Energy Saving Products
101 N.Sepulveda Blvd, EL Segundo 90245 California, USA
IRAC27951SR
IRS27951 Evaluation Board
User Guide
Rev. 4.1
6/1/2011
International Rectifier
Page 1 of 23
PROPRIETARY INFORMATION
- This document and the information contained therein are proprietary and are not to be reproduced, used or disclosed
to others for manufacture or any other purpose except as specifically authorized in writing by
INTERNATIONAL RECTIFIER.
Table of Contents
1
2
3
4
4.1
4.2
4.3
4.4
4.5
4.6
5
5.1
5.2
5.3
5.4
6
6.1
6.2
6.3
6.4
6.5
6.6
6.7
7
7.1
7.2
7.3
INTRODUCTION ........................................................................................................................ 3
IRS27951/2 DESCRIPTION ....................................................................................................... 3
IR11682 DESCRIPTION ............................................................................................................ 4
EVALUATION BOARD SPECIFICATIONS ................................................................................ 5
Board Description ................................................................................................................... 5
Schematic ............................................................................................................................... 6
Evaluation Board Picture ........................................................................................................ 7
Board Component Placement ................................................................................................. 7
Board PCB Layout .................................................................................................................. 8
Bill of Materials ....................................................................................................................... 9
EVALUATION BOARD OPERATING PROCEDURE ............................................................... 10
Load Connection................................................................................................................... 10
AC/DC Input ......................................................................................................................... 10
IRS27951 DC Supply Voltage .............................................................................................. 11
Disconnect the Board ........................................................................................................... 11
SYSTEM PERFORMANCE CHARACTERIZATION ................................................................ 12
Steady-State and Start-up Waveforms ................................................................................. 12
Synchronous Rectifier Waveform ......................................................................................... 15
Dynamic Load Response & Output Voltage Regulation ....................................................... 16
Output Ripple ........................................................................................................................ 19
User Initiated SLEEP Mode .................................................................................................. 20
Efficiency Chart..................................................................................................................... 21
Thermal Data ........................................................................................................................ 22
Transformer Spec..................................................................................................................... 22
Electrical Diagram................................................................................................................. 22
Resonant Transformer Winding Position on Coil former ....................................................... 23
Resonant Transformer Winding Characteristics ................................................................... 23
Rev. 4.1
6/1/2011
International Rectifier
Page 2 of 23
PROPRIETARY INFORMATION
- This document and the information contained therein are proprietary and are not to be reproduced, used or disclosed
to others for manufacture or any other purpose except as specifically authorized in writing by
INTERNATIONAL RECTIFIER.
1 INTRODUCTION
This document details the test procedure for validation of IRAC27951SR-240W Evaluation Board,
featuring the IRS27951 Resonant Half Bridge controller and the IR11682 dual-channel synchronous
rectification controller. The document includes schematic diagram, test setup, test procedure, and test
results.
2 IRS27951/2 DESCRIPTION
The IRS2795(1,2) is an 8 pin, high-voltage, double-ended controller specific for the resonant half-bridge
topology. It provides 50% complementary duty cycle; the high-side and the low-side devices are driven 180°
out-of-phase for exactly the same time. The IC incorporates additional protection features for robust operation
and provides a high performance solution while minimizing external components and printed circuit board area.
The IC enables the designer to externally program all the following features using a 2 pin oscillator - operating
frequency range (minimum and maximum frequency), startup frequency, dead time, soft-start time and sleep
mode. Each of these functions are programmed as follows –
The minimum frequency is programmed using RT and CT.
The dead time is programmed using CT.
RSS and CSS program the converter soft-start time.
RSS//RT and CT program the converter start-up frequency.
The converter maximum frequency is set by (Rmax//RT) and CT.
Sleep mode is initiated by pulling the CT/SD to COM.
At start-up, to prevent uncontrolled inrush current, the switching frequency starts from a programmable
maximum value and progressively decays until it reaches the steady-state value determined by the control
loop. This frequency shift is non linear to minimize output voltage overshoot and its duration is programmable
as well. Output voltage regulation is obtained by modulating the operating frequency. An externally
programmable dead time is inserted between the turn-OFF of one switch and the turn-ON of the other one
allows device zero-voltage turn-on transitions.
IRS2795 uses IR’s proprietary high-voltage technology to implement a VS sensing circuitry that monitors the
current through the low-side half bridge MOSFET for short circuit faults. By using the R
DSON
of the low-side
MOSFET, the IRS2795 eliminates the need for an additional current sensing resistor, filter and current-sensing
pin. This protection feature is latched and the thresholds are fixed at
2V for IRS27951
and
3V for IRS27952.
Finally, the controller IC also features a micro power startup current (I
CC
<100µA) and a user initiated sleep
mode during which the IC power consumption is less than 200µA (@ Vcc=15V). The sleep mode function
allows system designs with reduced standby power consumption and can be used to meet stringent energy
standards from Blue Angel, Energy Star etc.
Rev. 4.1
6/1/2011
International Rectifier
Page 3 of 23
PROPRIETARY INFORMATION
- This document and the information contained therein are proprietary and are not to be reproduced, used or disclosed
to others for manufacture or any other purpose except as specifically authorized in writing by
INTERNATIONAL RECTIFIER.
3 IR11682 DESCRIPTION
IR11682 is a secondary-side SmartRectifier
TM
driver IC designed to drive two N-Channel power MOSFETs
used as synchronous rectifiers in resonant converter applications. The IC can control one or more paralleled N
MOSFETs to emulate the behavior of Schottky diode rectifiers. The drain to source for each rectifier MOSFET
voltage is sensed differentially to determine the level of the current and the power switch is turned ON and
OFF in close proximity of the zero current transition.
When the conduction phase of the SR FET is initiated, current will start flowing through its body diode,
generating a negative VDS voltage across it. The body diode has generally a much higher voltage drop than
the one caused by the MOSFET on resistance and therefore will trigger the turn-on threshold V
TH2
. When V
TH2
is triggered, IR11682 will drive the gate of MOSFET on which will in turn cause the conduction voltage VDS to
drop down to ID*RDSON. This drop is usually accompanied by some amount of ringing, that could trigger the
input comparator to turn off; hence, a fixed Minimum On Time (MOT) blanking period is used that will maintain
the power MOSFET on for a minimum amount of time.
Once the SR MOSFET has been turned on, it will remain on until the rectified current will decay to the level
where VDS will cross the turn-off threshold V
TH1
. Once the threshold is crossed, the current will start flowing
again through the body diode, causing the VDS voltage to jump negative. Hence, V
TH2
is blanked for a time
duration t
BLANK
after V
TH1
is triggered. When the device VDS crosses the positive reset threshold V
TH3
, t
BLANK
is
terminated and the IC is ready for next conduction cycle as shown below.
V
TH3
I
DS
V
DS
T1
V
TH1
T2
V
TH2
Gate Drive
Blanking
MOT
t
BLANK
time
IR11682 further simplifies synchronous rectifier control by offering the following power management features:
- Wide VCC operating range allows the IC to be directly powered from the converter output
- Shoot through protection logic that prevents both the GATE outputs from the IC to be high at the same time
- Device turn ON and OFF in close proximity of the zero current transition with low turn-on and turn-off
propagation delays; eliminates reactive power flow between the output capacitors and power transformer
- Cycle-by-cycle MOT protection circuit can automatically detect no load condition and turn off gate driver
output to avoid negative current flowing through the MOSFETs
- Internally clamped gate driver outputs that significantly reduce gate losses
Rev. 4.1
6/1/2011
International Rectifier
Page 4 of 23
PROPRIETARY INFORMATION
- This document and the information contained therein are proprietary and are not to be reproduced, used or disclosed
to others for manufacture or any other purpose except as specifically authorized in writing by
INTERNATIONAL RECTIFIER.
4 EVALUATION BOARD
1
SPECIFICATIONS
Input Voltage...……….……………………………………………………………….280VAC or 400VDC
AC Line Frequency Range…………………………………………………………..47 – 63Hz
Converter Switching Frequency Range…………………………………………….70-150 kHz
Converter Output....…………………………………………………………………..24V/10A
Maximum Output Power…………………………………………………………......240W
Minimum Load Requirement…………………………………………………………None
Maximum Ambient Operating Temperature………………………………………..40°C
2
Efficiency (@ 240W)……...…………………………………………….……….……. 95%
Short Circuit Protection………………………....……………………………………. Yes
Double Layer PCB with 2oz Copper
There are high voltages present whenever the board is energized and proper precautions should be
taken to avoid potential shock and personal injury.
4.1 Board Description
The evaluation board consists of a front-end AC-DC rectifier stage cascaded with a half-bridge resonant DC-
DC converter with 24V output voltage rail.
The front end is a conventional rectifier stage with a rectifier bridge and an EMI filter.
The downstream converter is a multi-resonant half bridge LLC converter whose control is implemented with the
IRS27951 (U1) controller HVIC. The controller drives the two half-bridge MOSFETs with a 50 percent fixed
duty cycle with dead-time, changing the frequency according to the feedback signal in order to regulate the
output voltage against load and input voltage variations. As described earlier, in addition to current protection,
all the critical functions needed to control resonant converter designs can be externally programmed using this
8 pin controller IC.
IRS27951 is self-supplied in this reference design. The startup resistors Rstart1~Rstart3 provide startup
current to IRS27951 during power up and charge the Vcc capacitors (CDC2 and CVcc1). Once Vcc voltage
exceeds Vccuv+ threshold, IRS27951 starts operation and the auxiliary winding of power transformer can
1
Please note that EMI measurements have not been performed on this evaluation board. The primary goal of this board is to verify the functionality of
the IRS27951 controller IC.
A fan is recommended whenever operating at the maximum load for a prolonged period of time.
2
Rev. 4.1
6/1/2011
International Rectifier
Page 5 of 23
PROPRIETARY INFORMATION
- This document and the information contained therein are proprietary and are not to be reproduced, used or disclosed
to others for manufacture or any other purpose except as specifically authorized in writing by
INTERNATIONAL RECTIFIER.
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