SNVS556C April   2008  – January 2016 LM2738

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Boost Function
      2. 7.3.2 Soft-Start
      3. 7.3.3 Output Overvoltage Protection
      4. 7.3.4 Undervoltage Lockout
      5. 7.3.5 Current Limit
      6. 7.3.6 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Enable Pin and Shutdown Mode
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1  LM2738X Circuit Example 1
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Inductor Selection
          2. 8.2.1.2.2 Input Capacitor
          3. 8.2.1.2.3 Output Capacitor
          4. 8.2.1.2.4 Catch Diode
          5. 8.2.1.2.5 Output Voltage
          6. 8.2.1.2.6 Calculating Efficiency and Junction Temperature
        3. 8.2.1.3 Application Curve
      2. 8.2.2  LM2738X Circuit Example 2
        1. 8.2.2.1 Detailed Design Procedure
        2. 8.2.2.2 Application Curve
      3. 8.2.3  LM2738X Circuit Example 3
        1. 8.2.3.1 Detailed Design Procedure
        2. 8.2.3.2 Application Curve
      4. 8.2.4  LM2738X Circuit Example 4
        1. 8.2.4.1 Detailed Design Procedure
      5. 8.2.5  LM2738X Circuit Example 5
        1. 8.2.5.1 Detailed Design Procedure
      6. 8.2.6  LM2738Y Circuit Example 6
        1. 8.2.6.1 Detailed Design Procedure
        2. 8.2.6.2 Application Curve
      7. 8.2.7  LM2738Y Circuit Example 7
        1. 8.2.7.1 Detailed Design Procedure
        2. 8.2.7.2 Application Curve
      8. 8.2.8  LM2738Y Circuit Example 8
        1. 8.2.8.1 Detailed Design Procedure
        2. 8.2.8.2 Application Curve
      9. 8.2.9  LM2738Y Circuit Example 9
        1. 8.2.9.1 Detailed Design Procedure
        2. 8.2.9.2 Application Curve
      10. 8.2.10 LM2738Y Circuit Example 10
        1. 8.2.10.1 Detailed Design Procedure
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 WSON Package
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
      1. 10.3.1 Silicon Junction Temperature Determination Methods
        1. 10.3.1.1 Method 1
        2. 10.3.1.2 Method 2
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ(パッケージ|ピン)
サーマルパッド・メカニカル・データ

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers must validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LM2738 operates over a wide range of conditions, which is limited by the ON time of the device. Figure 29 shows the recommended operating area for the X version at the full load (1.5 A) and at 25°C ambient temperature. The Y version of the LM2738 operates at a lower frequency, and therefore operates over the entire range of operating voltages.

LM2738 30049187.png Figure 29. LM2738X – 1.6 MHz (25°C, Load = 1.5 A)

8.2 Typical Applications

8.2.1 LM2738X Circuit Example 1

LM2738 30049142.gif Figure 30. LM2738X (1.6 MHz)
VBOOST Derived from VIN
5 V to 1.5 V/1.5 A

8.2.1.1 Design Requirements

The device must be able to operate at any voltage within the Recommended Operating Conditions. The load current must be defined to properly size the inductor, input, and output capacitors. The inductor must be able to support the full expected load current as well as the peak current generated from load transients and start-up.

8.2.1.2 Detailed Design Procedure

Table 1. Bill of Materials for Figure 30

PART ID PART VALUE PART NUMBER MANUFACTURER
U1 1.5-A Buck Regulator LM2738X Texas Instruments
C1, Input Cap 10 µF, 6.3 V, X5R C3216X5ROJ106M TDK
C2, Output Cap 22 µF, 6.3 V, X5R C3216X5ROJ226M TDK
C3, Boost Cap 0.1 uF, 16 V, X7R C1005X7R1C104K TDK
D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba
D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc.
L1 2.2 µH, 1.9 A, MSS5131-222ML Coilcraft
R1 8.87 kΩ, 1% CRCW06038871F Vishay
R2 10.2 kΩ, 1% CRCW06031022F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay

8.2.1.2.1 Inductor Selection

The duty cycle (D) can be approximated quickly using the ratio of output voltage (VO) to input voltage (VIN), using Equation 11:

Equation 11. LM2738 30049138.gif

The catch diode (D1) forward voltage drop and the voltage drop across the internal NMOS switch must be included to calculate a more accurate duty cycle. Calculate D by using Equation 12:

Equation 12. LM2738 30049121.gif

VSW can be approximated by Equation 13:

Equation 13. VSW = IOUT × RDSON

The diode forward drop (VD) can range from 0.3 V to 0.7 V depending on the quality of the diode. The lower the VD, the higher the operating efficiency of the converter. The inductor value determines the output ripple current. Lower inductor values decrease the size of the inductor, but increase the output ripple current. An increase in the inductor value decreases the output ripple current.

One must ensure that the minimum current limit (2 A) is not exceeded, so the peak current in the inductor must be calculated. The peak current (ILPK) in the inductor is calculated by Equation 14 and Equation 15:

Equation 14. ILPK = IOUT + ΔiL
LM2738 30049180.png Figure 31. Inductor Current
Equation 15. LM2738 30049181.gif

In general in Equation 16,

Equation 16. ΔiL = 0.1 × (IOUT) → 0.2 × (IOUT)

If ΔiL = 33.3% of 1.5 A, the peak current in the inductor is 2 A. The minimum specified current limit over all operating conditions is 2 A. One can either reduce ΔiL, or make the engineering judgment that zero margin is safe enough. The typical current limit is 2.9 A.

The LM2738 operates at frequencies allowing the use of ceramic output capacitors without compromising transient response. Ceramic capacitors allow higher inductor ripple without significantly increasing output ripple. See the Output Capacitor section for more details on calculating output voltage ripple. Now that the ripple current is determined, the inductance is calculated by Equation 17:

Equation 17. LM2738 30049182.gif

where

  • LM2738 30049183.gif

When selecting an inductor, make sure that it is capable of supporting the peak output current without saturating. Inductor saturation results in a sudden reduction in inductance and prevents the regulator from operating correctly. Because of the speed of the internal current limit, the peak current of the inductor need only be specified for the required maximum output current. For example, if the designed maximum output current is 1 A and the peak current is 1.25 A, the inductor must be specified with a saturation current limit of > 1.25 A. There is no must specify the saturation or peak current of the inductor at the 2.9-A typical switch current limit. Because of the operating frequency of the LM2738, ferrite based inductors are preferred to minimize core losses. This presents little restriction because of the variety of ferrite-based inductors available. Lastly, inductors with lower series resistance (RDCR) provide better operating efficiency. For recommended inductors see LM2738X Circuit Example 1.

8.2.1.2.2 Input Capacitor

An input capacitor is necessary to ensure that VIN does not drop excessively during switching transients. The primary specifications of the input capacitor are capacitance, voltage, RMS current rating, and equivalent series inductance (ESL). The recommended input capacitance is 10 µF. The input voltage rating is specifically stated by the capacitor manufacturer. Make sure to check any recommended deratings and also verify if there is any significant change in capacitance at the operating input voltage and the operating temperature. The input capacitor maximum RMS input current rating (IRMS-IN) must be greater than Equation 18:

Equation 18. LM2738 30049184.gif

Neglecting inductor ripple simplifies Equation 18 to Equation 19:

Equation 19. LM2738 30049185.gif

Equation 19 shows that maximum RMS capacitor current occurs when D = 0.5. Always calculate the RMS at the point where the duty cycle D is closest to 0.5. The ESL of an input capacitor is usually determined by the effective cross-sectional area of the current path. A large leaded capacitor has high ESL and a 0805 ceramic-chip capacitor has very low ESL. At the operating frequencies of the LM2738, leaded capacitors may have an ESL so large that the resulting impedance (2πfL) is higher than that required to provide stable operation. As a result, surface-mount capacitors are strongly recommended.

Sanyo POSCAP, Tantalum or Niobium, Panasonic SP, and multilayer ceramic capacitors (MLCC) are all good choices for both input and output capacitors and have very low ESL. For MLCCs, TI recommends using X7R or X5R type capacitors due to their tolerance and temperature characteristics. Consult the capacitor manufacturer's data sheets to see how rated capacitance varies over operating conditions.

8.2.1.2.3 Output Capacitor

The output capacitor is selected based upon the desired output ripple and transient response. The initial current of a load transient is provided mainly by the output capacitor. The output ripple of the converter is Equation 20:

Equation 20. LM2738 30049186.gif

When using MLCCs, the equivalent series resistance (ESR) is typically so low that the capacitive ripple may dominate. When this occurs, the output ripple is approximately sinusoidal and 90° phase shifted from the switching action. Given the availability and quality of MLCCs and the expected output voltage of designs using the LM2738, there is really no must review any other capacitor technologies. Another benefit of ceramic capacitors is the ability to bypass high-frequency noise. A certain amount of switching edge noise couples through parasitic capacitances in the inductor to the output. A ceramic capacitor bypasses this noise while a tantalum capacitor does not. Since the output capacitor is one of the two external components that control the stability of the regulator control loop, most applications require a minimum of 22 µF of output capacitance. Capacitance, in general, is often increased when operating at lower duty cycles. Refer to the Circuit Examples for suggested output capacitances of common applications. Like the input capacitor, recommended multilayer ceramic capacitors are X7R or X5R types.

8.2.1.2.4 Catch Diode

The catch diode (D1) conducts during the switch off time. A Schottky diode is recommended for its fast switching times and low forward voltage drop. The catch diode must be chosen so that its current rating is greater than Equation 21:

Equation 21. ID1 = IOUT × (1-D)

The reverse breakdown rating of the diode must be at least the maximum input voltage plus appropriate margin. To improve efficiency, choose a Schottky diode with a low forward-voltage drop.

8.2.1.2.5 Output Voltage

The output voltage is set using Equation 22 and Equation 23 where R2 is connected between the FB pin and GND, and R1 is connected between VO and the FB pin. A good value for R2 is 10 kΩ. When designing a unity gain converter (VO = 0.8 V), R1 must be between 0 Ω and 100 Ω, and R2 must not be loaded.

Equation 22. LM2738 30049141.gif
Equation 23. VREF = 0.80 V

8.2.1.2.6 Calculating Efficiency and Junction Temperature

The complete LM2738 DC-DC converter efficiency can be calculated by Equation 24 or Equation 25:

Equation 24. LM2738 30049164.gif

or,

Equation 25. LM2738 30049165.gif

Calculations for determining the most significant power losses are shown in Equation 26. Other losses totaling less than 2% are not discussed.

Power loss (PLOSS) is the sum of two basic types of losses in the converter: switching and conduction. Conduction losses usually dominate at higher output loads, whereas switching losses remain relatively fixed and dominate at lower output loads. The first step in determining the losses is to calculate the duty cycle (D):

Equation 26. LM2738 30049166.gif

VSW is the voltage drop across the internal NFET when it is on, and is equal to Equation 27:

Equation 27. VSW = IOUT × RDSON

VD is the forward voltage drop across the Schottky catch diode. It can be obtained from the diode manufacturer's data sheet Electrical Characteristics section. If the voltage drop across the inductor (VDCR) is accounted for, the equation becomes Equation 28:

Equation 28. LM2738 30049167.gif

The conduction losses in the free-wheeling Schottky diode are calculated by Equation 29:

Equation 29. PDIODE = VD × IOUT × (1-D)

Often this is the single most significant power loss in the circuit. Care must be taken to choose a Schottky diode that has a low forward-voltage drop.

Another significant external power loss is the conduction loss in the output inductor. The equation can be simplified to Equation 30:

Equation 30. PIND = IOUT2 × RDCR

The LM2738 conduction loss is mainly associated with the internal NFET switch in Equation 31:

Equation 31. LM2738 30049168.gif

If the inductor ripple current is fairly small, the conduction losses can be simplified to Equation 32:

Equation 32. PCOND = IOUT2 × RDSON × D

Switching losses are also associated with the internal NFET switch. They occur during the switch on and off transition periods, where voltages and currents overlap resulting in power loss. The simplest means to determine this loss is to empirically measure the rise and fall times (10% to 90%) of the switch at the switch node.

Switching Power Loss is calculated as follows in Equation 33, Equation 34, and Equation 35:

Equation 33. PSWR = 1/2(VIN × IOUT × FSW × TRISE)
Equation 34. PSWF = 1/2(VIN × IOUT × FSW × TFALL)
Equation 35. PSW = PSWR + PSWF

Another loss is the power required for operation of the internal circuitry in Equation 36:

Equation 36. PQ = IQ × VIN

IQ is the quiescent operating current, and is typically around 1.9 mA for the 0.55-MHz frequency option.

Table 2 lists the power losses for a typical application, and in Equation 37, Equation 38, and Equation 39.

Table 2. Typical Configuration and Power Loss Calculation

PARAMETER VALUE POWER PARAMETER CALCULATED POWER
VIN 12 V
VOUT 3.3 V POUT 4.125 W
IOUT 1.25 A
VD 0.34 V PDIODE 317 mW
FSW 550 kHz
IQ 1.9 mA PQ 22.8 mW
TRISE 8 nS PSWR 33 mW
TFALL 8 nS PSWF 33 mW
RDS(ON) 275 mΩ PCOND 118 mW
INDDCR 70 mΩ PIND 110 mW
D 0.275 PLOSS 634 mW
η 86.7% PINTERNAL 207 mW
Equation 37. ΣPCOND + PSW + PDIODE + PIND + PQ = PLOSS
Equation 38. ΣPCOND + PSWF + PSWR + PQ = PINTERNAL
Equation 39. PINTERNAL = 207 mW

8.2.1.3 Application Curve

LM2738 30049197.png
VOUT = 5 V
Figure 32. Efficiency vs Load Current – X Version

8.2.2 LM2738X Circuit Example 2

LM2738 30049193.png Figure 33. LM2738X (1.6 MHz)
VBOOST Derived from VOUT
12 V to 3.3 V / 1.5 A

8.2.2.1 Detailed Design Procedure

Table 3. Bill of Materials for Figure 33

PART ID PART VALUE PART NUMBER MANUFACTURER
U1 1.5-A Buck Regulator LM2738X Texas Instruments
C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK
C2, Output Cap 33 µF, 6.3 V, X5R C3216X5ROJ336M TDK
C3, Boost Cap 0.1 µF, 16 V, X7R C1005X7R1C104K TDK
D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba
D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc.
L1 5 µH, 2.9 A MSS7341- 502NL Coilcraft
R1 31.6 kΩ, 1% CRCW06033162F Vishay
R2 10 kΩ, 1% CRCW06031002F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay

8.2.2.2 Application Curve

LM2738 30049151.png
VOUT = 3.3 V
Figure 34. Efficiency vs Load Current – X Version

8.2.3 LM2738X Circuit Example 3

LM2738 30049144.gif Figure 35. LM2738X (1.6 MHz)
VBOOST Derived from VSHUNT
18 V to 1.5 V / 1.5 A

8.2.3.1 Detailed Design Procedure

Table 4. Bill of Materials for Figure 35

PART ID PART VALUE PART NUMBER MANUFACTURER
U1 1.5-A Buck Regulator LM2738X Texas Instruments
C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK
C2, Output Cap 47 µF, 6.3 V, X5R C3216X5ROJ476M TDK
C3, Boost Cap 0.1 µF, 16 V, X7R C1005X7R1C104K TDK
C4, Shunt Cap 0.1 µF, 6.3 V, X5R C1005X5R0J104K TDK
D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba
D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc.
D3, Zener Diode 5.1-V 250-Mw SOT-23 BZX84C5V1 Vishay
L1 2.7 µH, 1.76 A VLCF5020T-2R7N1R7 TDK
R1 8.87 kΩ, 1% CRCW06038871F Vishay
R2 10.2 kΩ, 1% CRCW06031022F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay
R4 4.12 kΩ, 1% CRCW06034121F Vishay

8.2.3.2 Application Curve

LM2738 30049199.png
VOUT = 1.5 V
Figure 36. Efficiency vs Load Current – X Version

8.2.4 LM2738X Circuit Example 4

LM2738 30049149.gif Figure 37. LM2738X (1.6 MHz)
VBOOST Derived from Series Zener Diode (VIN)
15 V to 1.5 V / 1.5 A

8.2.4.1 Detailed Design Procedure

Table 5. Bill of Materials for Figure 37

PART ID PART VALUE PART NUMBER MANUFACTURER
U1 1.5-A Buck Regulator LM2738X Texas Instruments
C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK
C2, Output Cap 47 µF, 6.3 V, X5R C3216X5ROJ476M TDK
C3, Boost Cap 0.1 µF, 16 V, X7R C1005X7R1C104K TDK
D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba
D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc.
D3, Zener Diode 11-V 350-Mw SOT-23 BZX84C11T Diodes, Inc.
L1 3.3 µH, 3.5 A MSS7341-332NL Coilcraft
R1 8.87 kΩ, 1% CRCW06038871F Vishay
R2 10.2 kΩ, 1% CRCW06031022F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay

8.2.5 LM2738X Circuit Example 5

LM2738 30049150.gif Figure 38. LM2738X (1.6 MHz)
VBOOST Derived from Series Zener Diode (VOUT)
15 V to 9 V / 1.5 A

8.2.5.1 Detailed Design Procedure

Table 6. Bill of Materials for Figure 38

PART ID PART VALUE PART NUMBER MANUFACTURER
U1 1.5-A Buck Regulator LM2738X Texas Instruments
C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK
C2, Output Cap 22 µF, 16 V, X5R C3216X5R1C226M TDK
C3, Boost Cap 0.1 µF, 16 V, X7R C1005X7R1C104K TDK
D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba
D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc.
D3, Zener Diode 4.3-V 350-mw SOT-23 BZX84C4V3 Diodes, Inc.
L1 6.2 µH, 2.5 A MSS7341-622NL Coilcraft
R1 102 kΩ, 1% CRCW06031023F Vishay
R2 10.2 kΩ, 1% CRCW06031022F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay

8.2.6 LM2738Y Circuit Example 6

LM2738 30049142.gif Figure 39. LM2738Y (550 kHz)
VBOOST Derived from VIN
5 V to 1.5 V / 1.5 A

8.2.6.1 Detailed Design Procedure

Table 7. Bill of Materials for Figure 39

PART ID PART VALUE PART NUMBER MANUFACTURER
U1 1.5-A Buck Regulator LM2738Y Texas Instruments
C1, Input Cap 10 µF, 6.3 V, X5R C3216X5ROJ106M TDK
C2, Output Cap 47 µF, 6.3 V, X5R C3216X5ROJ476M TDK
C3, Boost Cap 0.1 µF, 16 V, X7R C1005X7R1C104K TDK
D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba
D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc.
L1 6.2 µH, 2.5 A, MSS7341-622NL Coilcraft
R1 8.87 kΩ, 1% CRCW06038871F Vishay
R2 10.2 kΩ, 1% CRCW06031022F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay

8.2.6.2 Application Curve

LM2738 30049131.png
VOUT = 1.5 V
Figure 40. Efficiency vs Load Current – Y Version

8.2.7 LM2738Y Circuit Example 7

LM2738 30049193.png Figure 41. LM2738Y (550 kHz)
VBOOST Derived from VOUT
12 V to 3.3 V / 1.5 A

8.2.7.1 Detailed Design Procedure

Table 8. Bill of Materials for Figure 41

PART ID PART VALUE PART NUMBER MANUFACTURER
U1 1.5-A Buck Regulator LM2738Y Texas Instruments
C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK
C2, Output Cap 47 µF, 6.3 V, X5R C3216X5ROJ476M TDK
C3, Boost Cap 0.1 µF, 16 V, X7R C1005X7R1C104K TDK
D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba
D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Vishay
L1 12 µH, 1.7 A, MSS7341-123NL Coilcraft
R1 31.6 kΩ, 1% CRCW06033162F Vishay
R2 10 kΩ, 1% CRCW06031002F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay

8.2.7.2 Application Curve

LM2738 30049152.png
VOUT = 3.3 V
Figure 42. Efficiency vs Load Current – Y Version

8.2.8 LM2738Y Circuit Example 8

LM2738 30049144.gif Figure 43. LM2738Y (550 kHz)
VBOOST Derived from VSHUNT
18 V to 1.5 V / 1.5 A

8.2.8.1 Detailed Design Procedure

Table 9. Bill of Materials for Figure 43

PART ID PART VALUE PART NUMBER MANUFACTURER
U1 1.5-A Buck Regulator LM2738Y Texas Instruments
C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK
C2, Output Cap (47 µF, 6.3 V, X5R) × 2 = 94 µF C3216X5ROJ476M TDK
C3, Boost Cap 0.1 µF, 16 V, X7R C1005X7R1C104K TDK
C4, Shunt Cap 0.1 µF, 6.3 V, X5R C1005X5R0J104K TDK
D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba
D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc.
D3, Zener Diode 5.1-V 250-Mw SOT-23 BZX84C5V1 Vishay
L1 8.7 µH, 2.2 A MSS7341-872NL Coilcraft
R1 8.87 kΩ, 1% CRCW06038871F Vishay
R2 10.2 kΩ, 1% CRCW06031022F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay
R4 4.12 kΩ, 1% CRCW06034121F Vishay

8.2.8.2 Application Curve

LM2738 30049131.png
VOUT = 1.5 V
Figure 44. Efficiency vs Load Current – Y Version

8.2.9 LM2738Y Circuit Example 9

LM2738 30049149.gif Figure 45. LM2738Y (550 kHz)
VBOOST Derived from Series Zener Diode (VIN)
15 V to 1.5 V / 1.5 A

8.2.9.1 Detailed Design Procedure

Table 10. Bill of Materials for Figure 45

PART ID PART VALUE PART NUMBER MANUFACTURER
U1 1.5-A Buck Regulator LM2738Y Texas Instruments
C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK
C2, Output Cap (47 µF, 6.3 V, X5R) × 2 = 94 µF C3216X5ROJ476M TDK
C3, Boost Cap 0.1 µF, 16 V, X7R C1005X7R1C104K TDK
D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba
D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc.
D3, Zener Diode 11-V 350-Mw SOT-23 BZX84C11T Diodes, Inc.
L1 8.7 µH, 2.2 A MSS7341-872NL Coilcraft
R1 8.87 kΩ, 1% CRCW06038871F Vishay
R2 10.2 kΩ, 1% CRCW06031022F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay

8.2.9.2 Application Curve

LM2738 30049131.png
VOUT = 1.5 V
Figure 46. Efficiency vs Load Current – Y Version

8.2.10 LM2738Y Circuit Example 10

LM2738 30049150.gif Figure 47. LM2738Y (550 kHz)
VBOOST Derived from Series Zener Diode (VOUT)
15 V to 9 V / 1.5 A

8.2.10.1 Detailed Design Procedure

Table 11. Bill of Materials for Figure 47

PART ID PART VALUE PART NUMBER MANUFACTURER
U1 1.5-A Buck Regulator LM2738Y Texas Instruments
C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK
C2, Output Cap 22 µF, 16 V, X5R C3216X5R1C226M TDK
C3, Boost Cap 0.1 µF, 16 V, X7R C1005X7R1C104K TDK
D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba
D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc.
D3, Zener Diode 4.3-V 350-mw SOT-23 BZX84C4V3 Diodes, Inc.
L1 15 µH, 2.1 A SLF7055T150M2R1-3PF TDK
R1 102 kΩ, 1% CRCW06031023F Vishay
R2 10.2 kΩ, 1% CRCW06031022F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay