UM10431 - NXP Semiconductors
Contents
1. es 019aaa740 w ee 019aaa739 Regulation mode Regulation mode a maximum gate voltage 9 7 V b gate voltage 6 1 V 1 Primary current 1 Primary current 2 Vcc 2 Vec 3 Ves 3 Vas 4 Vos 4 Vps Fig 14 Gate voltage UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 12 of 20 NXP Semiconductors U M1 0431 4 2 4 3 UM10431 GreenChip TEA1795T synchronous rectifier controller demo board lt i Maint iok gt gt gate discharged after aa blanking time J 019aaa741 Regulation mode Gate voltage rises very slowly in Regulation mode because the charge current is limited to 5 mA 1 Primary current 2 Vas 3 Vos Fig 15 Blanking time after MOSFET turned on If Vps rises above 25 mV the gate will be discharged until Vps is again equal to 25 mV and the IC remains in Regulation mode The gate is discharged through an internal MOSFET Rpson 24 Q A 5 mA current source provides the charge current ensuring the gate voltage rises see slowly rising edge in Figure 15 Regulation mode and turn off Regulation mode is provided in order to minimize turn off time In this mode the drain source voltage is stabilized independently of the value of the current at 25 mV see Figure 8 and Figure 14 If the current falls so low that2. 019aaa781 RX 3 9 KQ lioaqd 10 A 1 Transformer primary current 2 Vas 3 Vos Fig 10 DCM mode larger external filter A 1 pA max current flows through pins DSA and DSB Therefore in order to ensure the voltage drop across the resistors does not exceed 4 mV R1 R2 3 9 kQ All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 9 of 20 NXP Semiconductors UM10431 GreenChip TEA1795T synchronous rectifier controller demo board A schematic of the TEA1795T demo board v2 is shown in Figure 11 The differences between the two demo boards are summarized in Table 1 The component placement is shown in Figure 12 and Figure 13 MTHS heat sink T0220 Redpoint thermal pad Begquist T0220 HS2 Vout MTH1 MTH2 heat sink TO220 Redpoint thermal pad oo TO220 al c4 c5 c6 al c7 L1 L2 2200 uF 2200 uF 2200 uF 2200 uF Me 16V 16V 16V 16V MTH6 MTH3 MTH4 GND AH gt a1 J H R1 4 3 9 kQ D1 8 R3 7 vcc_ 4 GDA TEA1795_ GDB 102 6 D2 5 DSB it C8 C3 m C1 D3 l 150 pF BAUM T 220 nF i 220 nF T 150 pF WY BATI7 L3 3 L4 i 019aaa782 The schematic of the TEA1795T demo board v1 is identical but with component values changed as indicated in Table 1 Fig 11 Circuit diagram of the TEA1795T
3. 7 Legal information 00eeeeeenee 19 7 4 DetinitiONS 4 s246ce ee thera hes 19 7 2 Disclaimers 00000000 eee eee 19 7 3 TrademarkS 20000e eee eee 19 8 Contents oii sce centre ce eis dee a 20 Please be aware that important notices concerning this document and the product s described herein have been included in section Legal information NXP B V 2010 All rights reserved For more information please visit http Awww nxp com For sales office addresses please send an email to salesaddresses nxp com Date of release 26 October 2010 Document identifier UM10431
4. it s impossible to retain a drain source voltage of 25 mV the MOSFET will be turned off In Regulation mode the gate voltage is stabilized at just above the threshold voltage for turning off the MOSFET Therefore only a small fall in Vps is needed to turn off the MOSFET Compromise between turn on turn off and blanking times In Figure 16 a a small filter R1 3 9 kQ and C1 0 pF was added to reduce ringing As can be seen the turn on behavior is close to ideal However the premature turn off time is too long The gate pulse can be shifted to the right by increasing the value of Cx to 150 pF in this example see Figure 16 b and adding a clamping diode This improves the turn off behavior but results in a less ideal turn on time All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 13 of 20 NXP Semiconductors U M1 0431 GreenChip TEA1795T synchronous rectifier controller demo board Taira 10 019aaa786 019aaa787 a C1 O0pF b C1 150 pF clamping diode added 1 Transformer primary current 1 Vps 2 Vas 2 Ves 3 Vos Fig 16 Adjusting turn on turn off behavior The value of Cx should be selected such that the gate pulse is centered in relation to the MOSFET current An additional blanking time has been built in to prevent spurious switching after the MOSFET h
5. 2010 15 of 20 UM10431 GreenChip TEA1795T synchronous rectifier controller demo board NXP Semiconductors 5 PCB layout 5 1 Layout considerations To ensure optimal performance and to minimize impedance the following guidelines should be taken into account when designing the PCB layout e Dedicated tracks should be used to connect the sense pins on the IC to the MOSFET pins and the tracks should be as short as possible e The loop area between the drain sense track and the source sense track should be as small as possible dedicated tracks between sense pins and MOSFET t o6 GDS loop area as small as possible 019aaa908 1 DSA drain sense input MOSFET A 2 SSA source sense input MOSFET A 3 GDA gate driver output MOSFET A Fig 20 Layout recommendations UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved Rev 1 26 October 2010 16 of 20 User manual NXP Semiconductors U M1 0431 GreenChip TEA1795T synchronous rectifier controller demo board 5 2 Copper pattern SIGNOCREEN comp costge 5 12h 17622000 ORMAMED 1582 IGMAL LIZ dottemowide 422 P022 001711592 10 019aaa789 Fig 21 Layout of TEA1795T demo board v1 DPAK DEVELOPMENT TEAIT9S 7022 001 12751 SIGNACREEN romp cane siQAl 17022900 D212 12751 SIGNALSIZ Sotto aide i 42F22P022 001712781 019aaa790 Fig 22 Layout o
6. UM10431 GreenChip TEA1795T synchronous rectifier controller demo board Rev 1 26 October 2010 User manual Document information Info Content Keywords TEA1795T LLC converter resonant converter dual Synchronous Rectifier SR driver power supply demo board Abstract This user manual describes how the TEA1795T demo board can be used in a resonant converter In addition to the TEA1795T the demo board contains two power MOSFETs and output capacitors There are two versions of the demo board available 6 A 30 V and 20 A 12 V The demo board replaces the secondary part of the resonant converter excluding the feedback hardware NXP Semiconductors U M1 0431 GreenChip TEA1795T synchronous rectifier controller demo board Revision history Rev Date Description 1 0 20101026 First issue Contact information For more information please visit http www nxp com For sales office addresses please send an email to salesaddresses nxp com UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 2 of 20 NXP Semiconductors U M1 0431 GreenChip TEA1795T synchronous rectifier controller demo board 1 Introduction This document describes the TEA1795T demo board A functional description is provided supported by a set of measurements illustrating the performance of the TEA1795T The demo boa
7. ard It is possible to modify the TEA1795T demo board v2 to connect the heat sink to ground The demo boards were designed to be incorporated into an existing resonant power supply by replacing the secondary circuit The demo board is connected to the secondary side of the transformer Note that when replacing a diode in the high voltage line of the transformer with a MOSFET located in the ground path the center tap of the transformer must be disconnected from ground and connected to Vout see Figure 3 Note also that no provisions have been made to provide a feedback loop to control the output voltage of the demo board Therefore connections are needed between the two PCBs to close the loop see Figure 4 The points on the demo board where the secondary side of the transformer the feedback loop and the output wires should be connected are illustrated in Figure 5 UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 4 of 20 NXP Semiconductors UM10431 UM10431 GreenChip TEA1795T synchronous rectifier controller demo board replace diode with MOSFET dpi PI PEK gt e connect to GND instead of Vout i gt connect to Vo instead of GND connect to GND instead of Vout gt gt a replace diode with MOSFET Rei 019aaa775 Fig 3 Connecting
8. ary current 1 Transformer primary current 2 Ves 2 Ves 3 Vos 3 Vos Fig 8 DCM mode small internal filter When the filter design is determined primarily by the value of the parasitic inductance TO220 package the voltage on the capacitor is clamped by a MOSFET or by an RF diode with a low voltage drop to avoid a lengthy discharge time UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 8 of 20 NXP Semiconductors U M1 0431 UM10431 GreenChip TEA1795T synchronous rectifier controller demo board Adding an external filter reduces the premature turn off time but increases the turn on delay time Ideally the turn on delay and premature turn off times should be equal The increase in the turn on delay time can be limited by adding a clamping diode over Cx see Figure 9 gt lt turn on delay with diode gt lt turn on delay without diode lt i Maint ook gt gt premature turn off 019aaa737 Rx 3 9 KQ Cx 68 pF lioag 10 A 1 Transformer primary current 2 Ves 3 Vos Fig 9 DCM mode small external filter added Increasing the size of the capacitor will increase the turn on delay time and reduce the premature turn off time shifting the waveform to the right see Figure 10 T 1 Cx 136 pF Cx 68 pF
9. as been turned off see Figure 17 blanking time gt lt T ainra 33 gt ral i 1 Vas Half bridge point 3 Vos Fig 17 Blanking time after MOSFET turned off BR When the blanking time has expired it is possible to charge the gate and turn the MOSFET on again so multiple pulses are possible see Figure 18 UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 14 of 20 UM10431 GreenChip TEA1795T synchronous rectifier controller demo board NXP Semiconductors 019aaa785 1 Primary half bridge voltage De 2 Primary current 3 Vos 4 Vas Fig 18 Multiple turn on pulses 4 4 Parasitic turn on When Vps gt 12 mV an internal sink MOSFET is turned on However it might not start conducting immediately due to an internal delay in the IC reducing sinking capability During the rising edge on Ves the MOSFET will be turned on by the Miller capacitance of the MOSFET This is illustrated in Figure 19 67 0ns 174x 14 92537MHZ parasitic turn on 019aaa788 1 Primary current 2 Vas 3 Vos Fig 19 Parasitic turn on due to rising edge on Vps UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October
10. demo board v2 Table 1 Differences between demo boards Component TEA1795T demo board v1 C1 C2 C4 C5 C6 C7 D3 D4 HS1 HS2 Q1 Q2 not mounted not mounted 1000 uF 20 35 V Rubycon ZL 1000 uF 20 35 V Rubycon ZL 1000 uF 20 35 V Rubycon ZL 1000 uF 20 35 V Rubycon ZL not mounted not mounted heat sink FK 244 08 D PAK Fischer heat sink FK 244 08 D PAK Fischer PSMN025 100D NXP Semiconductors PSMN025 100D NXP Semiconductors TEA1795T demo board v2 150 pF 10 50 V NPO 150 pF 10 50 V NPO 2200 pF 20 16 V Rubycon ZL 2200 uF 20 16 V Rubycon ZL 2200 uF 20 16 V Rubycon ZL 2200 uF 20 16 V Rubycon ZL BAT17 BAT17 heat sink T0220 Redpoint heat sink TO220 Redpoint PSMN4R5 40PS NXP Semiconductors PSMN4R5 40PS NXP Semiconductors 1 C1 C2 D3 and D4 are included in the schematic diagram Figure 12 and PCB layout drawings Figure 21 and Figure 22 but are not mounted on the TEA1795T demo board v1 UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 10 of 20 NXP Semiconductors UM1 0431 GreenChip TEA1795T synchronous rectifier controller demo board jumper 10 Q HS1 PSMNO25 100D 5 _ V Br pss 100 V I Sour Robson 25 MQ ic Q2 C7 e eo TEA1795T N1 0 4 x 1000 uF 35 V Rub
11. eral damages the entire liability of NXP Semiconductors its affiliates and their suppliers and customer s exclusive remedy for all of the foregoing shall be limited to actual damages incurred by customer based on reasonable reliance up to the greater of the amount actually paid by customer for the product or five dollars US 5 00 The foregoing limitations exclusions and disclaimers shall apply to the maximum extent permitted by applicable law even if any remedy fails of its essential purpose 7 3 Trademarks Notice All referenced brands product names service names and trademarks are the property of their respective owners NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 19 of 20 NXP Semiconductors U M1 0431 GreenChip TEA1795T synchronous rectifier controller demo board 8 Contents 1 Introduction 2 00 c eee ee eee 3 2 The TEA1795 ssrseisronreicone reepa 3 3 Demo board setup ssssssusssrnnsnenne 4 4 Operati siss iiaia ee wie ee ee ee Aes 12 4 1 Turn on and blanking time 12 4 2 Regulation mode and turn off 13 4 3 Compromise between turn on turn off and blanking times 00 00 e eee eee 13 4 4 Parasitic turn on 1 2 0 0 ee eee ee eee 15 5 PCB layout ia eee eee ease eee teens 16 5 1 Layout considerations 16 5 2 Copper pattern 0 0 eee eee 17 6 Bill of materials 0 0 00 e eee eee 18
12. ergquist TO220 TEA1795T N1 micro shunt pitch 2 54 mm jumper or equivalent not mounted not mounted not mounted not mounted PSMN4R5 40PS NXP Semiconductors PSMN4R5 40PS NXP Semiconductors 3 9 kO 1 0 1 W 3 9 kO 1 0 1 W 10 O 1 0 1 W UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 18 of 20 NXP Semiconductors UM10431 GreenChip TEA1795T synchronous rectifier controller demo board 7 Legal information 7 1 Definitions Draft The document is a draft version only The content is still under internal review and subject to formal approval which may result in modifications or additions NXP Semiconductors does not give any representations or warranties as to the accuracy or completeness of information included herein and shall have no liability for the consequences of use of such information 7 2 Disclaimers Limited warranty and liability Information in this document is believed to be accurate and reliable However NXP Semiconductors does not give any representations or warranties expressed or implied as to the accuracy or completeness of such information and shall have no liability for the consequences of use of such information In no event shall NXP Semiconductors be liable for any indirect incidental punitive special or consequential damages including without l
13. f TEA1795T demo board v2 TO220 UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 17 of 20 NXP Semiconductors UM10431 6 Bill of materials GreenChip TEA1795T synchronous rectifier controller demo board Table 2 Bill of materials Component C1 C2 C3 C4 C5 C6 C7 C8 D1 D2 D3 D4 HS1 HS2 IC1 J1 L1 L2 L3 L4 Q1 Q2 R1 R2 R3 TEA1795T demo board v1 not mounted not mounted 220 nF 10 50 V DC 1000 uF 20 35 V Rubycon ZL 1000 uF 20 35 V Rubycon ZL 1000 uF 20 35 V Rubycon ZL 1000 uF 20 35 V Rubycon ZL 220 nF 10 50 V DC X7R not mounted not mounted not mounted not mounted heat sink FK 244 08 D PAK Fischer heat sink FK 244 08 D PAK Fischer TEA1795T N1 micro shunt pitch 2 54 mm jumper or equivalent not mounted not mounted not mounted not mounted PSMN025 100D NXP Semiconductors PSMN025 100D NXP Semiconductors 3 9 kO 1 0 1 W 3 9 kO 1 0 1 W 10 9 1 0 1 W TEA1795T demo board v2 150 pF 10 50 V NPO 150 pF 10 50 V NPO 220 nF 10 50 V DC 2200 uF 20 16 V Rubycon ZL 2200 uF 20 16 V Rubycon ZL 2200 uF 20 16 V Rubycon ZL 2200 uF 20 16 V Rubycon ZL 220 nF 10 50 V DC X7R not mounted not mounted BAT17 BAT17 heat sink T0220 Redpoint thermal pad Bergquist TO220 heat sink T0220 Redpoint thermal pad B
14. hird party customer s NXP does not accept any liability in this respect Export control This document as well as the item s described herein may be subject to export control regulations Export might require a prior authorization from national authorities Evaluation products This product is provided on an as is and with all faults basis for evaluation purposes only NXP Semiconductors its affiliates and their suppliers expressly disclaim all warranties whether express implied or statutory including but not limited to the implied warranties of non infringement merchantability and fitness for a particular purpose The entire risk as to the quality or arising out of the use or performance of this product remains with customer In no event shall NXP Semiconductors its affiliates or their suppliers be liable to customer for any special indirect consequential punitive or incidental damages including without limitation damages for loss of business business interruption loss of use loss of data or information and the like arising out the use of or inability to use the product whether or not based on tort including negligence strict liability breach of contract breach of warranty or any other theory even if advised of the possibility of such damages Notwithstanding any damages that customer might incur for any reason whatsoever including without limitation all damages referenced above and all direct or gen
15. imitation lost profits lost savings business interruption costs related to the removal or replacement of any products or rework charges whether or not such damages are based on tort including negligence warranty breach of contract or any other legal theory Notwithstanding any damages that customer might incur for any reason whatsoever NXP Semiconductors aggregate and cumulative liability towards customer for the products described herein shall be limited in accordance with the Terms and conditions of commercial sale of NXP Semiconductors Right to make changes NXP Semiconductors reserves the right to make changes to information published in this document including without limitation specifications and product descriptions at any time and without notice This document supersedes and replaces all information supplied prior to the publication hereof Suitability for use NXP Semiconductors products are not designed authorized or warranted to be suitable for use in life support life critical or safety critical systems or equipment nor in applications where failure or malfunction of an NXP Semiconductors product can reasonably be expected to result in personal injury death or severe property or environmental damage NXP Semiconductors accepts no liability for inclusion and or use of NXP Semiconductors products in such equipment or applications and therefore such inclusion and or use is at the customer s own risk Applicat
16. ions Applications that are described herein for any of these products are for illustrative purposes only NXP Semiconductors makes no representation or warranty that such applications will be suitable for the specified use without further testing or modification Customers are responsible for the design and operation of their applications and products using NXP Semiconductors products and NXP Semiconductors accepts no liability for any assistance with applications or customer product UM10431 All information provided in this document is subject to legal disclaimers design It is customer s sole responsibility to determine whether the NXP Semiconductors product is suitable and fit for the customer s applications and products planned as well as for the planned application and use of customer s third party customer s Customers should provide appropriate design and operating safeguards to minimize the risks associated with their applications and products NXP Semiconductors does not accept any liability related to any default damage costs or problem which is based on any weakness or default in the customer s applications or products or the application or use by customer s third party customer s Customer is responsible for doing all necessary testing for the customer s applications and products using NXP Semiconductors products in order to avoid a default of the applications and the products or of the application or use by customer s t
17. ource voltage of the MOSFETs sense pins DSA and SSA are connected respectively to the drain and source of MOSFET A Sense pins DSB and SSB are connected to MOSFET B In addition to the voltage drop due to Rpgon of the All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 3 of 20 NXP Semiconductors U M1 0431 GreenChip TEA1795T synchronous rectifier controller demo board MOSFETs voltage drops are present across the tracks and the package Incorporating two separate sense pins SSA and SSB helps to minimize the influence of these voltage drops SSB Vcc TEA1795T GDB DSB 014aaa976 Fig 2 Pin configuration 3 Demo board setup To ensure the demo board can be used in a variety of applications two versions are available TEA1795T demo board v1 contains two NXP Semiconductors PSMN025 100D 100 V 25 mQ DPAK power MOSFETS and is intended for high voltage low current applications e g as a notebook adaptor TEA1795T demo board v2 contains two NXP Semiconductors PSMN4R5 40PS 40 V 4 5 mQ TO220 power MOSFETS and was designed for low voltage high current applications e g in a desktop PC power supply Because of the small heat sink included in the TEA1795T demo board v2 a fan should be used for forced cooling Remark The heat sinks are connected to the MOSFET drains in both versions of the demo bo
18. rd contains the secondary part of a single output LLC converter excluding the control hardware To use the demo board correctly an LLC converter board in which the secondary part can be replaced by the demo board is required Furthermore two sense wires need to be connected to the control hardware to provide the feedback loop for controlling the output voltage 2 The TEA1795T The TEA1795T is a dual Synchronous Rectifier SR driver IC or SR driver for resonant converters It can easily drive MOSFETs used to replace the rectifier diodes on the secondary side A simple control algorithm built into the IC determines when a MOSFET needs to be turned on or off at Vps 220 mV the MOSFET is turned on between 25 mV and 12 mV the IC will be in Regulation mode above 12 mV the MOSFET will be turned off In Regulation mode the drain source voltage is held constant at 25 mV to minimize turn off time A simplified state diagram of the TEA1795T is shown in Figure 1 The 25 mV level was built in to minimize the turn off delay time at the expense of additional dissipation In addition two blanking time periods were added to prevent spurious switching after a MOSFET is turned on or off Fig 1 Simplified state diagram of the TEA1795T Vps gt 220 mV Vps lt 25 mV Vps lt 220 mV Vps lt 25 mV Vps gt 25 mV Vps gt 12 mV 25 mV lt Vps lt 12 mV A 019aaa873 UM10431 To measure the drain s
19. s reserved User manual Rev 1 26 October 2010 6 of 20 NXP Semiconductors U M1 0431 GreenChip TEA1795T synchronous rectifier controller demo board N ringing 019aaa778 1 Transformer primary current 2 Vos Fig 6 Drain source ringing caused by MOSFET switching without filtering As discussed in application note AN10954 measurement of the drain source voltage includes voltage drops across the tracks bonding wires and the pins of the package These voltages drops are due in part to parasitic inductance which can lead to serious measurement errors The RC filters provided on the demo boards to filter out drain source ringing can also be used to compensate for parasitic inductance The influence of the parasitic inductance can be minimized by satisfying the following equation L 4 RxxCx x lor2 1 Rpson The magnitude of the parasitic inductance depends on the package used and is much higher in a T0220 package than in a DPAK package Drain source ringing is more of an issue with a DPAK package The dimensioning of the filters in the demo boards takes account of this RC filter tuning on the TEA1795T demo board v1 is biased towards filtering drain source ringing whereas the filters on the TEA1795T demo board v2 are optimized to reduce parasitic inductance With the TEA1795T demo board v2 the mode of operation of the converter needs to be taken into account The dimensions of
20. the compensation filter were calculated for Discontinuous Current Mode DCM The filter has not been optimized for Continuous Current Mode CCM and will need to be adjusted since parasitic inductance has less influence at the instant the MOSFET is turned off The plot in Figure 7 was measured with the converter in CCM mode C1 0 pF and ligag 10 A Parasitic inductance causes the MOSFETs to turn off too early premature turn off It is clear from Figure 7 and Figure 8 that the influence of parasitic inductance is much greater in DCM mode 1 2 us than in CCM mode 200 ns UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 7 of 20 NXP Semiconductors U M1 0431 GreenChip TEA1795T synchronous rectifier controller demo board premature turn off 019aaa738 Rx 3 9 KQ Cx 0 pF lioaa 10 A 1 Transformer primary current 2 Ves 3 Vos Fig 7 CCM mode small internal filter Regulation mode a 1 2 us gt e Bains 1Dk gt gt premature turn off 019aaa779 019aaa736 a Parasitic inductance causes the IC to switch to b 120 ns turn on delay time without external filter Regulation mode 1 2 us before the secondary current reaches 0 V Rx 3 9 kQ Cx 0 pF lioaa 10 A Rx 3 9 kQ Cx 0 pF lioaa 10 A 1 Transformer prim
21. the transformer to the demo board power supply 019aaa776 Fig 4 Connecting the control loop to the demo board All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 5 of 20 NXP Semiconductors UM10431 UM10431 GreenChip TEA1795T synchronous rectifier controller demo board Fig 5 OG ANZ Placement of demo board in existing resonant converter input capacitor Vi I IF ae a3 I TST TFT H resonant capacitor primary winding LNY YNV secondary winding to feedback n SR MOSFETs C6 TEA1795T N1 electrolytic capacitors 019aaa777 Low pass filters R1 amp C1 and R2 amp C2 are used to filter out ringing in the drain source voltage caused by the part of the secondary winding that is not coupled to the main secondary winding and the drain source capacitance This filtering is needed to prevent the MOSFETs being turned on by mistake A plot of the ringing in the drain source voltage is shown in Figure 6 Ringing occurs when one of the MOSFETs stops conducting current or when the half bridge voltage is changing rising falling All information provided in this document is subject to legal disclaimers NXP B V 2010 All right
22. ycon ZL 019aaa783 Fig 12 Component placement TEA1795T demo board v1 DPAK jumper 10 Q 220 nF Nf aiics PSMN4R5 40PS 50 V X7R s no cam C8 ia V BR DSS 40V Q eres J SE let mao o2 Rpgon 4 5 mQ oO e eee z eee PA ee Se Y e e TEA1795T N1 va 4 x 2200 uF 16 V Rubycon ZL 019aaa784 Fig 13 Component placement TEA1795T demo board v2 TO220 UM10431 All information provided in this document is subject to legal disclaimers NXP B V 2010 All rights reserved User manual Rev 1 26 October 2010 11 of 20 NXP Semiconductors UM1 0431 GreenChip TEA1795T synchronous rectifier controller demo board 4 Operation 4 1 Turn on and blanking time The MOSFETs are turned on when the drain source voltage falls below the turn on threshold 220 mV and the gate is charged An internal clamping circuit limits the maximum gate voltage to approximately 10 V see Figure 14 a The minimum gate voltage Ves will be 6 V when Vcc is at a minimum x8 V A blanking time of 520 ns is built in to prevent the MOSFET turning off again immediately after turning on After the blanking time the gate voltage remains at the same level or is partly or totally discharged In the plots in Figure 14 the gate remains charged In the plot in Figure 15 the gate is discharged after the blanking time Te Moins zik 57 7 3 lt lt Paini 20k 53
Download Pdf Manuals
Related Search