MP6908A
Fast Turn-Off Intelligent Rectifier
with No Need for Auxiliary Winding
DESCRIPTION
FEATURES
The MP6908A is a low-drop diode emulator IC
that, when combined with an external switch,
replaces Schottky diodes in high-efficiency
flyback converters. The MP6908A regulates the
forward drop of an external synchronous
rectifier (SR) MOSFET to about 40mV, which
switches off once the voltage becomes negative.
The MP6908A can generate its own supply
voltage for battery charging applications with a
potential low output voltage. The MP6908A can
also generate this voltage at short-circuit output
conditions or high-side SR configurations.
Programmable ringing detection circuitry
prevents the MP6908A from turning on falsely
at VDS oscillations during discontinuous
conduction mode (DCM) and quasi-resonant
operation.
The MP6908A is available in a space-saving
TSOT23-6 package.
Supports DCM, CCM, Quasi-Resonant
Operations and Active Clamp Flyback
Supports
up
to
600kHz
Switching
Frequency
Wide Output Range down to 0V, No Short
Circuit Current Flows through Body Diode
No Need for Auxiliary Winding for High-Side
or Low-Side Rectification
Ringing Detection Prevents False Turn-On
during
DCM
and
Quasi-Resonant
Operations
Works with Standard and Logic Level SR
MOSFETs
Compatible with Energy Star Standards
~30ns Fast Turn-Off and Turn-On Delay
~100µA Quiescent Current
Supports both High-Side and Low-Side
Rectification
Available in a TSOT23-6 Package
APPLICATIONS
USB PD Quick Chargers
Adaptors
Flyback Power Supplies with Very Low
and/or Variable Output Voltage
All MPS parts are lead-free, halogen-free, and adhere to the RoHS directive. For
MPS green status, please visit the MPS website under Quality Assurance.
“MPS”, the MPS logo, and “Simple, Easy Solutions” are trademarks of
Monolithic Power Systems, Inc. or its subsidiaries.
TYPICAL APPLICATION
MP6908A Rev. 1.1
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5/27/2020
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1
MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
ORDERING INFORMATION
Part Number*
MP6908AGJ
Package
TSOT23-6
Top Marking
See Below
* For Tape & Reel, add suffix –Z (e.g.: MP6908AGJ–Z).
TOP MARKING
BHJ: Product code of MP6908AGJ
Y: Year code
PACKAGE REFERENCE
TOP VIEW
TSOT23-6
MP6908A Rev. 1.1
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MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
PIN FUNCTIONS
Pin #
1
2
Name
HVC
VSS
3
SLEW
4
VDD
VG
VD
5
6
Description
HV linear regulator input.
Ground. VSS is used as a MOSFET source sense reference for VD.
Programming to turn on the signal slew rate detection. SLEW prevents the SR
controller from turning on falsely by ringing below the turn-on threshold at VD in
discontinuous conduction mode (DCM) and quasi-resonant mode. Any signal slower than
the pre-set slew rate cannot turn on VG.
Linear regulator output. VDD is the supply of the MP6908A.
Gate drive output.
MOSFET drain voltage sense.
ABSOLUTE MAXIMUM RATINGS (1)
Thermal Resistance (4)
VDD, VG to VSS ........................... -0.3V to +14V
VD, HVC to VSS ............................ -1V to +180V
SLEW to VSS ............................... -0.3V to +6.5V
Continuous power dissipation (TA = +25°C)(2)
................................................................... 0.56W
Junction temperature ................................ 150°C
Lead temperature (solder) ........................ 260°C
Storage temperature .................-55°C to +150°C
TSOT23-6 ............................ 220 ..... 110 .... °C/W
Recommended Operation Conditions (3)
VDD to VSS ........................................ 4V to 13V
VD, HVC to VSS ............................ -1V to +150V
Maximum junction temperature (TJ) ......... 125°C
θJA
θJC
NOTES:
1) Exceeding these ratings may damage the device.
2) The maximum allowable power dissipation is a function of the
maximum junction temperature TJ(MAX), the junction-toambient thermal resistance θJA, and the ambient temperature
TA. The maximum allowable continuous power dissipation at
any ambient temperature is calculated by PD(MAX)=(TJ(MAX)TA)/θJA. Exceeding the maximum allowable power dissipation
produces an excessive die temperature, causing the regulator
to go into thermal shutdown. Internal thermal shutdown
circuitry protects the device from permanent damage.
3) The device is not guaranteed to function outside of its
operating conditions.
4) Measured on JESD51-7, 4-layer PCB.
MP6908A Rev. 1.1
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MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
ELECTRICAL CHARACTERISTICS
VDD = 5V, TJ = -40°C ~ 125°C, unless otherwise noted.
Parameter
Supply Management Section
VDD UVLO rising
VDD UVLO hysteresis
VDD maximum charging
current
Symbol
IVDD
VDD regulation voltage
Operating current
Quiescent current
Shutdown current
Control Circuitry Section
Forward regulation voltage
(VSS - VD)
Turn-on threshold (VDS)
Turn-off threshold (VSS - VD)
Turn-on delay
Turn-off delay
Turn-off propagation delay (5)
Turn-on blanking time
Turn-off blanking threshold
(VDS)
Turn-off threshold during
minimum on time (VDS)
Turn-on slew rate detection
timer
Gate Driver Section
VG (low)
VG (high)
Maximum source current (5)
Maximum sink current (5)
Pull-down impedance
ICC
Iq(VDD)
ISD(VDD)
Conditions
VDD = 7V, HVC = 40V
VDD = 4V, VD = 30V
VD = 12V, HVC = 12V
HVC = 3V, VD = 12V
VDD = 9V, CLOAD = 2.2nF,
FSW = 100kHz
VDD = 5V, CLOAD = 2.2nF,
FSW = 100kHz
VDD = 5V
VDD = UVLO - 0.1V
Vfwd
TDon
TDoff
CLOAD = 2.2nF
CLOAD = 2.2nF
TB-ON
CLOAD = 2.2nF
VB-OFF
Min
Typ
Max
Units
3.55
0.1
35
20
8.5
4.6
3.75
0.2
70
40
9
5
3.95
0.3
110
60
9.5
5.4
V
V
mA
2.9
3.5
mA
1.72
2.1
mA
100
130
100
µA
µA
25
40
55
mV
-115
-6
-57
12
50
45
0.35
-86
3
30
25
15
0.45
0.66
mV
mV
ns
ns
ns
µs
2
2.5
3
V
1.3
1.8
2.1
V
90
115
ns
0.01
0.02
0.5
3
1
2
V
V
A
A
Ω
TSLEW
RSLEW = 400kΩ
65
VG-L
VG-H
ILOAD = 10mA
ILOAD = 0mA
4.9
Same as VG (low)
V
NOTE:
5) Guaranteed by characterization and design.
MP6908A Rev. 1.1
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MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
Operating Current vs. Temperature
Operating Current vs. Temperature
VDD = 9V, CLOAD = 2.2nF, FSW = 100kHz
VDD = 5V, CLOAD = 2.2nF, FSW = 100kHz
3
1.9
2.95
1.85
2.9
1.8
2.85
1.75
ICC(mA)
ICC(mA)
TYPICAL PERFORMANCE CHARACTERISTICS
2.8
2.75
1.7
1.65
2.7
1.6
2.65
1.55
2.6
-50
-25
0
25
50
75
Temperature (°C)
100
1.5
125
-50
Quiescent Current vs. Temperature
108
106
102
TDon(ns)
Iq(µA)
104
100
98
96
94
92
90
125
0
25
50
75
Temperature (°C)
100
125
36
34
32
30
28
26
24
22
20
18
16
14
12
10
-50
Turn-Off Delay vs. Temperature
-25
0
25
50
75
Temperature (°C)
100
125
Forward Regulation Voltage (VSS - VD)
vs. Temperature
VDD = 9V, CLOAD = 2.2nF
36
34
32
30
28
26
24
22
20
18
16
14
12
10
50
48
46
44
Vfwd(mV)
TDoff(ns)
100
VDD = 9V, CLOAD = 2.2nF
110
-25
0
25
50
75
Temperature (°C)
Turn-On Delay vs. Temperature
VDD = 5V
-50
-25
42
40
38
36
34
32
-50
-25
0
25
50
75
Temperature (°C)
100
125
30
-50
-25
0
25
50
75
Temperature (°C)
MP6908A Rev. 1.1
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100
125
5
MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Turn-On Slew Rate Detection Timer
vs. Temperature
VDD Maximum Charging Current vs.
Temperature
RSLEW = 400kΩ
VDD = 4V, VD = 30V
96
94
90
IVDD(mA)
TSLEW(ns)
92
88
86
84
82
80
-50
-25
0
25
50
75
Temperature (°C)
100
125
70
65
60
55
50
45
40
35
30
25
20
15
10
-50
-25
0
25
50
75
Temperature (°C)
100
125
VDD Maximum Charging Current vs.
Temperature
IVDD(mA)
VDD = 7V, HVC = 40V
100
95
90
85
80
75
70
65
60
55
50
45
40
-50
-25
0
25
50
75
Temperature (°C)
100
125
MP6908A Rev. 1.1
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MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Operation in 36W Flyback
Application
Operation in 36W Flyback
Application
VIN = 110VAC, VOUT = 12V, IOUT = 3A,
HVC connected to VD
VIN = 220VAC, VOUT = 12V, IOUT = 3A, HVC
connected to VD
CH1: VDS
20V/div.
CH1: VDS
20V/div.
CH3: VDD
5V/div.
CH3: VDD
5V/div.
CH2: VGS
5V/div.
CH2: VGS
5V/div.
10µs/div.
10µs/div.
Operation in 36W Flyback
Application
Operation in 36W Flyback
Application
VIN = 110VAC, VOUT = 12V, IOUT = 3A, HVC
connected to VSS
VIN = 220VAC, VOUT = 12V, IOUT = 3A, HVC
connected to VSS
CH1: VDS
20V/div.
CH1: VDS
20V/div.
CH3: VDD
5V/div.
CH3: VDD
5V/div.
CH2: VGS
5V/div.
CH2: VGS
5V/div.
10µs/div.
10µs/div.
MP6908A Rev. 1.1
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MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
BLOCK DIAGRAM
VDD Charge
Figure 1: Functional Block Diagram
MP6908A Rev. 1.1
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MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
OPERATION
The
MP6908A
supports
operation
in
discontinuous
conduction
mode
(DCM),
continuous conduction mode (CCM), and quasiresonant flyback converters. The control
circuitry controls the gate in forward mode and
turns the gate off when the synchronous
rectification (SR) MOSFET current drops to
zero.
VDD Generation
The capacitor at VDD supplies power for the IC
and can be charged up by both HVC and VD.
When VHVC < 4.7V, VD charges up the external
capacitor at VDD via a current source with
40mA and regulates it at 5V.
When 4.7V < VHVC < 9.7V, VD stops charging.
HVC charges VDD via a current source with
70mA and regulates it at VHVC - 0.7V.
When VHVC > 9.7V, the HVC charges VDD via a
current source with 70mA and clamps it at 9V.
Start-Up and Under-Voltage Lockout (UVLO)
When VDD rises above 3.75V, the MP6908A
exits under-voltage lockout (UVLO) and is
enabled. The MP6908A enters sleep mode, and
VGS is kept low once VDD drops below 3.55V.
Turn-On Phase
When VDS drops to ~2V, a turn-on timer begins
counting. This turn-on timer can be
programmed by an external resistor on SLEW.
If VDS reaches the -86mV turn-on threshold from
2V within the time set by the timer (TSLEW), the
MOSFET is turned on after a turn-on delay
(around 30ns) (see Figure 2).
If VDS crosses -86mV after the timer ends, the
gate voltage (VG) remains off. This turn-on
timer prevents the MP6908A from turning on
falsely due to ringing from DCM and quasiresonant operations.
TSLEW can be programmed with Equation (1):
TSLEW RSLEW
90ns
400k
(1)
Turn-On Blanking
The control circuitry contains a blanking
function. When the MOSFET turns on, the
control circuit ensures that the on state lasts for
a specific period of time. The turn-on blanking
time is ~450ns to prevent an accidental turn-off
due to the ringing. However, if VDS reaches 2 3V within the turn-on blanking time, VGS is
pulled low immediately.
Conduction Phase
When VDS rises higher than the forward voltage
drop (-40mV) according to the decrease of the
switching current, the MP6908A lowers the gate
voltage level to enlarge the on resistance of the
synchronous MOSFET.
With this control scheme, VDS is adjusted to
around -40mV, even when the current through
the MOSFET is fairly low. This function keeps
the driver voltage at a very low level when the
synchronous MOSFET is turned off, which
boosts the turn-off speed and is especially
important in CCM operation.
Turn-Off Phase
When VDS rises to trigger the turn-off threshold
(-3mV), the gate voltage is pulled to zero after a
very short 25ns turn-off delay (see Figure 2).
Turn-Off Blanking
After the gate driver (VGS) is pulled to zero by
VDS reaching the turn-off threshold (-3mV), a
turn-off blanking time is applied, during which
the gate driver signal is latched off. The turn-off
blanking is removed when VDS rises above 2V
(see Figure 2).
Figure 2: Turn-On/Turn-Off Timing Diagram
MP6908A Rev. 1.1
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MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
APPLICATION INFORMATION
Slew Rate Detection Function
In DCM operation, the demagnetizing ringing
may drop VDS below 0V. If VDS reaches the turnon threshold during the ringing, SR controllers
without the slew rate detection function may
turn on the MOSFET by mistake. Figure 3
shows the waveform of this false turn-on
situation. Not only does this increase power
loss, but may also lead to shoot-through if the
primary-side MOSFET is turned on within the
minimum on time.
External Resistor on VD and HVC
Over-voltage conditions may damage the
device, so application designs must be done
appropriately to guarantee safe operation,
especially on the high-voltage pin.
A common over-voltage condition is when the
body diode of the SR MOSFET is turned on,
and the forward voltage drop may exceed the
negative rating on VD. In this case, place an
external resistor between VD and the drain of
the MOSFET. Generally, the resistance is
recommended to be no less than 300Ω.
Conversely, this resistor cannot be too large,
since a large value compromises the VDD
supply and slows down the VDS detection slew
rate. Generally, it is not recommended to use
any resistance larger than 1kΩ, but for each
practical case, check the resistance based on
the condition of the VDD supply and the slew
rate.
Figure 3: False Turn-On (without Slew Rate
Detection)
Considering that the slew rate of the ringing is
always much less than when the primary
MOSFET is turned off, this false turn-on
situation can be prevented by the slew rate
detection function (see Figure 4). When the
slew rate is less than the threshold set by the
RSLEW, the IC does not turn on the gate, even
when VDS reaches the turn-on threshold.
In applications where HVC may suffer from
negative voltage bias (e.g.: in the high-side setup without auxiliary winding), the same
resistance should be placed on HVC externally.
Typical System Implementations
Figure
5
shows
the
typical
system
implementation for the IC power supply derived
from the output voltage (VOUT), which is
available in low-side rectification.
VD
HVC
MP6908A
SLEW
VDD
VG
VSS
Figure 5: Low-Side Rectification
The MP6908A can support most applications,
even when VOUT is down to 0V for low-side
rectification.
Figure 4: Preventing a False Turn-On (with Slew
Rate Detection)
If the MP6908A is used for high-side
rectification, a self-supply can be achieved
three ways (see Figure 6, Figure 7, and Figure
8).
MP6908A Rev. 1.1
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MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
Figure 6 shows HVC connected to VD. Here,
VDD is generated and regulated at 9V.
Figure 6: High-Side Rectification, VDD Regulated
at 9V
Figure 7 shows HVC connected to the
secondary ground through an external diode.
Here, VDD is generated from HVC and
regulated at 9V. The maximum voltage at HVC
can be calculated with Equation (2):
VHVC(max) VIN
Ns
Np
(2)
SR MOSFET Selection
Power MOSFET selection is a trade-off
between the RDS(ON) and QG. To achieve higher
efficiency, the MOSFET with the smaller RDS(ON)
is preferred. Typically, QG is larger with a
smaller RDS(ON), which makes the turn-on/turnoff speed lower and leads to larger power loss
and driver loss. Because VDS is adjusted at
about -40mV during the driving period when the
switching current is fairly small, a MOSFET with
an RDS(ON) that is too low is not recommended
because the gate driver is pulled low when VDS
= -ISD x RDS(ON) becomes larger than -40mV.
The MOSFET’s RDS(ON) does not contribute to
the conduction loss. The conduction loss is
PCON = -VDS x ISD ≈ ISD x 40mV.
To achieve a fairly high use of the MOSFET’s
RDS(ON), the MOSFET should be turned on
completely for at least 50% of the SR
conduction period. Calculate VDS with Equation
(3):
VDS IC RDS(ON) IOUT / D RDS(ON) Vfwd (3)
VG
VD
MP6908A
VSS
SLEW
HVC
VDD
Figure 7: High-Side Rectification, VDD Regulated
at 9V
Figure 8 shows HVC shorted to VSS. VDD is
generated by VDS and regulated at 5V.
Where VDS is drain-source voltage of the
MOSFET, D is the duty cycle of the secondary
side, IOUT is output current, and Vfwd is the
forward voltage threshold (~40mV).
Figure 9 shows the typical waveform of a
flyback application. Assuming it has a 50% duty
cycle, the MOSFET’s RDS(ON) is recommended
to be no lower than ~20/IOUT (mΩ). For a 5A
application, the RDS(ON) should be no lower than
4mΩ.
Figure 8: High-Side Rectification, VDD Regulated
at 5V
Figure 9: Synchronous Rectification Typical
Waveforms in a Flyback Application
MP6908A Rev. 1.1
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MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
PCB Layout Guidelines
Efficient PCB layout is critical for stable
operation. For best results, refer to Figure 10,
Figure 11, Figure 12, and follow the guidelines
below.
Sensing for VD/VSS
1. Make the sensing connection (VD/VSS) as
close as possible to the MOSFET
(drain/source).
2. Make the sensing loop as small as possible.
3. Keep the IC out of the power loop to prevent
the sensing loop and power loop from
interrupting each other (see Figure 10).
Layout Example
Figure 11 shows a layout example of a single
layer with a through-hole transformer and a
TO220 package SR MOSFET. RSN and CSN
are the R-C snubber network for the SR
MOSFET. The sensing loop (VD and VSS to
the SR MOSFET) is minimized and kept
separate from the power loop. The VDD
decoupling capacitor (C2) is placed beside VDD.
Figure 12 shows another layout example of a
single layer with a Power PAK/SO8 package
SR MOSFET, which also has a minimized
sensing loop and power loop to prevent the
loops from interfering with one another.
6
5
4
1
2
3
Figure 10: Voltage Sensing for VD/VSS
4. Place a decoupling ceramic capacitor from
VDD to PGND close to the IC for adequate
filtering.
Figure 11: Layout Example with TO220 Package
SR MOSFET
Gate Driver Loop
1. Make the gate driver loop as small as
possible
to
minimize
the
parasitic
inductance.
2. Keep the driver signal far away from the VD
sensing trace on the layout.
Figure 12: Layout Example with Power PAK/SO8
SR MOSFET
MP6908A Rev. 1.1
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MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
PACKAGE INFORMATION
TSOT23-6
See note 7
EXAMPLE
TOP MARK
PIN 1 ID
IAAAA
RECOMMENDED LAND PATTERN
TOP VIEW
SEATING PLANE
SEE DETAIL’’A’’
FRONT VIEW
SIDE VIEW
NOTE:
DETAIL "A"
1) ALL DIMENSIONS ARE IN MILLIMETERS
.
2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH
,
PROTRUSION OR GATE BURR.
3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH
OR PROTRUSION.
4) LEAD COPLANARITY(BOTTOM OF LEADS AFTER FORMING)
SHALL BE 0.10 MILLIMETERS MAX.
5) DRAWING CONFORMS TO JEDEC MO-193, VARIATION AB.
6) DRAWING IS NOT TO SCALE.
7) PIN 1 IS LOWER LEFT PIN WHEN READING TOP MARK
FROM LEFT TO RIGHT, (SEE EXAMPLE TOP MARK)
MP6908A Rev. 1.1
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MP6908A – FAST TURN-OFF INTELLIGENT RECTIFIER
Revision History
Revision #
1.1
Revision
Date
Description
05/26/2020 Some min/max specifications are added in the EC table.
Pages
Updated
Page 4
NOTICE: The information in this document is subject to change without notice. Users should warrant and guarantee that third
party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not
assume any legal responsibility for any said applications.
MP6908A Rev. 1.1
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