1284-68-43 RL-5470-6 RL-5471-5 RL-5471-5 RL-5470-5 RL-5471-4 RL-5471-4 RL-5470-4 RL-5471-3 RL-5471-3 RL-5470-3 RL-5471-2 RL-5471-2 RL-5471-1 RL-5471-1 SMT RL1500-68 RL1500-68 RL1500-68 - RL1500-100 RL1500-100 - RL1500-150 RL1500-150 - RL1500-220 RL1500-220 - RL1500-330 -
Pulse Engineering
THT PE-53804 PE-53812 PE-53821 PE-53830 PE-53811 PE-53820 PE-53829 PE-53810 PE-53819 PE-53828 PE-53809 PE-53818 PE-53827 PE-53817 PE-53826 SMT PE-53804-S PE-53812-S PE-53821-S PE-53830-S PE-53811-S PE-53820-S PE-53829-S PE-53810-S PE-53819-S PE-53828-S PE-53809-S PE-53818-S PE-53827-S PE-53817-S PE-53826-S
Coilcraft
SMT DO1608-68 DO3308-683 DO3316-683 DO5022P-683 DO3308-104 DO3316-104 DO5022P-104 DO3308-154 DO3316-154 DO5022P-154 DO3308-224 DO3316-224 DO5022P-224 DO3316-334 DO5022P-334
100
150
220
330
Note: Table 1 and Table 2 of this Indicator Selection Guide shows some examples of different manufacturer products suitable for design with the TC2575.
Table 3. Example of Several Inductor Manufacturers Phone/Fax Numbers Pulse Engineering Inc. Pulse Engineering Inc. Europe Renco Electronics Inc. AIE Magnetics Coilcraft Inc. Coilcraft Inc., Europe Tech 39
Schott Corp.
Phone Fax Phone Fax Phone Fax Phone Fax Phone Fax Phone Fax Phone Fax
Phone Fax
+ 1-619-674-8100 + 1-619-674-8262 + 353 93 24 107 + 353 93 24 459 + 1-516-645-5828 + 1-516-586-5562 + 1-813-347-2181 + 1-708-322-2645 + 1-708-639-1469 + 44 1236 730 595 + 44 1236 730 627 + 33 8425 2626 + 33 8425 2610
+ 1-612-475-1173 + 1-612-475-1786
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TC2575
Table 2. Diode Selection Guide Schottky 1.0A VR 20V SMT SK12 THT 1N5817 SR102 1N5818 SR103 11DQ03 1N5819 SR104 11DQ04 MBR150 SR105 11DQ05 SMT SK32 MBRD320 SK33 MBRD330 3.0A THT 1N5820 MBR320 SR302 1N5821 MBR330 SR30 31DQ03 1N5822 MBR340 SR304 31DQ04 MBR350 SR305 11DQ05 SNT 1.0A THT SMT Ultra-Fast Recovery 3.0A THT
30V
MBRS130LT3 SK13
MURS120T3 MURS120T3 MUR120 11DF1 HER102 MURD320 MUR320 30WF10 MUR420
40V
50V
MBRS140T3 SK14 10BQ040 10MQ040 MBRS150 10BQ050
MBRS340T3 MBRD340 30WQ04 SK34 MBRD350 SK35 30WQ05
10BF10
31DF1 HER302
TC2575-1 3/13/00
12
1.0A Step-Down Switching Regulator
TC2575
EXTERNAL COMPONENTS Input Capacitor (CIN)
The Input Capacitor Should Have a Low ESR For stable operation of the switch mode converter a low ESR (Equivalent Series Resistance) aluminium or solid tantalum bypass capacitor is needed between the input pin and the ground pin, to prevent large voltage transients from appearing at the input. It must be located near the regulator and use short leads. With most electrolytic capacitors, the capacitance value decreases and the ESR increases with lower temperatures. For reliable operation in temperatures below -25C larger values of the input capacitor may be needed. Also paralleling a ceramic or solid tantalum capacitor will increase the regulator stability at cold temperatures. RMS Current Rating of CIN The important parameter of the input capacitor is the RMS current rating. Capacitors that are physically large and have large surface area will typically have higher RMS current ratings. For a given capacitor value, a higher voltage electrolytic capacitor will be physically larger than a lower voltage capacitor, and thus be able to dissipate more heat to the surrounding air, and therefore will have a higher RMS current rating. The consequences of operating an electrolytic capacitor beyond the RMS current rating is a shortened operating life. In order to assure maximum capacitor operating lifetime, the capacitor's RMS ripple current rating should be: IRMS > 1.2 x d x ILOAD where d is the duty cycle, for a buck regulator t V d = ON = OUT T VIN and d = tON IVOUT I = for a buck-boost regulator. T IVOUTI + VIN In most cases, the higher voltage electrolytic capacitors have lower ESR value. Often capacitors with much higher voltage ratings may be needed to provide low ESR values, that are required for low output ripple voltage. The Output Capacitor Requires an ESR Value that has an Upper and Lower Limit As mentioned above, a low ESR value is needed for low output ripple voltage, typically 1% to 2% of the output voltage. But if the selected capacitor's ESR is extremely low (below 0.05 ), there is a possibility of an unstable feedback loop, resulting in oscillation at the output. This situation can occur when a tantalum capacitor, that can have a very low ESR, is used as the only output capacitor. At Low Temperatures, Put in Parallel Aluminium Electrolytic Capacitors with Tantalum Capacitors Electrolytic capacitors are not recommended for temperatures below -25C. The ESR rises dramatically at cold temperatures and typically rises 3 times at -25C and as much as 10 times at -40C. Solid tantalum capacitors have much better ESR spec at cold temperatures and are recommended for temperatures below -25C. They can be also used in parallel with aluminium electrolytics. The value of the tantalum capacitor should be about 10% or 20% of the total capacitance. The output capacitor should have at least 50% higher RMS ripple current rating at 52kHz than the peak-to-peak inductor ripple current.
Catch Diode
Locate the Catch Diode Close to the TC2575 The TC2575 is a step-down buck converter, it requires a fast diode to provide a return path for the inductor current when the switch turns off. This diode must be located close to the TC2575 using short leads and short printed circuit traces to avoid EMI problems. Use a Schottky or a Soft Switching Ultra-Fast Recovery Diode Since the rectifier diodes are very significant source of losses within switching power supplies, choosing the rectifier that best fits into the converter design is an important process. Schottky diodes provide the best performance because of their fast switching speed and low forward voltage drop. They provide the best efficiency especially in low output voltage applications (5.0 V and lower). Another choice could be Fast-Recovery, or Ultra-Fast Recovery diodes. It has to be noted, that some types of these diodes with an abrupt turnoff characteristic may cause instability or EMI troubles. A fast-recovery diode with soft recovery characteristics can better fulfill a quality, low noise design requirements.
13
Output Capacitor (COUT) For low output ripple voltage and good stability, low ESR output capacitors are recommended. An output capacitor has two main functions: it filters the output and provides regulator loop stability. The ESR of the output capacitor and the peak-to-peak value of the inductor ripple current are the main factors contributing to the output ripple voltage value. Standard aluminium electrolytics could be adequate for some applications but for quality design, low ESR types are recommended. An aluminium electrolytic capacitor's ESR value is related to many factors, such as the capacitance value, the voltage rating, the physical size and the type of construction.
TC2575-1 3/13/00
1.0A Step-Down Switching Regulator
TC2575
Table 4 provides a list of suitable diodes for the TC2575 regulator. Standard 50/60Hz rectifier diodes, such as the 1N4001 series or 1N5400 series are NOT suitable. Inductor The magnetic components are the cornerstone of all switching power supply designs. The style of the core and the winding technique used in the magnetic component's design have a great influence on the reliability of the overall power supply. Using an improper or poorly designed inductor can cause high voltage spikes generated by the rate of transitions in current within the switching power supply, and the possibility of core saturation can arise during an abnormal operational mode. Voltage spikes can cause the semiconductors to enter avalanche breakdown and the part can instantly fail if enough energy is applied. It can also cause significant RFI (Radio Frequency Interference) and EMI (Electro-Magnetic Interference) problems. Continuous and Discontinuous Mode of Operation. The TC2575 step-down converter can operate in both the continuous and the discontinuous modes of operation. The regulator works in the continuous mode when loads are relatively heavy, the current flows through the inductor continuously and never falls to zero. Under light load conditions, the circuit will be forced to the discontinuous mode when inductor current falls to zero for certain period of time (see Figure 5 and Figure 6). Each mode has distinctively different operating characteristics, which can affect the regulator performance and requirements. In many cases the preferred mode of operation is the continuous mode. It offers greater output power, lower peak currents in the switch, inductor and diode, and can have a lower output ripple voltage. On the other hand it does require larger inductor values to keep the inductor current flowing continuously, especially at low output load currents and/orhigh input voltages. To simplify the inductor selection process, an inductor selection guide for the TC2575 regulator was added to this data sheet (Figures 32 through 36). This guide assumes that the regulator is operating in the continuous mode, and selects an inductor that will allow a peak-to-peak inductor ripple current to be a certain percentage of the maximum design load current. This percentage is allowed to change as different design load currents are selected. For light loads (less than approximately 200mA) it may be desirable to operate the regulator in the discontinuous mode, because the inductor value and size can be kept relatively low. Consequently, the percentage of inductor peak-to-peak current increases. This discontinuous mode of operation is perfectly acceptable for this type of switching converter. Any buck regulator will be forced to enter discontinuous mode if the load current is light enough.
Selecting the Right Inductor Style
Some important considerations when selecting a coretype are core material, cost, the output power of the powersupply, the physical volume the inductor must fit within, and the amount of EMI (Electro-Magnetic Interference) shielding that the core must provide. The inductor selection guide covers different styles of inductors such as pot core, E-core, toroid and bobbin core, as well as different core materials such as ferrites and powdered iron from different manufacturers. For high quality design regulators the toroid core seems to be the best choice. Since the magnetic flux is contained within the core, it generates less EMI, reducing noise problems in sensitive circuits. The least expensive is the bobbin core type, which consists of wire wound on a ferrite rod core.
POWER SWITCH CURRENT (A)
1.0
POWER SWITCH CURRENT (A) INDUCTOR CURRENT (A)
0.1 0
0
INDUCTOR CURRENT (A)
1.0
0.1 0 HORIZONTAL TIME BASE: 5.0sec/DIV
0 HORIZONTAL TIME BASE: 5.0sec/DIV
Figure 5. Continuous Mode Switching Current Waveforms
TC2575-1 3/13/00
Figure 6. Discontinuous Mode Switching Current Waveforms 14
1.0A Step-Down Switching Regulator
TC2575
This type of inductor generates more EMI due to the fact that its core is open, and the magnetic flux is not contained within the core. When multiple switching regulators are located on the same printed circuit board, open core magnetics can cause interference between two or more of the regulator circuits, especially at high currents due to mutual coupling. A toroid, pot core or E-core (closed magnetic structure) should be used in such applications. must be kept short. The importance of quality printed circuit board layout design should also be highlighted.
Voltage spikes caused by switching action of the output switch and the parasitic inductance of the output capacitor
UNFILITERED OUTPUT VOLTAGE VERTICAL RESOLUTION: 20mV/DIV FILITERED OUTPUT VOLTAGE
Do Not Operate an Inductor Beyond its Maximum Rated Current
Exceeding an inductor's maximum current rating may cause the inductor to overheat because of the copper wire losses, or the core may saturate. Core saturation occurs when the flux density is too high and consequently the cross sectional area of the core can no longer support additional lines of magnetic flux. This causes the permeability of the core to drop, the inductance value decreases rapidly and the inductor begins to look mainly resistive. It has only the DC resistance of the winding. This can cause the switch current to rise very rapidly and force the TC2575 internal switch into cycle-bycycle current limit, thus reducing the DC output load current. This can also result in overheating of the inductor and/or the TC2575. Different inductor types have different saturation characteristics, and this should be kept in mind when selecting an inductor.
HORIZONTAL TIME BASE: 10sec/DIV
Figure 7. Output Ripple Voltage Waveforms
Minimizing the Output Ripple
In order to minimize the output ripple voltage it is possible to enlarge the inductance value of the inductor L1 and/or to use a larger value output capacitor. There is also another way to smooth the output by means of an additional LC filter (20H, 100F), that can be added to the output (see Figure 16) to further reduce the amount of output ripple and transients. With such a filter it is possible to reduce the output ripple voltage transients 10 times or more. Figure 7 shows the difference between filtered and unfiltered output waveforms of the regulator shown in Figure 16. The upper waveform is from the normal unfiltered output of the converter, while the lower waveform shows the output ripple voltage filtered by an additional LC filter.
GENERAL RECOMMENDATIONS Output Voltage Ripple and Transients Source of the Output Ripple
Since the TC2575 is a switch mode power supply regulator, its output voltage, if left unfiltered, will contain a sawtooth ripple voltage at the switching frequency. The output ripple voltage value ranges from 0.5% to 3% of the output voltage. It is caused mainly by the inductor sawtooth ripple current multiplied by the ESR of the output capacitor.
Heatsinking and Thermal Considerations
The Through-Hole-Package TO-220 The TC2575 is available in a 5-Pin TO-220 package. There are many applications that require no heatsink to keep the TC2575 junction temperature within the allowed operating range. The TO-220 package can be used without a heatsink for ambient temperatures up to approximately 50C (depending on the output voltage and load current). Higher ambient temperatures require some heat sinking, either to the printed circuit (PC) board or an external heatsink.
Short Voltage Spikes and How to Reduce Them
The regulator output voltage may also contain short voltage spikes at the peaks of the sawtooth waveform (see Figure 7). These voltage spikes are present because of the fast switching action of the output switch, and the parasitic inductance of the output filter capacitor. There are some other important factors such as wiring inductance, stray capacitance, as well as the scope probe used to evaluate these transients, all these contribute to the amplitude of these spikes. To minimize these voltage spikes, low inductance capacitors should be used, and their lead lengths
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1.0A Step-Down Switching Regulator
TC2575
Thermal Analysis and Design
The following procedure must be performed to determine whether or not a heatsink will be required. First determine: 1. PD (max) - maximum regulator power dissipation in the application. 2. TA (max) - maximum ambient temperature in the application. 3. TJ (max) - maximum allowed junction temperature (125C for the TC2575). For a conservative design, the maximum junction temperature should not exceed 110C to assure safe operation. For every additional 10C temperature rise that the junction must withstand, the estimated operating lifetime of the component is halved. 4. JC - package thermal resistance junction-case. 5. JA - package thermal resistance junction- ambient. (Refer to Absolute Maximum Ratings on this data sheet or JC and JA values). The following formula is to calculate the approximate total power dissipated by the TC2575: PD = (VIN x IQ ) + d x ILOAD x VSAT where d is the duty cycle and for buck converter d= tON VOUT = T VIN
12 to 25V Unregulated DC Input CIN 100F /50V Feedback +VIN 1 3 TC2575 (12V) GND 5 ON/OFF 4 Output 2 D1 1N5819 COUT 1800F/ 16V L1 100H
-12V @ 0.35A Regulated Output
Figure 8. Inverting Buck-Boost Regulator Using the TC2575 (12V) Develops -12V @ 0.35A
The dynamic switching losses during turn-on and turn- off can be neglected if a proper type catch diode is used. Packages (Free-Standing) For a free-standing application when no heatsink is used, the junction temperature can be determined by the following expression: TJ = (JA ) (PD ) + TA where (JA )(PD ) represents the junction temperature rise caused by the dissipated power and TA is the maximum ambient temperature.
Some Aspects That can Influence Thermal Design
It should be noted that the package thermal resistance and the junction temperature rise numbers are all approximate, and there are many factors that will affect these numbers, such as PC board size, shape, thickness, physical position, location, board temperature, as well as whether the surrounding air is moving or still. Other factors are trace width, total printed circuit copper area, copper thickness, single- or double-sided, multilayer board, the amount of solder on the board or even color of the traces. The size, quantity and spacing of other components on the board can also influence its effectiveness to dissipate the heat.
IQ (quiescent current) and VSAT can be found in the TC2575 data sheet, VIN is minimum input voltage applied, VOUT is the regulator output voltage, ILOAD is the load current.
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1.0A Step-Down Switching Regulator
TC2575
ADDITIONAL APPLICATIONS Inverting Regulator
An inverting buck-boost regulator using the TC2575 (12V) is shown in Figure 8. This circuit converts a positive input voltage to a negative output voltage with a common ground by bootstrapping the regulators ground to the negative output voltage. By grounding the feedback pin, the regulator senses the inverted output voltage and regulates it. In this example the TC2575 (12V) is used to generate a 12V output. The maximum input voltage in this case cannot exceed 28V because the maximum voltage appearing across the regulator is the absolute sum of the input and output voltages and this must be limited to a maximum of 40V. This circuit configuration is able to deliver approximately 0.35A to the output when the input voltage is 12V or higher. At lighter loads the minimum input voltage required drops to approximately 4.7V, because the buck-boost regulator topology can produce an output voltage that, in its absolute value, is either greater or less than the input voltage. Since the switch currents in this buck-boost configuration are higher than in the standard buck converter topology, the available output current is lower. This type of buck-boost inverting regulator can also require a larger amount of startup input current, even for light loads. This may overload an input power source with a current limit less than 1.5A. Such an amount of input start-up current is needed for at least 2.0msec or more. The actual time depends on the output voltage and size of the output capacitor. Because of the relatively high startup currents required by this inverting regulator topology, the use of a delayed startup or an undervoltage lockout circuit is recommended. Using a delayed startup arrangement, the input capacitor can charge up to a higher voltage before the switch- mode regulator begins to operate. The high input current needed for startup is now partially supplied by the input capacitor CIN. select an inductor with an appropriate current rating, the inductor peak current has to be calculated. The following formula is used to obtain the peak inductor current:
IPEAK ILOAD (VIN - IVOUTI) VIN x tON + VIN 2L1 IVOUTI VIN + IVOUTI x 1.0 , and fOSC = 52kHz. fOSC
where tON
Under normal continuous inductor current operating conditions, the worst case occurs when VIN is minimal. Note that the voltage appearing across the regulator is the absolute sum of the input and output voltage, and must not exceed 40V.
12 to 25V Unregulated DC Input CIN 100F /50V C1 0.1F
Feedback +VIN 1 5 R1 47k TC2575 (12V) ON/OFF R2 47k -12V @ 0.35A Regulated Output 3 GND L1 4 Output 100H 2 D1 1N5819 COUT 1800F/16V
Figure 9. Inverting Buck-Boost Regulator with Delayed Startup
It has been already mentioned above, that in some situations, the delayed startup or the undervoltge lockout features could be very useful. A delayed startup circuit applied to a buck-boost converter is shown in Figure 9. Figure 15 in the "Undervoltage Lockout" section describes an undervoltage lockout feature for the same converter topology.
+VIN +VIN 1 CIN R1 100F 47 k 5.0V 0 On Shutdown Input Off R3 470 R2 47k -VOUT MOC8101
NOTE: This picture does not show the complete circuit.
TC2575
Design Recommendations:
The inverting regulator operates in a different manner than the buck converter and so a different design procedure has to be used to select the inductor L1 or the output capacitor COUT. The output capacitor values must be larger than what is normally required for buck converter designs. Low input voltages or high output currents require a large value output capacitor (in the range of thousands of F). The recommended range of inductor values for the inverting converter design is between 68H and 220 H. To
TC2575-1 3/13/00
5
ON/OFF 3
GND
Figure 10. Inverting Buck-Boost Regulator Shutdown Circuit Using an Optocoupler 17
1.0A Step-Down Switching Regulator
TC2575
With the inverting configuration, the use of the ON/OFF pin requires some level shifting techniques. This is caused by the fact, that the ground pin of the converter IC is no longer at ground. Now, the ON/OFF pin threshold voltage (1.4V approximately) has to be related to the negative output voltage level. There are many different possible shutdown methods, two of them are shown in Figures 10 and 11.
+V 0 On R2 5.6 k +VIN +VIN 1 CIN 100F Q1 2N3906 5 TC2575 Off Shutdown Input
VIN Unregulated DC Input -VIN = -5.0V to -12V L1 150H
4 +VIN 1 CIN 100F/ 50V 3 TC2575 (12V) Feedback Output GND 5 2 ON/OFF D1 1N5819 COUT 1000F/16V
Regulated Output VOUT = -12V
Load Current from 200mA for VIN = -5.2V to 500mA for VIN -7.0V
Figure 12. Negative Boost Regulator
Design Recommendations
ON/OFF 3 R1 12k GND
-VOUT
NOTE: This picture does not show the complete circuit.
Figure 11. Inverting Buck-Boost Regulator Shutdown Circuit Using a PNP Transistor
Negative Boost Regulator
This example is a variation of the buck-boost topology and it is called negative boost regulator. This regulator experiences relatively high switch current, especially at low input voltages. The internal switch current limiting results in lower output load current capability. The circuit in Figure 12 shows the negative boost configuration. The input voltage in this application ranges from -5.0 to -12V and provides a regulated -12V output. If the input voltage is greater than -12V, the output will rise above -12 V accordingly, but will not damage the regulator.
The same design rules as for the previous inverting buck-boost converter can be applied. The output capacitor COUT must be chosen larger than what would be required for a standard buck converter. Low input voltages or high output currents require a large value output capacitor (in the range of thousands of F). The recommended range of inductor values for the negative boost regulator is the same as for inverting converter design. Another important point is that these negative boost converters cannot provide any current limiting load protection in the event of a short in the output so some other means, such as a fuse, may be necessary to provide the load protection.
Delayed Startup
There are some applications, like the inverting regulator already mentioned above, which require a higher amount of start-up current. In such cases, if the input power source is limited, this delayed start-up feature becomes very useful. To provide a time delay between the time when the input voltage is applied and the time when the output voltage comes up, the circuit in Figure 13 can be used. As the input voltage is applied, the capacitor C1 charges up, and the voltage across the resistor R2 falls down. When the voltage on the ON/OFF pin falls below the threshold value 1.4 V, the regulator starts up. Resistor R1 is included to limit the maximum voltage applied to the ON/OFF pin. It reduces the power supply noise sensitivity, and also limits the capacitor C1 discharge current, but its use is not mandatory. When a high 50Hz or 60Hz (100Hz or 120Hz respectively) ripple voltage exists, a long delay time can cause some problems by coupling the ripple into the ON/OFF pin, the regulator could be switched periodically on and off with the line (or double) frequency.
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TC2575-1 3/13/00
1.0A Step-Down Switching Regulator
TC2575
Adjustable Output, Low-Ripple Power Supply
+VIN +VIN 1 C1 0.1 F CIN
100F
LM2575
5
ON/OFF 3
GND
R1 47k
A 1.0A output current capability power supply that features an adjustable output voltage is shown in Figure 16. This regulator delivers 1.0A into 1.2 to 35V output. The input voltage ranges from roughly 8.0 to 40V. In order to achieve a 10 or more times reduction of output ripple, an additional L-C filter is included in this circuit.
R2 47k
+VIN
NOTE: This picture does not show the complete circuit. :
+VIN 1
TC2575 (5V) 5 ON/OFF 3 GND
Figure 13. Delayed Startup Circuitry
R2 15k
R3 68k
CIN 100F
Undervoltage Lockout
Some applications require the regulator to remain off until the input voltage reaches a certain threshold level. Figure 14 shows an undervoltage lockout circuit applied to a buck regulator. A version of this circuit for buck-boost converter is shown in Figure 14. Resistor R3 pulls the ON/OFF pin high and keeps the regulator off until the input voltage reaches a predetermined threshold level, with respect to the ground Pin 3, which is determined by the following expression:
R2 VTH VZ1 + 1.0 + R1
Z1 1N5242B Q1 2N3904 R1 15 k VTH 13V
VOUT = -5.0V
NOTE: This picture does not show the complete circuit Figure 15. Undervoltage Lockout Circuit for Buck-Boost Converter
(
)V
BE
(Q1)
+VIN
+VIN 1
TC2575 (5V)
R2 10k
R3 47k
CIN 100F
5
ON/OFF 3
GND
Z1 1N5242B Q1 2N3904 R1 10k VTH 13V
NOTE: This picture does not show the complete circuit.
Figure 14. Undervoltage Lockout Circuit for Buck Converter
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1.0A Step-Down Switching Regulator
TC2575
Feedback Unregulated DC Input +VIN 1 CIN 100F/50V 3 4 TC2575-ADJ Output GND 5 2 ON/OFF D1 1N5819 COUT 2200F R1 1.1k L1 150H R2 50k C1 100F L2 20H Output Voltage 1.2V to 35V @1.0A
Optional Output Ripple Filter
Figure 16. Adjustable Power Supply with Low Ripple Voltage
The TC2576-ADJ Step-Down Voltage Regulator with 8.0V @ 1.0A Output Power Capability. Typical Application with Through-Hole PC Board Layout Regulated Output Filtered 4 Unregulated DC Input +VIN = +10V to + 40V +VIN 1 3 C1 100F /50V TC2575-ADJ Output 2 GND 5 ON/OFF Feedback VOUT = 8.0V @ 1.0A
L1 330mH R2 10k
L2 25H
Regulated Output Filtered VOUT 2 = 8.0V @ 1.0A
D1 1N5819
C2 330F/16V
C3 100F/16V R1 1.8k
VOUT = VREF +
R2 ( 1.0 + R1)
VREF = 1.23V C1 - 100F, 63V, Aluminum Electrolytic R1 is between 1.0k and 5.0k C2 - 330F, 16V, Aluminum Electrolytic C3 - 100F, 16V, Aluminum Electrolytic D1 - 1.0A, 40V, Schottky Rectifier, 1N5819 L1 - 330H, Tech 39: 77 458 BV, Toroid, Through-Hole, Pin 3 = Start, Pin 7 = Finish L2 - 25H, TDK: SFT52501, Toroid Core, Through-Hole R1 - 1.8k R2 - 10k
Figure 17. Schematic Diagram of the 8.0V at 1.0A Step-Down Converter Using the TC2575-ADJ
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1.0A Step-Down Switching Regulator
TC2575
Gndin C1 L1
U1 TC2575 C2 D1 J1
Gndout C3
L2 +Vin R2 R1 NOTE: ot to scale. N
+Vout2 +Vout1
NOTE: Not to scale . Figure 19. PC Board Copper Side
Figure 18. PC Board Component Side
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1.0A Step-Down Switching Regulator
TC2575
TYPICAL CHARACTERISTICS (Circuit of Figure 2)
Figure 20. Normalized Output Voltage Figure 21. Line Regulation 1.0 0.6
V , OUTPUT VOLTAGE CHANGE (%) OUT
V OUTPUT VOLTAGE CHANGE (%) OUT
0.4 0.2 0
VIN = 20 V ILOAD = 200mA Normalized at TJ = 25C
0.8 0.6 0.4 0.2 0
ILOAD = 200mA TJ = 25C 3.3 V, 5.0 V and Adj
-0.2
-0.4 -0.6 -50
12V
-25
0
25
50
75
100
125
-0.2
0
5.0
10
15
20
25
30
35
40
TJ, JUNCTION TEMPERATURE (C)
VIN INPUT VOLTAGE (V)
Figure 22 Switch Saturation Voltage 1.2 3.0
Figure 23. Current Limit
V SATURATION VOLTAGE (V) SAT
1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0 125C 25C -40C
IO , OUTPUT CURRENT (A)
2.5 2.0 1.5 1.0 0.5 VIN = 25V 0 -50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
-25
0
25
50
75
100
125
SWITCH CURRENT (A)
TJ, JUNCTION TEMPERATURE (C)
Figure 24. Dropout Voltage 2.0
Figure 25. Quiescent Current
INPUT-OUTPUT DIFFERENTIAL (V)
1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 -50 -5 0 25 50 75 ILOAD = 200mA ILOAD = 1.0A
IQ , QUIESCENT CURRENT (mA)
VOUT = 5% RIND = 0.2
20 18 16 14 12 10 8.0 6.0 ILOAD = 200mA ILOAD = 1.0A
VOUT = 5.0V Measured at Ground Pin TJ = 25C
100
125
4.0
0
5.0
10
15
20
25
30
35
40
TJ, JUNCTION TEMPERATURE (C)
VIN INPUT VOLTAGE (V)
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1.0A Step-Down Switching Regulator
TC2575
TYPICAL CHARACTERISTICS (Circuit of Figure 2 Cont.)
Figure 26. Standby Quiescent Current
ISTBY, STANDBY QUIESCENT CURRENT ( A) ISTBY, STANDBY QUIESCENT CURRENT ( A)
Figure 27. Standby Quiescent Current 120 100 80 60 40 20 0 -50 VIN = 12V VON/OFF = 5.0V
120 100 80 60 40 20 0 0
TJ = 25C
5.0
10
15
20
25
30
35
40
-25
0
25
50
75
100
125
VIN , INPUT VOLTAGE (V)
TJ, JUNCTION TEMPERATURE (C)
Figure 28. Oscillator Frequency 2.0 0 -2.0 -4.0 -6.0 -8.0 -10 -0
IFB, FEEDBACK PIN CURRENT (nA) NORMALIZED FREQUENCY (%)
Figure 29. Feedback Pin Current 40 Adjustable Version Only
Vin = 12V Normalized at 25C
20
0
-20
-25
0
25
50
75
100
125
-40 -50
-25
0
25
50
75
100
125
TJ, JUNCTION TEMPERATURE (C)
TJ, JUNCTION TEMPERATURE (C)
ILOAD LOAD CURRENT (A) VOUT OUTPUT VOLTAGE CHANGE (mV)
Figure 30. Switching Waveforms OUTPUT 10 V VOLTAGE (PIN 2) 0 OUTPUT 1.0 A CURRENT (PIN 2) 0 INDUCTOR 1.0 A CURRENT 0.5 A OUTPUT 20 mV RIPPLE /DIV VOLTAGE
Figure 31. Load Transient Response
100 0
-100
1.0 0.5 0 100sec/DIV
5.0 sec/DIV
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1.0A Step-Down Switching Regulator
TC2575
TYPICAL CHARACTERISTICS (Circuit of Figure 2 Cont.)
Figure 32. TC2575 (VOUT = 3.3V) 60 VIN, MAXIMUM INPUT VOLTAGE (V) 20 15 10 8.0 7.0 6.0 VIN, MAXIMUM INPUT VOLTAGE (V) H1000 L680 L470 L330 L220 L150 L100 5.0 60 40 25 20 15 12 10 9.0 L220 8.0 L150 7.0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 H1500 H1000 L680 L470 L330 Figure 33.TC2575 (VOUT = 5.0V)
0.2
0.3
0.4
0.5
0.6
0.8
1.0
IL, MAXIMUM LOAD CURRENT (A)
IL, MAXIMUM LOAD CURRENT (A)
Figure 34. TC2575 (VOUT = 12.0V) 60 VIN, MAXIMUM INPUT VOLTAGE (V) H1000 H680 H470 20 18 17 16 15 14 0.2 L680 L470 L330 L220 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 ET, VOLTAGE TIME (Vsec) 40 30 25 H2200 H1500 200 150 125 100 80 70 60 50 40 30 20 0.2 H2200
Figure 35. TC2575-Adj
H1500 H1000 H680 H470
L680 L470 L330 L220 L150 L100 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. IL, MAXIMUM LOAD CURRENT (A)
IL, MAXIMUM LOAD CURRENT (A)
Note: This inductor Value Selection Guide is applicable for continuous mod
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24
1.0A Step-Down Switching Regulator
TC2575
PACKAGE DIMENSIONS
5-Pin TO-220
.185 (4.70) .165 (4.19) .117 (2.97) .103 (2.62) .415 (10.54) .390 (9.91) .156 (3.96) .140 (3.56) DIA. .055 (1.40) .045 (1.14)
.293 (7.44) .204 (5.18) .613 (15.57) .569 (14.45) 3 - 7.5 5 PLCS.
.590 (14.99) .482 (12.24)
.037 (0.95) .025 (0.64) .025 (0.64) .012 (0.30) .072 (1.83) .062 (1.57) .273 (6.93) .263 (6.68) .115 (2.92) .087 (2.21)
PIN 1
Dimensions: inches (mm)
Sales Offices
TelCom Semiconductor, Inc. 1300 Terra Bella Avenue P.O. Box 7267 Mountain View, CA 94039-7267 TEL: 650-968-9241 FAX: 650-967-1590 E-Mail: liter@telcom-semi.com
TC2575-1 3/13/00
TelCom Semiconductor, GmbH Lochhamer Strasse 13 D-82152 Martinsried Germany TEL: (011) 49 89 895 6500 FAX: (011) 49 89 895 6502 2 25
TelCom Semiconductor H.K. Ltd. 10 Sam Chuk Street, Ground Floor San Po Kong, Kowloon Hong Kong TEL: (011) 852-2350-7380 FAX: (011) 852-2354-9957
Printed in the U.S.A.

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