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LM74670-Q1
SNOSD08A – SEPTEMBER 2015 – REVISED OCTOBER 2015
LM74670-Q1 Zero IQ Smart Diode Rectifier Controller
1 Features
3 Description
•
The LM74670-Q1 is a controller device that can be
used with an N-Channel MOSFET in full or half
bridge rectifier architectures for alternators. It is
designed to drive an external MOSFET to emulate an
ideal diode. A unique advantage of this scheme is
that it is not ground referenced, thus it has zero IQ.
The schottky diodes in full or half bridge rectifiers and
alternators can be replaced with the LM74670-Q1
solution to avoid forward conduction diode losses and
produce more efficient AC-DC converters.
1
•
•
•
•
•
AEC-Q100 Qualified With the Following Results:
– Device Temperature Grade 1: –40°C to
+125°C Ambient Operating Temperature
Range
– Exceeds HBM ESD Classification Level 2
– Device CDM ESD Classification Level C4B
Peak Input AC Voltage: 42 V
Zero IQ
Charge Pump Gate Driver for external N-Channel
MOSFET
Low Forward-Voltage Drop and Less Power
Dissipation Compared to Schottky Diode
Capable of handling AC signal up to 300-Hz
Frequency
Device Information(1)
PART NUMBER
2 Applications
•
•
•
•
The LM74670-Q1 controller provides a gate drive for
external N-Channel MOSFET and a fast response
internal comparator to pull-down the MOSFET Gate
in the event of reverse polarity. This device can
support an AC signal frequency up to 300Hz.
PACKAGE
LM74670-Q1
AC Rectifier
Alternator
Power Tools
Reverse Polarity Protection
VSSOP (8)
BODY SIZE (NOM)
3.00 mm × 5.00 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Smart Diode Full Bridge Rectifier Application
Smart Diode Configuration
Q1
VIN
S
VOUT
D
G
GATE DRIVE
ANODE
0
LM
67
74
67
0
74
LM
AC Input
GATE PULL DOWN
LM74670
VCAPH
CATHODE
VCAPL
0
LM
67
74
67
74
LM
0
VCAP
COUT
LOAD
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM74670-Q1
SNOSD08A – SEPTEMBER 2015 – REVISED OCTOBER 2015
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
4
4
4
4
4
6
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information .................................................
Electrical Characteristics...........................................
Typical Characteristics ..............................................
Detailed Description .............................................. 7
7.1 Overview ................................................................... 7
7.2 Functional Block Diagram ......................................... 7
7.3 Feature Description .................................................. 7
7.4 Device Functional Modes........................................ 10
8
Application and Implementation ........................ 12
8.1 Typical Rectifier Application ................................... 12
8.2 Design Requirements.............................................. 16
9 Power Supply Recommendations...................... 17
10 Layout................................................................... 17
10.1 Layout Guidelines ................................................. 17
10.2 Layout Example .................................................... 18
11 Device and Documentation Support ................. 19
11.1
11.2
11.3
11.4
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
19
19
19
19
12 Mechanical, Packaging, and Orderable
Information ........................................................... 19
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Original (September 2015) to Revision A
•
2
Page
Product Preview to Production Data ..................................................................................................................................... 1
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SNOSD08A – SEPTEMBER 2015 – REVISED OCTOBER 2015
5 Pin Configuration and Functions
DGK Package
8-Pin VSSOP
Top View
VCAPL
1
8
Cathode
Gate Pull Down
2
7
VCAPH
LM74670-Q1
NC
3
6
Gate Drive
Anode
4
5
NC
Pin Functions
PIN NO.
NAME
I/O
1
VcapL
Charge Pump Output, connect to an external charge pump capacitor
DESCRIPTION
2
Gate Pull Down
Connect to the gate of the external MOSFET for fast turn OFF in the case of
reverse polarity
3
NC
No connect. Leave floating or connect to Anode pin
4
Anode
Anode of the diode, connect to source of the external MOSFET
5
NC
No connect. Leave floating or connect to gate drive pin
6
Gate Drive
Gate Drive output, Connect to the Gate of the external MOSFET
7
VcapH
Charge Pump Output, connect to an external charge pump capacitor
8
Cathode
Cathode of the diode, connect to Drain of the external MOSFET
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)
Cathode to Anode (For a 2ms time duration)
Cathode to Anode (Continuous)
(1)
(2) (3)
,
(3)
MIN
MAX
UNIT
-3
45
V
-3
42
V
VcapH to VcapL
-0.3
7
V
Anode to VcapL
-0.3
3
V
Gate Drive, Gate Pull Down to VcapL
-0.3
7
V
-40
125
°C
Case Temperature (TC-MAX)
-40
125
°C
Storage temperature range, Tstg
-65
150
°C
Ambient Temperature (TA-MAX)
(1)
(2)
(3)
(4)
(4)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
42V continuous (and 45V transients for 2ms) absmax condition from Cathode to Anode. Suitable to use with TVS SMBJ28A and
SMBJ14A at the anode.
Reverse voltage rating only. There is no positive voltage limitation for the LM74670-Q1 Anode terminal.
The device performance is ensured over this Ambient Temperature range as long the Case Temperature does not exceed the MAX
value.
6.2 ESD Ratings
VALUE
Electrostatic discharge (1)
V(ESD)
(1)
(2)
Human body model (HBM), per AEC Q100-002 (2)
±4000
Charged-device model (CDM), per AEC Q100-011
±750
UNIT
V
AEC Q100-002 indicates that HBM stressing shall be in accordance with the ANSI/ESDA/JEDEC JS-001 specification.
The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
NOM
MAX
Cathode To Anode
Ambient Temperature (TA-MAX)
-40
Case Temperature (TC-MAX)
UNIT
42
V
125
°C
125
°C
6.4 Thermal Information
LM74670-Q1
THERMAL METRIC (1)
DGK (VSSOP)
UNIT
8 PINS
RθJA
Junction-to-ambient thermal resistance
RθJC(top)
Junction-to-case (top) thermal resistance
73
RθJB
Junction-to-board thermal resistance
102
ψJT
Junction-to-top characterization parameter
11
ψJB
Junction-to-board characterization parameter
100
(1)
181
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953
6.5 Electrical Characteristics
(1)
TA= 25°C unless otherwise noted. Minimum and Maximum limits are specified through test, design, validation or statistical
correlation. Typical values represent the most likely parametric norm at TA= 25°C and are provided for reference purpose
(1)
4
Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which
operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits
and associated test conditions, see the table of Electrical Characteristics.
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Electrical Characteristics (continued)
(1)
TA= 25°C unless otherwise noted. Minimum and Maximum limits are specified through test, design, validation or statistical
correlation. Typical values represent the most likely parametric norm at TA= 25°C and are provided for reference purpose
only. VAnode-Cathode= 0.55V for all tests.
only. VAnode-Cathode= 0.55V for all tests.
PARAMETER
TEST CONDITIONS
MIN
VAnode to Cathode
Minimum Startup Voltage across
External MOSFET's Body Diode
External MOSFET VGS = 0V
0.48
VcapThreshold
Charge Pump Capacitor Drive
Thresholds
Vcap Upper Threshold
5.15
V
IGate
up
Gate Drive Pull up current
VGate to Anode = 2V
60
67
µA
IGate
down
Gate Drive pull down current
during forward voltage
VGate to Anode = 4V
55
62
µA
IGate pull down
Gate drive pull down current
when reverse voltage is sensed
VGate Pull Down = VAnode + 2V
160
mA
ICharge
Charging current for the charge
pump capacitor
VAnode to Cathode = 0.55 V
46
µA
IDischarge
VCAP Current Consumption to
power the controller when
MOSFET is ON
Vcap = 6.6V
0.95
µA
TRecovery
Time to shut off MOSFET when
VAnode to Cathode = -20 mV
voltage is reversed (Equivalent to Cgate = 4 nF
diode reverse recovery time)
D
Duty Cycle
ILKG
Reverse Leakage Current
Iq
Quiescent Current to GND
IAnode
Current into Anode pin
MAX
V
6.3
Vcap Lower Threshold
UNIT
40
2.2
Iload = 3 A, TA = 25°C
98%
Iload = 3 A, TA = 125°C
92%
VAnode to Cathode = -13.5 V
60
Current into Anode pin when VAnode Cathode = 0.3V.
V
5 (2)
µs
110 (2)
µA
0
µA
30
µA
Limit applies over the full Operating Temperature Range TA = -40°C to +125°C.
VANODE ± VCATHODE
(2)
TYP
30 mV
0 mV
-20 mV
VANODE > VCATHODE
VCATHODE > VANODE
tTRECOVERYt
VGATE ± VANODE
VGATE
0V
Figure 1. Gate Shut Down Timing in the Event of Reverse Polarity
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6.6 Typical Characteristics
300
0.465
Anode to Cathode Voltage (V)
V_Reverse = 13.5 V
V_Reverse = 37 V
Leakage Current (PA)
250
200
150
100
50
-40
-20
0
20
40
60
80
Temperature (qC)
100
120
0.46
0.455
0.45
0.445
0.44
0.435
-40
140
Figure 2. Reverse Leakage at Negative Voltages
0
20
40
60
80
Temperature (qC)
100
120
140
D002
Figure 3. Anode to Cathode Startup Voltage
3.25
Vcap High and Low Voltage (V)
6.5
3
Trecovery (µs)
-20
D001
2.75
2.5
2.25
2
-40
-20
0
20
40
60
80
Temperature (°C)
100
120
VCAP H
VCAP L
6.25
6
5.75
5.5
5.25
5
-40
140
-20
0
20
D009
Figure 4. Reverse Recovery Time (TRecovery)
40
60
80
Temperature (qC)
100
120
140
D003
Figure 5. VcapH and VcapL Voltage Threshold
100
100
90
80
70
Duty Cycle (%)
Duty Cycle (%)
80
60
50
40
30
-40qC
25qC
85qC
125qC
20
10
40
20
-40qC
25qC
85qC
125qC
0
0
-20
0
0.1
0.2
0.3
0.4 0.5 0.6
Current (A)
0.7
0.8
0.9
1
0
1
D005
Figure 6. Duty Cycle of the Output Voltage at Startup
6
60
2
3
4
5
6
Current (A)
7
8
9
10
D004
Figure 7. Duty Cycle of the Output Voltage
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7 Detailed Description
7.1 Overview
Using N-Channel MOSFETs with controller ICs can be highly effective and more efficient substitutes of lossy
diodes in a bridge rectifier application. The LM74670-Q1 is designed to control a single N-Channel MOSFET in a
full or half bridge rectifier as replacement for diode. In a full bridge rectifier, each diode can be replaced by the
LM74670-Q1 and a MOSFET. Diodes used in bridge rectifiers cause high power losses associated with the
forward voltage drop of each diode. In each cycle of sinusoidal AC voltage, two diodes conduct at the same time.
Power losses during diode forward conduction increase as the output current increases. Diode rectification also
increases peak current for applications that require high value output capacitance due to charge and discharge
with the diode drop voltage. The ON state forward voltage loss in a MOSFET depends upon the RDSON of the
MOSFET. The power losses become substantially lower than diodes for the equivalent current. This solution has
a small increase in complexity; however it eliminates the need for diode heatsinks and thermal management for
high power AC bridge rectifier applications.
The LM74670-Q1 is a zero Iq controller that is combined with an external N-channel MOSFET to replace each
diode in a bridge rectifier. The voltage across the MOSFET source and drain is constantly monitored by the
LM74670-Q1 Anode and Cathode pins. An internal charge pump is used to provide the GATE drive for the
external MOSFET. The forward conduction is through the MOSFET 98% of the time. The forward conduction is
through the MOSFET body diode for 2% of time when energy is stored in an external charge pump capacitor
Vcap Figure 9. This stored energy is used to drive the gate of MOSFET. The voltage drop and power losses
depend on the RDSONof MOSFETs used to replace the rectifier diodes. The LM74670-Q1 has no ground
reference which makes it identical to a diode.
7.2 Functional Block Diagram
Input
S
Output
D
G
ANODE
GATE DRIVE
GATE PULL DOWN
CATHODE
11.5 V
VCAPL
LOGIC
VCAPH
Charge
Pump
Reverse Batt
Shut Off
7.3 Feature Description
7.3.1 During T0
When power is initially applied, the load current (ID) will flow through the body diode of the MOSFET and produce
a voltage drop (Vf) during T0 in Figure 8. This forward voltage drop (Vf) across the body diode of the MOSFET is
used to charge up the charge pump capacitor Vcap. During this time, the charge pump capacitor Vcap is
charged to a higher threshold of 6.3V (typical).
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Feature Description (continued)
VOUT
Body Diode Voltage Drop
T0
tT1t
FET is ON
VGS
FET is OFF
0V
Figure 8. Output Voltage and VGSOperation at 1A Output Current
7.3.2 During T1
Once the voltage on the capacitor reaches a higher voltage level of 6.3V (typical), the charge pump is disabled
and the MOSFET turns ON. The energy stored in the capacitor is used to provide the gate drive for the MOSFET
(T1 in Figure 8). When the MOSFET is ON, it provides a low resistive path for the drain current to flow and
minimizes the power dissipation associated with forward conduction. The power losses during the MOSFET ON
state depend primarily on the RDSON of the selected MOSFET and load current. At time when the capacitor
voltage reaches its lower threshold VcapL 5.15V (typical), the MOSFET gate turns OFF. The drain current ID will
then begin to flow through the body diode of the MOSFET, causing the MOSFET body diode voltage drop to
appear across Anode and Cathode pins. The charge pump circuitry is re-activated and begins charging the Vcap.
The LM74670-Q1 operation keeps the MOSFET ON at approximately 98% duty cycle (typical) regardless of the
external charge pump capacitor value. This is the key factor to minimizing the power losses. The forward voltage
drop during this time is limited by the RDSON of the MOSFET.
7.3.3 Pin Operation
7.3.3.1 Anode and Cathode Pins
The LM74670-Q1 Anode and Cathode pins are connected to the source and drain of the external MOSFET. The
current into the Anode pin is 30 µA (typical). When power is initially applied, the load current flows through the
body diode of the external MOSFET, the voltage across Anode and Cathode pins is equal to the forward diode
drop . The minimum value of diode voltage drop required to enable the charge pump circuitry is 0.48V. Once the
MOSFET is turned ON, the Anode and Cathode pins constantly sense the voltage difference across the
MOSFET to determine the magnitude and polarity of the voltage across it. When the MOSFET is on, the voltage
difference across Anode and Cathode pins depends on the RDSON and load current. If voltage difference across
source and drain of the external MOSFET becomes negative, this is sensed as a fault condition by Anode and
Cathode pins and gate is turned off by Gate Pull Down pin as shown in Figure 1. The reverse voltage threshold
across Anode and Cathode to detect the fault condition is -20 mV. The consistent sensing of voltage polarity
across the MOSFET enables the LM74670-Q1 to provide a fast response to the power source failure and limit
the amount and duration of the reverse current flow.
7.3.3.2 VcapH and VcapL Pins
VcapH and VcapL are high and low voltage thresholds respectively that the LM74670-Q1 uses to detect when to
turn the charge pump circuitry ON and OFF. The capacitor charging and discharging time can be correlated to
the duty cycle of the MOSFET gate. Figure 9 shows the voltage behavior across the Vcap. During the time
period T0, the capacitor is storing energy from the charge pump. The MOSFET is turned off and current flow is
only through the body diode during this time period. The conduction though body diode of the MOSFET is for a
8
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Feature Description (continued)
very small period of time (2% typical) which rules out the chances of overheating the MOSFET, regardless of the
output current. Once the capacitor voltage reaches its high threshold, the MOSFET is turned off and charge
pump circuity is deactivated until the Vcap reaches its low voltage threshold (T1). The voltage difference between
Vcap high and low threshold is typically 1.15V. The LM74670-Q1 charge pump has 46µA charging capability with
5-8MHz frequency.
VCAPH
1.1 V
VCAPL
VOUT
Body Diode Voltage Drop
T0
tT1t
Figure 9. Vcap Charging and Discarding by the Charge Pump
The Vcap current consumption is 0.95µA (typical) to drive the gate. The MOSFET OFF time (T0) and ON time
(T1) can be calculated using the following expression
dV
'T C
dI
(1)
Where:
• C = Vcap Capacitance
• dV = 1.15V
• dI = 46 µA for charging
• dI = 0.95 µA for discharging
Note: Temperature dependence of these parameters – The duty cycle is dependent on temperature since the
capacitance variation over temperature has a direct correlation to the MOSFET OFF and ON periods and the
frequency. If the capacitor varies 20% the periods and the frequency will also vary by 20% so it is recommended
to use a quality X7R/COG cap and not to place the cap in close proximity to high temperature devices. The
variation of the capacitor does not have a thermal impact in the application as the duty cycle does not change.
7.3.3.3 Gate Drive Pin
When the charge pump capacitor is charged to the high voltage level of 6.3V (typ), the Gate Drive pin provides a
67µA (typ) of drive current. When the charge pump capacitor reaches its lower voltage threshold of 5.15V (typ),
Gate is pulled down to the Anode voltage (Vin). During the positive cycle of AC sinusoid, the MOSFET gate is
turned ON by the LM74670-Q1 gate drive to ensure the forward conduction through the MOSFET.
7.3.3.4 Gate Pull Down Pin
The Gate Pull Down pin of the LM74670-Q1 is connected to the Gate Drive pin in a bridge rectifier application.
When the controller detects negative polarity during the negative cycle of AC sinusoidal, the Pull-Down quickly
discharges the MOSFET gate through a discharge transistor. This fast pull down reacts regardless of the Vcap
charge level. When the negative voltage across the Anode and Cathode pins due to reverse current reaches
-20mV (typical), the LM74670-Q1 immediately reacts and discharges the MOSFET gate capacitance as shown in
Figure 10 . The Gate voltage is pulled down to Anode voltage with 160mA pull down current when the negative
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Feature Description (continued)
cycle of the AC input starts. . A MOSFET with 4nF of effective gate capacitance can be turned off by the
LM74670-Q1 within 2.2µs (typical). The fast turnoff time minimizes the reverse current flow from MOSFET drain
by opening the circuit. The reverse leakage current does not exceed 110µA for a constant 13.5V reverse voltage
across Anode and Cathode pins. The reverse leakage current for a Schottky diode is 15mA under the same
voltage and temperature conditions.
Figure 10. Gate Pull Down in the Event of Reverse Polarity
7.4 Device Functional Modes
The LM74670-Q1 operates in two modes:
• Body Diode Conduction Mode
The LM74670-Q1 solution works like a conventional diode during this time with higher forward voltage drop.
The power dissipation during this time can be given as:
PDissipation
VForward Drop u IDrain Current
(2)
However, the current only flows through the body diode while the MOSFET gate is being charged to VGS(TH).
This conduction is only for 2% duty cycle, therefore it does not cause any thermal issues.
Body Diode ON Time
•
10
C u (VcapH VcapL)
ICharge Current
(3)
The MOSFET Conduction Mode
The MOSFET is turned on during this time and current flow is only through the MOSFET. The forward voltage
drop and power losses are limited by the RDSON of the specific MOSFET used in the solution. The LM74670Q1 solution output is comprised of the MOSFET conduction mode for 98% of its duty cycle. This time period
is given by the following expression:
C u (VcapH VcapL)
MOSFET ON Time
IDischarge Current
(4)
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Device Functional Modes (continued)
7.4.1 Duty Cycle Calculation
The LM74670-Q1 has an operating duty cycle of 98% at 25 ̊C and >90% at 125 ̊C. The duty cycle doesn’t
depend on the Vcap capacitance value. However, the variation in capacitance value over temperature has direct
correlation to the switching frequency between the MOSFET and body diode. If the capacitance value decreases,
the charging and discharging time will also decrease, causing more frequent switching between body diode and
the MOSFET condition. The following expression can be used to calculate the duty cycle of the LM74670-Q1:
Duty Cycle (%)
(MOSFET ON Time)
u 100
(MOSFET ON Time Body Diode ON Time)
(5)
7.4.2 Startup Voltage
The LM74670-Q1 will not initiate the charge pump operation if a closed loop system is in standby mode or the
drain current is smaller than 1mA (typical). This is due to a minimum body diode voltage requirement of the
LM74670-Q1 controller. If the drain current is too small to produce a minimum voltage drop of 0.48V at 25 ͦC, the
charge pump circuitry will remain off and the MOSFET will act just like a diode. It is very important to know the
body diode voltage parameter of a MOSFET before implementing it into the Smart Diode solution. Some Nchannels MOSFETs have very low body diode voltage at higher temperature. This makes their drain current
requirement higher to achieve 0.48V across the body diode in order to initiate the LM74670-Q1 controller at
higher temperatures.
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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 should
validate and test their design implementation to confirm system functionality.
8.1 Typical Rectifier Application
The LM74670-Q1 can be used with appropriate N-channel MOSFET to replace a diode in a typical rectifier
application. The rectifier could be industrial for a 12/24AC supply or an automotive rectifier for a single phase or
three phase field winding controlled alternator. The schematic for a typical implementation is shown in Figure 11
to implement a full bridge rectifier. The same schematic can also be extended to six legs for a three phase
alternator rectification. Following considerations need to be made when selecting the appropriate MOSFET for
this application:
1. An input voltage of 24V AC can reach a 34V peak. The MOSFET selected should have a VDS greater than
this voltage.
2. The Continuous drain current of the MOSFET should be nearly 2.5X IAVG to cover peak currents during
rectification.
3. The VGS(TH) threshold voltage of the selected MOSFET should be ≤3V to ensure error-free operation.
+OUT
Q2
LM74670-Q1
VCAPL
Q3
VCAPH
LM74670-Q1
VCAPL
1 µF
VCAPH
1 µF
IN~
IN~
Q1
LM74670-Q1
VCAPL
Q4
VCAPH
1 µF
LM74670-Q1
VCAPL
VCAPH
1 µF
±OUT
Figure 11. Typical Full Bridge Rectifier Application
12
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Typical Rectifier Application (continued)
8.1.1 Design Requirements
For this design example, use the parameters listed in Table 1 as the input parameters
Table 1. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input Voltage Range
4 – 42V peak AC
Output Voltage
rectified positive amplitude
Output current range
Maximum Drain current of MOSFET
Threshold voltage of FET VGS(TH)
3V Max
Vcap value
1µF
8.1.2 Detailed Design Procedure
To begin the design process, determine the following:
8.1.2.1 Design Considerations
• Input voltage range
• Output current range
• Body Diode forward voltage drop for the selected MOSFET
• MOSFET Gate threshold voltage
8.1.2.2 Capacitor Selection
A ceramic capacitor should be placed between VcapL and VcapH. The capacitor acts as a holding tank to power
up the control circuitry when the MOSFET is on.
When the MOSFET is off, this capacitor is charged up to higher voltage threshold of ~6.3V. Once this voltage is
reached, the Gate Drive of LM74670-Q1 will provide drive for the external MOSFET. When the MOSFET is ON,
the voltage across its body diode is collapsed because the forward conduction is through the MOSFET. During
this time, the capacitor acts as a supply for the Gate Drive to keep the MOSFET ON.
The capacitor voltage will gradually decay when the MOSFET is ON. Once the capacitor voltage reaches a lower
voltage threshold of 5.15V, the MOSFET is turned off and the capacitor gets recharged again for the next cycle.
A capacitor value of 220nF to 2.2uF with X7R/COG characteristic and 16V rating or higher is recommended for
this application. A higher value capacitor sets longer MOSFET ON time and OFF time; however, the duty cycle
remains at ~98% for MOSFET ON time irrespective of capacitor value.
If the Vcap value is 1µF, the MOSFET ON time and OFF time can be calculated using Equation 1 :
MOSFET ON Time = (1µF x 1.15V)/0.95µA = 1.21 seconds
Body Diode ON Time = (1µF x 1.15V)/46µA = 25 miliseconds
(6)
(7)
The duty cycle can be calculated using Equation 5 :
Duty Cycle % = 1.21 sec / (1.21 sec + 0.025sec) = 98%
(8)
8.1.2.3 MOSFET Selection
The important MOSFET electrical parameters are the maximum continuous Drain current ID, the maximum drainto-source voltage VDS(MAX), the gate-to-source threshold voltage VGS(TH) and the drain-to-source On resistance
RDSON. The maximum continuous drain current, ID, rating must exceed the maximum continuous load current.
The rating for the maximum current through the body diode, IS, is typically rated the same as, or slightly higher
than the drain current, but body diode current only flows for a small period while the MOSFET gate is being
charged to VGS(TH).The LM74670-Q1 can provide up to 5V VGS to drive the external MOSFET, therefore the VGS
threshold of the selected MOSFET must be ≤ 3V.
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The voltage across the MOSFET's body diode must be higher than 0.48V at low current. The body diode voltage
for MOFETS typically decreases as the ambient temperature increases. This will increase the source current
requirement to achieve the minimum body diode drain-to-source voltage for the charge pump to initiate. The
maximum drain-to-source voltage, VDS(MAX), must be high enough to withstand the highest differential voltage
seen in the application. This would include any anticipated fault conditions. Although there are no positive VDS
limitation. However, it is recommended to use MOSFETS with voltage rating up to 45V for automotive
applications, since the LM74670-Q1 has a reverse voltage limit of -45V. Table 2 shows the examples of
recommended MOSFETs to be used with the LM74670-Q1.
8.1.3 Application Curves
In the following plots, the input voltage is 20V AC. The output current is 5A for all frequencies.
VIN (5 V/DIV)
VGS of Q1 (5 V/DIV)
VOUT (5 V/DIV)
Time (5 ms/DIV)
Figure 12. Response to 60Hz AC Input
VIN (5 V/DIV)
VGS of Q1 (5 V/DIV)
VOUT (5 V/DIV)
Time (5 ms/DIV)
Figure 13. Response to 100Hz AC Input
14
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VIN (5 V/DIV)
VGS of Q1 (5 V/DIV)
VOUT (5 V/DIV)
Time (2 ms/DIV)
Figure 14. Response to a 300Hz AC Input
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8.2 Design Requirements
NOTE
Startup voltage is the voltage drop is needed for the controller to turn ON. It directly
influences the Minimum output current at which the MOSFET turns ON.
Table 2. Recommended MOSFET Examples (1)
Rdson
mΩ @ 4.5V
Vgs
Threshold
(V)
Diode
Voltage
@ 2A at
125C/175C
5
26
1.8
60
5.5
2.5
29
5.6
23.5
6
12
40
Part No
Voltage
(V)
Current
CSD17313Q2Q1
30
SQJ886EP
40
SQ4184EY
40
Si4122DY
40
RS1G120MN
40
RS1G300GN
Drain
Current
at 25C
Package; Footprint
Qual
0.65
SON; 2 x 2
Auto
0.5
PowerPAK SO-8L; 5 x 6
Auto
2.5
0.5
SO-8; 5 x 6
Auto
2.5
0.5
SO-8; 5 x 6
Auto
20.7
2.5
0.6
HSOP8; 5 x 6
Auto
30
2.5
2.5
0.5
HSOP8; 5 x 6
Auto
CSD18501Q5A
40
22
3.3
2.3
0.53
SON; 5 x 6
Industrial
SQD40N06-14L
60
40
17
2.5
0.5
TO-252; 6 x 10
Auto
SQ4850EY
60
12
31
2.5
0.55
SO-8; 5 x 6
Auto
CSD18532Q5B
60
23
3.3
2.2
0.53
SON;5 x 6
Industrial
IPG20N04S4L-07A
40
20
7.2
2.2
0.48
PG-TDSON-8-10; 5 x 6
Auto
IPB057N06N
60
45
5.7
3.3
0.55
PG-TO263-3; 10 x 15
Auto
IPD50N04S4L
40
50
7.3
2.2
0.50
PG-TO252-3-313; 6 x10
Auto
Auto
(1)
16
BUK9Y3R5-40E
40
100
3.8
2.1
0.48
LFPAK56; Power-SO8
(SOT669); 5 x 6
IRF7478PbF-1
60
7
30
3
0.55
SO-8; 5 x 6
Industrial
SQJ422EP
40
75
4.3
2.5
0.50
PowerPAK SO-8L; 5 x 6
Auto
IRL1004
40
130
6.5
1
0.60
TO-220AB
Auto
AUIRL7736
40
112
2.2
3
0.65
DirectFET®; 5 x 6
Auto
The LM74670-Q1 solution is not limited to the MOSFETs included in this table. It only shows examples of compatible MOSFETs.
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9 Power Supply Recommendations
While testing the LM74670-Q1 solution, it is important to use low impedance power supply which allows current
sinking. If the power supply does not allow current sinking, it would prevent the current flow in the reverse
direction in the event of reverse polarity. The MOSFET gate won't get pulled down immediately due to the
absence of reverse current flow.
10 Layout
10.1 Layout Guidelines
•
•
•
•
•
•
•
•
The VIN terminal is recommended to have a low-ESR ceramic bypass-capacitor. The typical recommended
bypass capacitance is a 10-μF ceramic capacitor with a X5R or X7R dielectric.
The VIN terminal must be tied to the source of the MOSFET using a thick trace or polygon.
The Anode pin of the LM74670-Q1 is connected to the Source of the MOSFET for sensing.
The Cathode pin of the LM74670-Q1 is connected to the drain of the MOSFET for sensing.
The high current path of for this solution is through the MOSFET, therefor it is important to use thick traces for
source and drain of the MOSFET.
The charge pump capacitor Vcap must be kept away from the MOSFET to lower the thermal effects on the
capacitance value.
The Gate Drive and Gate pull down pins of the LM74670-Q1 must be connected to the MOSFET gate without
using vias.
Obtaining acceptable performance with alternate layout schemes is possible, however this layout has been
shown to produce good results and is intended as a guideline.
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10.2 Layout Example
1. VcapL
2. PullDown
3. NC
4. Anode
8. Cathode
7. VcapH
6. Gate Drive
5. NC
Figure 15. Layout Example
18
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11 Device and Documentation Support
11.1 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.2 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.3 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.4 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM74670QDGKRQ1
ACTIVE
VSSOP
DGK
8
2500
RoHS & Green
NIPDAUAG
Level-2-260C-1 YEAR
-40 to 125
ZGPK
LM74670QDGKTQ1
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
NIPDAUAG
Level-2-260C-1 YEAR
-40 to 125
ZGPK
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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