User's Guide
SNVA633A – March 2012 – Revised April 2013
AN-2202 LM34927 Integrated Secondary Side Bias
Regulator for Isolated DC-DC Converters
1
Introduction
An isolated bias supply is implemented in this evaluation board with LM34927 Constant-On-Time
regulator. The LM34927 regulator integrates both the high and low side power switches essential for
creating isolated buck converter.
The board specifications are as follows:
• Input Range: 20 V to 100 V
• Primary Output Voltage: 10 V
• Secondary (Isolated) Output Voltage: 9.5 V
• Maximum Load Current (Primary + Secondary): 300 mA
• Maximum Power Output: 3 W
• Nominal Switching Frequency: 750 kHz
• Efficiency (FIN = 48 V, IOUT2 = 300 mA): 76 percent
• Board size: 2 inch x 2 inch
All trademarks are the property of their respective owners.
SNVA633A – March 2012 – Revised April 2013
Submit Documentation Feedback
AN-2202 LM34927 Integrated Secondary Side Bias Regulator for Isolated
DC-DC Converters
Copyright © 2012–2013, Texas Instruments Incorporated
1
UVLO Threshold and Hysteresis
www.ti.com
Figure 1. LM34927 Evaluation Board (Top View)
2
UVLO Threshold and Hysteresis
The UVLO resistors are selected using the following two equations:
VIN(HYS) = IHYSR1
(1)
and
VIN
(UVLO,rising)
= 1.225V x §
R1
© R2
+1·
¹
(2)
On this evaluation board R1 = 127 kΩ and R2 = 8.25 kΩ, resulting in UVLO rising threshold at VIN = 20.5
V and a hysteresis of 2.54 V.
3
Board Connection And Start-Up
The input connections are made using TP1 (VIN) and TP2 (GND) terminals. The primary output appears
at TP3 (VOUT1) and TP4 (GND). The secondary (isolated) output is available across TP5 (VOUT2) and
TP6 (IGND). The input voltage should be gradually increased above UVLO set point of 20.5 V. Both the
outputs (VOUT1 and VOUT2) should be close to 10 V at this point. This board is designed to function with
input voltage range of 20 V to 100 V. The minimum VIN threshold can be changed by changing the UVLO
resistors R1, R2. VIN should not exceed 100 V.
2
AN-2202 LM34927 Integrated Secondary Side Bias Regulator for Isolated
DC-DC Converters
Copyright © 2012–2013, Texas Instruments Incorporated
SNVA633A – March 2012 – Revised April 2013
Submit Documentation Feedback
Board Connection And Start-Up
www.ti.com
The magnetics in this design is optimized for solution size, and therefore limits the output power. The total
load at the output should not exceed 300 mA otherwise the coupled inductor will saturate/overheat
which can destroy both the coupled inductor and the regulator IC U1. If a sustained over-current
situation is to be tolerated, a coupled inductor with higher saturation and rms ratings should be used. The
board schematic is shown in Figure 2.
D1
VOUT2
9.5V
R7
0Ÿ
SW
(TP11)
T1
20V-100V
VIN
(TP1)
BST
2
4
C1 +
2.2 F
GND
(TP2)
+
C5
0.47 F
R3
130 NŸ
SW
VIN
7
8
+ 0.01 F
C2
R8
RON
LM34927
46.4 NŸ
33 H
(1:1)
VCC
UVLO
FB
(TP7)
R2
UVLO 8.25 NŸ
EXP
TP8
TP10
RTN
1
6
C9
2200 pF
2000V
R9
0Ÿ
(TP5)
VOUT1
10V
(TP3)
0Ÿ
R6
C7
C8
0.1 F
D2
R4
7.32 NŸ
+ C3
1 F
GND
(TP4)
5
+
U1
IGND
3300 pF
R1
127 NŸ
3
(TP6)
+ C4 2 NŸ
1 F
C6
1 F
R5
1 NŸ
Figure 2. Complete Evaluation Board Schematic
SNVA633A – March 2012 – Revised April 2013
Submit Documentation Feedback
AN-2202 LM34927 Integrated Secondary Side Bias Regulator for Isolated
DC-DC Converters
Copyright © 2012–2013, Texas Instruments Incorporated
3
Bill of Materials
4
www.ti.com
Bill of Materials
Table 1. Bill of Materials
Item
Description
Mfg., Part Number
Package
Value
U1
Sync Switching
Regulator
Texas Instruments, LM34927
LLP-8
100V, 0.6A
T1
Coupled Inductor,
1500 VDC
Coilcraft, LPD5030V-333ME
5mm x 5mm
33uH, 0.47A
Alternate Part
Wurth, 750312750
8.26mm x
6.60mm
22uH, 0.76A
Schottky Diode
Diodes Inc., DFLS1100-7
Pwr–DI123
100V, 1A
D2
Schottky Diode
Diodes Inc., SDM10U45-7
SOD–523
40V, 100mA
C1
Ceramic Capacitor
TDK, C3225X7R2A225K
1210
2.2uF, 100V, X7R
D1
4
C2
Ceramic Capacitor
TDK, C1608X7R1C103K
0603
0.01uF, 16V, X7R
C3, C4
Ceramic Capacitor
TDK, C2012X7R1E105K
0805
1uF, 25V, X7R
C5
Ceramic Capacitor
Murata, GRM21BR72A474KA73L
0805
0.47uF, 100V,
X7R
C6
Ceramic Capacitor
TDK, C1608X7R1C105K
0603
1uF, 16V, X7R
C7
Ceramic Capacitor
Murata, GRM188R72A332KA01D
0603
3300pF, 100V, +/5%
C8
Ceramic Capacitor
AVX, 0603YC104KAT2A
0603
0.1uF, 16V, X7R
C9
Ceramic Capacitor
Johanson, 202R29W222KV4E
1808
2200pF, 2000V,
X7R
R1
Resistor
Vishay/Dale, CRCW0805127KFKEA
0805
127k ohm, 1%
R2
Resistor
Vishay/Dale, CRCW08058K25FKEA
0805
8.25k ohm, 1%
R3
Resistor
Vishay/Dale, CRCW0805130KFKEA
0805
130k ohm, 1%
R4
Resistor
Panasonic, ERJ-3EKF7321V
0603
7.32k ohm, 1%
R5
Resistor
Panasonic, ERJ-3EKF1001V
0603
1.0k ohm, 1%
R6
Resistor
Yageo, RC0603JR-070RL
0603
0 ohm
R7, R9
Resistor
Yageo, RC0603JR-070RL
0603
0 ohm
R8
Resistor
Panasonic, ERJ-3EKF4642V
0603
46.4k ohm, 1%
R10
Resistor
Panasonic, ERJ-6GEYJ202V
0805
2k ohm, 5%
AN-2202 LM34927 Integrated Secondary Side Bias Regulator for Isolated
DC-DC Converters
Copyright © 2012–2013, Texas Instruments Incorporated
SNVA633A – March 2012 – Revised April 2013
Submit Documentation Feedback
Performance Curves
www.ti.com
5
Performance Curves
Figure 3. Efficiency at 750 kHz, VOUT1=10V
Figure 4. Steady State Waveform (VIN=48V, IOUT1= 100mA, IOUT2= 200mA)
Figure 5. Step Load Response (VIN=48V, IOUT1=0, Step Load on IOUT2=100mA to 200mA)
SNVA633A – March 2012 – Revised April 2013
Submit Documentation Feedback
AN-2202 LM34927 Integrated Secondary Side Bias Regulator for Isolated
DC-DC Converters
Copyright © 2012–2013, Texas Instruments Incorporated
5
PC Board Layout
6
www.ti.com
PC Board Layout
Figure 6. Board Silkscreen
6
AN-2202 LM34927 Integrated Secondary Side Bias Regulator for Isolated
DC-DC Converters
Copyright © 2012–2013, Texas Instruments Incorporated
SNVA633A – March 2012 – Revised April 2013
Submit Documentation Feedback
PC Board Layout
www.ti.com
Figure 7. Board Top Layer
SNVA633A – March 2012 – Revised April 2013
Submit Documentation Feedback
AN-2202 LM34927 Integrated Secondary Side Bias Regulator for Isolated
DC-DC Converters
Copyright © 2012–2013, Texas Instruments Incorporated
7
PC Board Layout
www.ti.com
Figure 8. Board Bottom Layer
8
AN-2202 LM34927 Integrated Secondary Side Bias Regulator for Isolated
DC-DC Converters
Copyright © 2012–2013, Texas Instruments Incorporated
SNVA633A – March 2012 – Revised April 2013
Submit Documentation Feedback
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other
changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest
issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and
complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale
supplied at the time of order acknowledgment.
TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms
and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary
to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily
performed.
TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and
applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information
published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or
endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration
and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered
documentation. Information of third parties may be subject to additional restrictions.
Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service
voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.
TI is not responsible or liable for any such statements.
Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements
concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support
that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which
anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause
harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use
of any TI components in safety-critical applications.
In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to
help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and
requirements. Nonetheless, such components are subject to these terms.
No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties
have executed a special agreement specifically governing such use.
Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in
military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components
which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and
regulatory requirements in connection with such use.
TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of
non-designated products, TI will not be responsible for any failure to meet ISO/TS16949.
Products
Applications
Audio
www.ti.com/audio
Automotive and Transportation
www.ti.com/automotive
Amplifiers
amplifier.ti.com
Communications and Telecom
www.ti.com/communications
Data Converters
dataconverter.ti.com
Computers and Peripherals
www.ti.com/computers
DLP® Products
www.dlp.com
Consumer Electronics
www.ti.com/consumer-apps
DSP
dsp.ti.com
Energy and Lighting
www.ti.com/energy
Clocks and Timers
www.ti.com/clocks
Industrial
www.ti.com/industrial
Interface
interface.ti.com
Medical
www.ti.com/medical
Logic
logic.ti.com
Security
www.ti.com/security
Power Mgmt
power.ti.com
Space, Avionics and Defense
www.ti.com/space-avionics-defense
Microcontrollers
microcontroller.ti.com
Video and Imaging
www.ti.com/video
RFID
www.ti-rfid.com
OMAP Applications Processors
www.ti.com/omap
TI E2E Community
e2e.ti.com
Wireless Connectivity
www.ti.com/wirelessconnectivity
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2013, Texas Instruments Incorporated