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Datasheet 2A 150KHZ PWM Buck DC/DC Converter General Description
The TD1509 is a of easy to use adjustable step-down (buck) switch-mode voltage regulator. The device is available in an adjustable output version. It is capable of driving a 2A load with excellent line and load regulation. Requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation, and a fixed-frequency oscillator. The output voltage is guaranteed to 3% tolerance under specified input voltage and output load conditions. The oscillator frequency is guaranteed to 15%. External shutdown is included, featuring typically 50 A standby current. Self protection features include a two stage frequency reducing current limit for the output switch and an over temperature shutdown for complete protection under fault conditions. The TD1509 is available in SOP8 DIP8 package.
TD1509
Features
* * * * * * * * * * * 3,3V,5V and Adjustable output versions Output adjustable from 1.23v to 43V Fixed 150KHz frequency internal oscillator Guaranteed 2A output load current Input voltage range up to 45V Low power standby mode, IQ typically 50 A TTL shutdown capability Excellent line and load regulation High efficiency Thermal shutdown and current limit protection Available in advantaged SOP8 DIP8 package
Applications
* * * * * * * Simple High-efficiency step-down regulator On-card switching regulators Positive to negative converter LCD monitor and LCD TV DVD recorder and PDP TV Battery charger Step-down to 3.3V for microprocessors
Package Types
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SOP8
DIP8
Figure 1. Package Types of TD1509
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter Pin Descriptions TD1509
Pin Assignments
Pin 1 2
Name Vin Output
Description Input supply voltage Switching output Ground
5~8 Gnd SOP8/DIP8 3 4
Feedback Output voltage feedback ON/OFF ON/OFF shutdown Active is "Low" or floating
Ordering Information
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TD1509
X
X
Circuit Type
Output Versions R: Adjustable Output 3: Fixed Output 3.3V 5: Fixed Output 5V
Package P: SOP8 D: DIP8
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter Functional Block Diagram TD1509
Figure 2. Functional Block Diagram of TD1509
Typical Application
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter TD1509
Figure 3. Typical Application of TD1509
Note:In PCB layout. Reserved an area for CFF
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter Absolute Maximum Ratings
Note1: Stresses greater than those listed under Maximum Ratings may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation is not implied. Exposure to absolute maximum rating conditions for extended periods may affect reliability.
TD1509
Parameter Supply Voltage Vin Feedback VFB pin voltage ON/OFF Pin voltage Output pin voltage Output Voltage to Ground (Steady State) Power Dissipation Operating Temperature Range Storage Temperature Lead Temperature (Soldering, 10 sec) ESD(HM) Thermal Resistance-Junction to Ambient(RJA) Thermal Resistance-Junction to Case(RJC)
Value -0.3 to 45 -0.3 to Vin+0.3 -0.3 to Vin+0.3 -0.3 to Vin+0.3 -1 Internally limited -40 to +125 -65 to +150 260 2000 85 45
Unit V V V V V W C C C V C / W C / W
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Electrical Characteristics
Unless otherwise specified, Vin = 12V. Iload = 0.5A, Ta = 25. Symbol Ib IQ ISTBY FOSC VSAT ICL IL IL Parameter Feedback bias current Quiescent current
Standby quiescent current
Conditions VFB=1.3V VFB=12V force driver off ON/OFF=5V, VIN=36V
Min.
Typ. 10 5 50
Max. 50/100 10 100 173 1.3
Uni t nA mA uA KHz V A
Oscillator frequency Saturation voltage Current Limit Output leakage current Output leakage current IOUT=2A Peak Current (VFB=0V) Output=0V (VFB=12V) Output=-1V (VIN=32V)
127
150 1.10 3.8
50 2 30
uA mA
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter
VIL VIH IH IL JC JA TD1509 ADJ ON/OFF pin logic input Threshold voltage
ON/OFF pin input current VLOGIC=0.5V(Regulator ON)
TD1509
1.3 2.0 1.3 5 0.02 10 40 1.193/ 1.180 1.23 89 3.168/3 .135 3.3 76 4.800/4 .750 5.0 85 5.200/ 5.250 3.432/ 3.465 1.267/ 1.280 15 5 0.6 V V uA uA
O
Low (Regulator ON) High (Regulator OFF)
VLOGIC=2.5V(Regulator OFF)
Thermal Resistance Junction to Case Thermal Resistance Junction to Ambient (Note1) Vfb: Output Voltage : Efficiency Vout: Output Voltage : Efficiency Vout: Output Voltage : Efficiency
SOP8/DIP8 SOP8/DIP8 11VVIN 45V, 0.2AILOAD 2A, VOUT for 9V VIN=12V,VOUT=9V,ILOAD=2A 4.75VVIN45V, 0.2AILOAD 2A VIN=12V, ILOAD=2A 7V VIN 45V, 0.2A ILOAD 2A VIN=12V, ILOAD=2A
C/ W C/ W
O
V % V % V %
TD1509 3.3V TD1509 5V
Specifications with boldface type are for full operationg temperature range, the other type are for TJ=25OC. Note1: Thermal resistance with copper area of approximately 3 in2.
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter Typical Performance Characteristics TD1509
Figure 4. Output Voltage vs. Temperature
Figure 5. Switching Frequency vs. Temperature
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Figure 6. Output Saturation Characteristics
Figure 7. Quiescent Current vs. Temperature
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter TD1509
Figure 8. ON/OFF Pin Voltage
Figure 9. ON/OFF Pin Sink Current
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Figure 10. Output Saturation Characteristics
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter Typical Application Circuit
(Adjustable Output Voltage Version)
TD1509
Figure 11. Typical Application of TD1509 For 3.3V 5V Output Capacitor (Cout) Through Hole Electrolytic Surface Mount Tantalum 470uf/25V 330uf/6.3V 560uf/25V 330uf/6.3V
Input Voltage 6V ~ 18V 6V ~ 45V
Inductor (L1) 47uh 68uh
Table 1. TD1509 Series Buck Regulator Design Procedure For 3.3V
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Input Voltage 8V ~ 18V 8V ~ 45V
Inductor (L1) 33uh 47uh
Output Capacitor (Cout) Through Hole Electrolytic Surface Mount Tantalum 330uf/25V 220uf/10V 470uf/25V 330uf/10V
Table 2. TD1509 Series Buck Regulator Design Procedure For 5V
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter TD1509
Figure 12. Typical Application of TD1509 For ADJ
Note:In PCB layout. Reserved an area for CFF
Vout 3.3V 5V 9V 12V
R1 1.6K 3.6K 6.8K 1.5K
R2 2.7K 11K 43K 13K
Cf (Operational) 33nf 10nf 1.5nf 1nf
Table 3. Vout VS. R1, R2, Cf Select Table
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Output Voltage 3.3V 5V 9V 12V
Input Voltage 6V ~ 18V 6V ~36V 8V ~ 18V 8V ~36V 12V ~18V 12V ~36V 15V ~ 18V 15V ~36V
Inductor (L1) 47uh 68uh 33uh 47uh 47uh 47uh 47uh 47uh
Output Capacitor (Cout) Through Hole Electrolytic 470uf/25V 560uf/25V 330uf/25V 470uf/25V 330uf/25V 470uf/25V 220uf/25V 330uf/25V
Table 4. Typical Application Buck Regulator Design Procedure
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter Function Description
Pin Functions +VIN
TD1509
approximate and there are many factors that can affect these temperatures. Higher ambient temperatures require more heat sinking. For the best thermal performance, wide copper traces and generous amounts of printed circuit board copper should be used in the board layout. (Once exception to this is the output (switch) pin, which should not have large areas of copper.) Large areas of copper provide the best transfer of heat (lower thermal resistance) to the surrounding air, and moving air lowers the thermal resistance even further. Package thermal resistance and junction temperature rise numbers are all approximate, and there are many factors that will affect these numbers. Some of these factors include board size, shape, thickness, position, location, and even board temperature. Other factors are, trace width, total printed circuit copper area, copper thickness, single or double-sided, multi-layer board and the amount of solder on the board. The effectiveness of the PC board to dissipate heat also depends on the size, quantity and spacing of other components on the board, as well as whether the surrounding air is still or moving. Furthermore, some of these components such as the catch diode will add heat to the PC board and the heat can vary as the input voltage changes. For the inductor, depending on the physical size, type of core material and the DC resistance, it could either act as a heat sink taking heat away from the board, or it could add heat to the board.
This is the positive input supply for the IC switching regulator. A suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents needed by the regulator
Ground
Circuit ground.
Output
Internal switch. The voltage at this pin switches between (+VIN - VSAT) and approximately - 0.5V, with a duty cycle of approximately VOUT / VIN. To minimize coupling to sensitive circuitry, the PC board copper area connected to this pin should be kept a minimum.
Feedback
Senses the regulated output voltage to complete the feedback loop.
ON/OFF
Allows the switching regulator circuit to be shutdown using logic level signals thus dropping the total input supply current to approximately 50uA. Pulling this pin below a threshold voltage of approximately 1.3V turns the regulator on, and www..com pulling this pin above 1.3V (up to a maximum of 32V) shuts the regulator down. If this shutdown feature is not needed, the ON /OFF pin can be wired to the ground pin or it can be left open, in either case the regulator will be in the ON condition.
Setting the Output Voltage
The output voltage is set using a resistive voltage divider from the output voltage to FB The voltage divider divides the output voltage down by the ratio: VFB = VOUT * R1 / (R1 + R2) Thus the output voltage is: VOUT = 1.235 * (R1 + R2) / R1 R1 can be as high as 100K, but a typical value is 10K. Using that value, R2 is determined by: R2 ~= 8.1 * (VOUT - 1.235) (K)
Thermal Considerations
The TD1509 is available in SOP8/DIP8 package. The SOP8/DIP8 package needs a heat sink under most conditions. The size of the heat sink depends on the input voltage, the output voltage, the load current and the ambient temperature. The TD1509 junction temperature rises above ambient temperature for a 2A load and different input and output voltages. The data for these curves was taken with the TD1509 (SOP8/DIP8 package) operating as a buck-switching regulator in an ambient temperature of 25oC (still air). These temperature rise numbers are all
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Inductor
The inductor is required to supply constant current to the output load while being driven by
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter
the switched input voltage. A larger value inductor results in less ripple current that in turn results in lower output ripple voltage. However, the larger value inductor has a larger physical size, higher series resistance, and/or lower saturation current. Choose an inductor that does not saturate under the worst-case load conditions. A good rule for determining the inductance is to allow the peak-to-peak ripple current in the inductor to be approximately 30% of the maximum load current. Also, make sure that the peak inductor current (the load current plus half the peak-to-peak inductor ripple current) is below the TBDA minimum current limit. The inductance value can be calculated by the equation: L = (VOUT) * (VIN-VOUT) / VIN * f * I Where VOUT is the output voltage, VIN is the input voltage, f is the switching frequency, and I is the peak-to-peak inductor ripple current.
TD1509
Input Capacitor
The input current to the step-down converter is discontinuous, and so a capacitor is required to supply the AC current to the step-down converter while maintaining the DC input voltage. A low ESR capacitor is required to keep the noise at the IC to a minimum. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also suffice. www..com The input capacitor value should be greater than 10F. The capacitor can be electrolytic, tantalum or ceramic. However since it absorbs the input switching current it requires an adequate ripple current rating. Its RMS current rating should be greater than approximately 1/2 of the DC load current. For insuring stable operation should be placed as close to the IC as possible. Alternately a smaller high quality ceramic 0.1F capacitor may be placed closer to the IC and a larger capacitor placed further away. If using this technique, it is recommended that the larger capacitor be a tantalum or electrolytic type. All ceramic capacitors should be places close to the TD1509.
low. The characteristics of the output capacitor also affect the stability of the regulation control system. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance, and so the output voltage ripple is mostly independent of the ESR. The output voltage ripple is estimated to be: VRIPPLE ~= 1.4 * VIN * (fLC/fSW)^2 Where VRIPPLE is the output ripple voltage, VIN is the input voltage, fLC is the resonant frequency of the LC filter, fSW is the switching frequency. In the case of tanatalum or lowESR electrolytic capacitors, the ESR dominates the impedance at the switching frequency, and so the output ripple is calculated as: VRIPPLE ~= I * RESR Where VRIPPLE is the output voltage ripple, I is the inductor ripple current, and RESR is the equivalent series resistance of the output capacitors.
Output Rectifier Diode
The output rectifier diode supplies the current to the inductor when the high-side switch is off. To reduce losses due to the diode forward voltage and recovery times, use a Schottky rectifier. Table 1 provides the Schottky rectifier part numbers based on the maximum input voltage and current rating. Choose a rectifier who's maximum reverse voltage rating is greater than the maximum input voltage, and who's current rating is greater than the maximum load current.
Feedforward Capacitor (CFF)
For output voltages greater than approximately 8V, an additional capacitor is required. The compensation capacitor is typically between 100 pF and 33 nF, and is wired in parallel with the output voltage setting resistor, R2. It provides additional stability for high output voltages, low input-output voltages, and/or very low ESR output capacitors, such as solid tantalum capacitors.
Output Capacitor
The output capacitor is required to maintain the DC output voltage. Low ESR capacitors are preferred to keep the output voltage ripple
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This capacitor type can be ceramic, plastic, silver mica, etc.(Because of the unstable characteristics
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter
of ceramic capacitors made with Z5U material, they are not recommended.) Note:In PCB layout. Reserved an area for CFF.
TD1509
Over Current Protection (OCP)
The cycle by cycle current limit threshold is set between 3.8A and 4A. When the load current reaches the current limit threshold, the cycle by cycle current limit circuit turns off the high side switch immediately to terminate the current duty cycle. The inductor current stops rising. The cycle by cycle current limit protection directly limits inductor peak current. The average inductor current is also limited due to the limitation on peak inductor current. When the cycle by cycle current limit circuit is triggered, the output voltage drops as the duty cycle is decreasing.
Thermal Management and Layout Consideration
In the TD1509 buck regulator circuit, high pulsing current flows through two circuit loops. The first loop starts from the input capacitors, to the VIN pin, to the VOUT pins, to the filter inductor, to the output capacitor and load, and then returns to the input capacitor through ground. Current flows in the first loop when the high side switch is on. The second loop starts from the inductor, to the output capacitors and load, to the GND pin of the TD1509, and to the VOUT pins of the TD1509. Current flows in the second loop when the low side diode is on. In PCB layout, minimizing the two loops area reduces the noise of this circuit and improves www..com efficiency. A ground plane is recommended to connect input capacitor, output capacitor, and GND pin of the TD1509. In the TD1509 buck regulator circuit, the two major power dissipating components are the TD1509 and output inductor. The total power dissipation of converter circuit can be measured
by input power minus output power. Ptotal _loss = V IN x IIN - V O x IO The power dissipation of inductor can be approximately calculated by output current and DCR of inductor. Pinductor _loss= IO 2 x Rinductor x 1.1 The junction to ambient temperature can be got from power dissipation in the TD1509 and thermal impedance from junction to ambient. T (jun-amb) =(Ptotalloss-Pinductorloss)x JA The maximum junction temperature of TD1509 is 145C, which limits the maximum load current capability. Please see the thermal de-rating curves for the maximum load current of the TD1509 under different ambient temperatures. The thermal performance of the TD1509 is trongly affected by the PCB layout. Extra care should be taken by users during the design process to nsure that the IC will operate under the recommended environmental conditions. Several layout tips are listed below for the best electric and thermal performance. 1. Do not use thermal relief connection to the VIN and the GND pin. Pour a maximized copper area to the GND pin and the VIN pin to help thermal dissipation. 2. Input capacitor should be connected to the VIN pin and the GND pin as close as possible. 3. Make the current trace from VOUT pins to L to the GND as short as possible. 4. Pour copper plane on all unused board area and connect it to stable DC nodes, like VIN, GND, or VOUT. 5. Keep sensitive signal traces such as trace connecting FB pin away from the VOUT pins.
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter Package Information
SOP8 Package Outline Dimensions
TD1509
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter Package Information
DIP8 Package Outline Dimensions
TD1509
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Datasheet 2A 150KHZ PWM Buck DC/DC Converter Design Notes TD1509
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