TPS2419
SLVS998B – FEBRUARY 2010 – REVISED SEPTEMBER 2011
www.ti.com
N+1 and ORing Power Rail Controller with Enable
Check for Samples: TPS2419
FEATURES
1
•
•
•
•
•
•
•
•
•
Control External FET for N+1 and ORing
Controls Buses From 3 V to 16.5 V
External Enable
N-Channel MOSFETControl
Rapid Device Turnoff Protects Bus Integrity
Programmable Turn-Off Threshold
Soft Turn on Reduces Bus Transients
Industrial Temperature Range: –40°C to 85°C
8-Pin TSSOP and SOIC Packages
APPLICATIONS
•
•
•
•
N+1 Power Supplies
Server Blades
Telecom Systems
High Availability Power Modules
DESCRIPTION
The TPS2419 controller, in conjunction with an
external N-channel MOSFET, provides the reverse
current protection of an ORing diode with the
efficiency of a MOSFET. The TPS2419 can be used
to combine multiple power supplies to a common bus
in an N+1 configuration, or to combine redundant
input power buses.
Applications for the TPS2419 include a wide range of
systems including servers and telecom. These
applications often have either N+1 redundant power
supplies, redundant power buses, or both. Redundant
power sources must have the equivalent of a diode
OR to prevent reverse current during faults and
hotplug.
Accurate voltage sensing and a programmable
turn-off threshold allows operation to be tailored for a
wide
range
of
implementations
and
bus
characteristics. The TPS2419 brings out an enable
pin which allows the system to force the MOSFET off
under light-load, high noise conditions.
Table 1. Family Features
C
GATE
RSVD
GND
R2
RSET
EN
Common Voltage Rail
CBYP
BYP
A
R1
Voltage Source
Enable
'2410
'2411
Enable input
√
√
Linear gate control
√
'2412
'2419
√
√
√
ON/OFF gate
control
'2413
RSET
Turnoff
comparator
filtering
√
√
Voltage monitoring
√
√
MOSFET fault
monitoring
√
√
Status pin
√
√
Independent
Supply Pin
√
√
√
√
√
√
Figure 1. Typical Application
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2010–2011, Texas Instruments Incorporated
TPS2419
SLVS998B – FEBRUARY 2010 – REVISED SEPTEMBER 2011
www.ti.com
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
PRODUCT INFORMATION (1)
(1)
DEVICE
TEMPERATURE
TPS2419
–40°C to 85°C
PACKAGE (1)
MOSFET GATE
CONTROL
PW (TSSOP-8)
ON/OFF
D (SO-8)
MARKING
2419
2419D
For package and ordering information, see the Package Option Addendum at the end of this
document, or see the TI Web site at www.ti.com.
ABSOLUTE MAXIMUM RATINGS (1)
over recommended operating junction temperature range, voltages are referenced to GND (unless otherwise noted)
A, C voltage
A above C voltage
C above A voltage
V
V
BYP to A voltage
–0.3 to 13
V
GATE short to A or C or GND
(2)
V
18
EN
(1)
V
7.5
–0.3 to 30
RSET (2) voltage
TJ
UNIT
GATE, BYP voltage (2)
GATE above BYP voltage
ESD
VALUE
–0.3 to 18
0.3
V
–0.3 to 7
V
–0.3 to 5.5
V
Indefinite
Human body model
2
Charged device model
Maximum junction temperature
kV
500
V
Internally limited
°C
Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings
only and functional operation of the device at these or any other conditions beyond those indicated under recommended operating
conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Voltage should not be applied to these pins.
DISSIPATION RATINGS
θJA – High k °C/W
POWER RATING
High k
TA = 85°C (mW)
258
159
250
176
97.5
410
PACKAGE
θJA – Low k °C/W
PW (TSSOP)
D (SO)
2
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RECOMMENDED OPERATING CONDITIONS
voltages are referenced to GND (unless otherwise noted)
MIN
(1)
NOM
UNIT
16.5
V
5
V
A, C
Input voltage range
A to C
Operational voltage
EN
Input voltage range
0
5
V
R(RSET)
Resistance range (2)
1.5
∞
kΩ
C(BYP)
Capacitance Range (2)
800
10k
pF
TJ
Operating junction temperature
–40
125
°C
(1)
(2)
0
MAX
2200
V(C) must exceed 2.5 V for normal operation and 3 V to meet gate drive specification
Voltage should not be applied to these pins.
ELECTRICAL CHARACTERISTICS (1)
Common conditions (unless otherwise noted) are: [3 V ≤ ( V(A), V(C) ) ≤ 18 V ] , C(BYP) = 2200 pF, R(RSET) = open, EN = 2 V,
GATE = open, –40°C ≤ TJ ≤ 125°C, positive currents into pins, typical values are at 25°C, all voltages with respect to GND.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
A, C
Supply UVLO
A current
C current
V(C) rising
2.25
2.5
Hysteresis
0.25
| I(A) |, Gate in active region
0.66
| I(A) |, Gate saturated high
0.1
Worst case, gate in active region, V(AC) ≤ 0.1 V
4.25
Gate saturated high, V(AC) ≤ 0.1 V
1
6
1.2
V
mA
mA
EN
Threshold voltage
V(EN) rising
1.25
Hysteresis
Response time
Leakage current (source or sink)
1.3
1.35
29
V
mV
V(AC) = 0.1 V, V(EN)↑ : 1.1 V → 1.4 V, measure
period to V(GATE) = 0.25 V
0.65
1
V(AC) = 0.1 V, V(EN)↓: 1.4 V → 1.1 V, measure
period to V(GATE) = V(ON) - 0.25 V
0.3
0.6
μs
V(EN) = 0.5 V
1
μA
71
mV
TURN ON
Forward turn-on voltage - VON
V(A-C)
58
65
TURN OFF
Gate sinks > 10 mA at V(GATE-A) = 2 V
Turn-off threshold voltage
V(A-C) falling, R(RSET) = open
1
3
5
V(A-C) falling, R(RSET) = 28.7 kΩ
-17
-13.25
-10
V(A-C) falling, R(RSET) = 3.24 kΩ
-170
-142
-114
Turn-off delay
V(A) = 12 V, V(A-C): 20 mV → –20 mV,
V(GATE-A) begins to decrease
Turn-off time
V(A) = 12 V, C(GATE-GND) = 0.01 μF, V(A-C):
20 mV → –20 mV, measure the period to
V(GATE) = V(A)
(1)
mV
70
ns
130
ns
Parameters with only typical values are provided for reference only, and do not constitute part of TI's published device specifications for
purposes of TI's product warranty.
3
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SLVS998B – FEBRUARY 2010 – REVISED SEPTEMBER 2011
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ELECTRICAL CHARACTERISTICS(1) (continued)
Common conditions (unless otherwise noted) are: [3 V ≤ ( V(A), V(C) ) ≤ 18 V ] , C(BYP) = 2200 pF, R(RSET) = open, EN = 2 V,
GATE = open, –40°C ≤ TJ ≤ 125°C, positive currents into pins, typical values are at 25°C, all voltages with respect to GND.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
GATE
Gate positive drive voltage, V(GATE-A)
Gate source current
V(C) = 3 V, V(A-C) = 200 mV
6
7
8
5 V ≤ VC ≤ 18 V, V(A-C) = 200 mV
9
10.2
11.5
250
290
350
V(GATE) = 8 V
1.75
2.35
V(GATE) = 5 V
1.25
1.75
Period
7.5
12.5
μs
V(A-C) = –0.1 V, 3 V ≤ VC ≤ 18 V,
2 V ≤ V(GATE) ≤ 18 V
15
19.5
mA
135
°C
10
°C
V(A-C) = 200 mV, V(GATE-A) = 4 V
V
μA
V(A-C) = –0.1 V
Turn-off pulsed current, I(GATE)
Sustain turn-off current, I(GATE)
A
MISCELLANEOUS
Thermal shutdown temperature
Temperature rising, TJ
Thermal hysteresis
+
-
FUNCTIONAL BLOCK DIAGRAM
VDD
10V
Charge Pump
and Bias Supply
HVUV
BYP
TURNON
COMP.
S Q
R Q
+
A
+
-
VON
C
0.5V
+ 3mV
-
RSET
VDD
A
-
TURNOFF en
COMP.
GATE
en
+
Thermal Shutdown en
(135ºC)
C
1.3V
MULTISTAGE
PULLDOWN
EN
RSVD
GND
VDD
Bias and
Control
VBIAS
en
HVUV
4
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TPS2419
SLVS998B – FEBRUARY 2010 – REVISED SEPTEMBER 2011
www.ti.com
PW and D PACKAGE
(TOP VIEW)
1
4
RSET
EN
RSVD
GND
BYP
A
C
GATE
8
5
TERMINAL FUNCTIONS
TERMINAL
I/O
DESCRIPTION
NAME
NO.
RSET
1
I
Connect a resistor to ground to program the turn-off threshold. Leaving RSET open results in a slightly
positive V(A-C) turn-off threshold.
EN
2
I
Pull EN above 1.3 V to permit normal ORing operation. A low on EN holds GATE low.
RSVD
3
PWR
This pin must be connected to GND.
GND
4
PWR
Device ground.
GATE
5
O
Connect to the gate of the external MOSFET. Controls the MOSFET to emulate a low forward-voltage diode.
C
6
I
Voltage sense input that connects to the simulated diode cathode, and also serves as the bias supply for the
gate drive charge pump and internal controls. Connect to the MOSFET drain in the typical configuration.
A
7
I
Voltage sense input that connects to the simulated diode anode, and also serves as the reference for the
charge-pump bias supply on BYP. Connect to the MOSFET source in the typical configuration.
BYP
8
I/O
Connect a capacitor from BYP to A to filter the gate drive supply voltage.
5
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DETAILED DESCRIPTION
The following descriptions refer to the pinout and the functional block diagram.
A, C: The A pin serves as the simulated diode anode and the C as the cathode. GATE is driven high when V(A-C)
exceeds 65 mV. A strong GATE pull-down is applied when V(A-C) is less than the programmable turn-off threshold
(see RSET). These two thresholds serve as a hysteretic GATE control with the ON/OFF state preserved until the
next (opposite) threshold cross.
The internal charge pump output, which provides bias power to the comparators and voltage to drive GATE, is
referenced to A. Some charge pump current appears on A.
C is both the cathode voltage sense and the bias supply for the gate-drive charge pump and other internal
circuits. This pin must be connected a source that is 3 V or greater when the external MOSFET is to be turned
on.
A 0.01-μF minimum bypass capacitor to GND is recommended for both A and C inputs. A and C connections to
the bypass capacitor and the controlled MOSFET should be short and low impedance.
The inputs are protected from excess differential voltage by a clamp diode and series resistance. If C falls below
A by more than about 0.7 V, a small current flows out of C. Configurations which permit C to be more than 6 V
lower than A should be avoided.
BYP: BYP is the internal charge pump output, and the positive supply voltage for internal comparator circuits and
GATE driver. A capacitor must be connected from BYP to A. While the capacitor value is not critical, a 2200-pF
ceramic is recommended. Traces to this part must be kept short and low impedance to provide adequate filtering.
Shorting this pin to a voltage below A damages the TPS2419.
EN: A voltage greater than 1.3 V on EN permits the TPS2419 to operate in its normal ORing mode. A voltage
below the lower threshold forces GATE to remain low, however EN going high will not automatically turn GATE
ON. EN going low when GATE is high engages the sustain current pulldown. EN should not be driven higher
than its recommended maximum voltage.
GATE: Gate controls the external N channel MOSFET gate. GATE is driven positive with respect to A by a driver
operating from the voltage on BYP. A time-limited high current discharge source pulls GATE to GND when the
turn-off comparator is activated. The high-current discharge is followed by a sustaining pull-down. The turn-off
circuits are disabled by the thermal shutdown, leaving a resistive pull-down to keep the gate from floating. The
gate connection should be kept low impedance to maximize turn-off current.
GND: This is the input supply reference. GND should have a low impedance connection to the ground plane. It
carries several Amperes of rapid-rising discharge current when the external MOSFET is turned off, and also
carries significant charge pump currents.
RSET: A resistor connected from this pin to GND sets the V(A-C) turn-off comparator threshold. The threshold is
slightly positive when the RSET pin is left open. Current drawn by the resistor programs the turn-off voltage to
increasing negative values. The TPS2419 must have a negative threshold programmed to avoid an unstable
condition at light load. The expression for R(RSET) in terms of the turn-off voltage ( V(OFF)= V(A) - V(C)) follows.
æ
ö
-470.02
÷
R(RSET) = ç
ç V(OFF) - 0.00314 ÷
è
ø
(1)
The units of the numerator are (V × V/A). V(OFF) is positive for V(A) greater than V(C), V(OFF) is less than 3 mV, and
R(RSET) is in ohms.
RSVD: Connect to ground.
6
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TYPICAL CHARACTERISTICS
TURNOFF THRESHOLD
vs
TEMPERATURE
PULSED GATE SINKING CURRENT
vs
GATE VOLTAGE
3.0
5.0
R(RSET) = Open
o
TJ = -40 C
4.5
2.5
4.0
o
TJ = 25 C
I(GATE) − A
V(AC) − mV
2.0
3.5
3.0
2.5
TJ = 85oC
1.5
o
TJ = 125 C
1.0
2.0
0.5
1.5
1.0
−40
0.0
−20
0
20
40
60
80
100
0
120
2
4
6
8
10
V(GATE - GND) − V
o
TJ − Junction Temperature − C
Figure 2.
Figure 3.
TURNON DELAY
vs
V(C)
(POWER APPLIED UNTIL GATE IS ACTIVE)
I(C)
vs
V(C)
(GATE SATURATED HIGH)
60
3.0
50
2.5
o
TJ = -40 C
2.0
o
TJ = 25 C
o
I(VDD) − mA
Delay − ms
40
30
TJ = 125 C
o
TJ = 25 C
1.5
1.0
20
o
TJ = -40 C
o
TJ = 125 C
10
0.5
0
0.0
2
4
6
8
10
12
14
16
18
2
VDD − V
4
6
8
10
12
14
16
18
VC − V
Figure 4.
Figure 5.
7
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TYPICAL CHARACTERISTICS (continued)
TURN ON VOLTAGE
vs
TEMPERATURE
ENABLETHRESHOLD
vs
TEMPERATURE
65.5
1.32
65.4
1.31
65.3
EN - Threshold - V
VON - mV
EN Rising
1.3
65.2
65.1
65
64.9
64.8
1.29
EN Hysteresis ~ 29 mV
1.28
EN Falling
1.27
64.7
1.26
64.6
64.5
-40
-20
0
20
40
60
80
TJ - Temperature - °C
100
1.25
120
-40
-20
Figure 6.
0
20
40
60
80
100
TJ - Junction Temperature - °C
120
Figure 7.
Turn on
Threshold
GATE drives 10 nF to GND
VC = 12 V, RSET = 61.9 WW
VA-C
Turn off
Threshold
10 V/DIV
20 mv/DIV
EXAMPLE TURNON AND TURNOFF
VGATE
Time 1ms/DIV
Figure 8.
8
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TYPICAL CHARACTERISTICS (continued)
EXAMPLE TURNOFF
GATE drives 10 nF to GND
VC = 12 V, RSET = 61.9 WW
1 A/DIV
IGATE
Turn off
Threshold
10 V/DIV
20 mv/DIV
VA-C
VGATE = VA
VGATE
135 ns
Time 100ns/DIV
Figure 9.
9
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APPLICATION INFORMATION
OVERVIEW
The TPS2419 is designed to allow an output ORing in N+1 power supply applications (see Figure 11), and an
input-power bus ORing in redundant source applications (see Figure 12). The TPS2419 and external MOSFET
emulate a discrete diode to perform this unidirectional power combining function. The advantage to this
emulation is lower forward voltage drop and higher efficiency.
The TPS2419 turns the MOSFET on and off like a comparator with hysteresis as shown in Figure 10. GATE is
driven high when V(A-C) exceeds 65 mV, and driven low if V(A-C) falls below the RSET programmed turn-off
threshold. Operation of the TPS2419 is demonstrated in Figure 8 where an ac-coupled square wave is applied
from A to C. Figure 8 shows the condition where the MOSFET gate is initially at GND, and V(A-C) is less than 65
mV. When the turn-on threshold is exceeded, the TPS2419 turns on the MOSFET gate, and charges it to V(BYP).
The gate stays high even though V(A-C) is less than the turn-on threshold. The TPS2419 pulls the gate to GND
when V(A-C) falls below the turn-off threshold.
V(GATE)
System designs should account for the inherent delay between a TPS2419 circuit becoming forward biased, and
the MOSFET actually turning ON. The delay is the result of the MOSFET gate capacitance charge from ground
to its threshold voltage by the 290 μA gate current. If there are no additional sources holding a common ORed
rail voltage up, the MOSFET internal diode will conduct and maintain voltage on the ORed output. The ORed
input supply will experience a momentary large current draw as the MOSFET turns on, shorting the internal diode
and charging the bus capacitance.
Gate
ON
VON
Programmable
Fast Turn-off
Threshold Range
3mV
Gate
OFF
V(AC)
Figure 10. TPS2419 Operation
The operation of the TPS2419 is summarized in Table 2.
Table 2. Operation as a Function of V(AC)
V(A-C) ≤ Turnoff Threshold (1)
TPS2419
(1)
Turnoff Threshold (1) ≤ V(A-C) ≤ 65 mV
Depends on previous state
(Hysteresis region)
Gate pulled to GND
V(A-C) > 65 mV
(1)
GATE pulled high (ON)
Turnoff threshold is established by the value of RSET.
N+1 POWER SUPPLY – TYPICAL CONNECTION
The N+1 power supply configuration shown in Figure 11 is used where multiple power supplies are paralleled for
either higher capacity, redundancy or both. If it takes N supplies to power the load, adding an extra identical unit
in parallel permits the load to continue operation in the event that any one of the N supplies fails. The supplies
are ORed together, rather than directly connected to the bus, to isolate the converter output from the bus when it
is plugged-in or fails short. Thus, the TPS2419 with an external MOSFET emulates the function of the ORing
diode.
ORed supplies are usually designed to share power by various means, although the desired operation could
implement an active and standby concept. Sharing approaches include both passive, or voltage droop, and
active methods. Not all of the output ORing devices may be ON depending on the sharing control method, bus
loading, distribution resistances, and tolerances.
10
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Implementation
Concept
Power
Bus
CBYP
EN
C
RSVD
GATE
GND
BYP
A
DC/DC
Converter
Input
Voltage
Power Conversion Block
Common Bus
DC/DC
Converter
Figure 11. N+1 Power Supply Example
INPUT ORing – TYPICAL CONNECTION
Figure 12 shows how redundant buses may be ORed to a common point to achieve higher reliability. It is
possible to have both MOSFETs ON at once if the bus voltages are matched, or the combination of tolerance
and regulation causes both TPS2419 circuits to see a forward voltage. The ORing MOSFET will disconnect the
lower-voltage bus, protecting the remaining bus from potential overload by a fault.
Backplane
Power Buses
Concept
Implementation
Common
Buses
C
BYP
EN
GATE
A
C
EN
GATE
BYP
A
LOAD
GND
GND
BUS2
BUS1
DC/DC
Converter
CBYP
CBYP
Hotswap
Plug-In Unit
Figure 12. Example ORing of Input Power Buses
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SYSTEM DESIGN AND NOISE ISSUES
In noisy system environments, the low impedance of a MOSFET coupled with a default positive turn off threshold
voltage might result in unwanted ON/OFF GATE cycling. Ideally the best way to approach the problem is with a
clean layout and noise free system design. Since design constraints limit the ability to improve this, the following
suggestions can be employed with the TPS2419.
• Set the turn off threshold negative using the RSET pin. This is required to operate at light load, but does
permit reverse current.
• If current monitoring is used in the system, take advantage of the shunt resistor and connect the A and C pins
across the shunt and FET. This increases the sense resistance, reducing noise sensitivity by increasing the
signal levels while reducing the permitted reverse current.
• Disable the device using EN under light load conditions.
RECOMMENDED OPERATING RANGE
The maximum recommended bus voltage is lower than the absolute maximum voltage ratings on A and C, solely
to provide some margin for transients on the bus. The TPS2419 will operate properly up to the absolute
maximum voltage ratings on A and C.
Most power systems experience transient voltages above or below the normal operating level. Short transients,
or voltage spikes, may be clamped by the ORing MOSFET to an output capacitor and/or voltage rail depending
on the system design. Protection may be required on the input or output if the system design does not inherently
limit transient voltages between the TPS2419 absolute maximum ratings (positive or negative).
Protection for positive transients that would exceed the absolute maximum limits may be accomplished with a
TVS diode (transient voltage suppressor) clamp to ground, or a diode clamp to a safe voltage rail. If a TVS is
required, it must protect to the absolute maximum ratings at the worst case clamping current. Protection for
negative transients that would drive pins (e.g. C) below the absolute maximum limits may be accomplished with a
diode clamp to ground. Limit transient current in or out of the TPS2419 to less than 50 mA. Transients can also
be controlled by bus capacitance or composite snubber/clamps such as a zener-blocked large capacitor with a
discharge resistor in parallel.
MOSFET SELECTION AND R(RSET)
MOSFET selection criteria include voltage rating, voltage drop, power dissipation, size, and cost. The voltage
rating consists of both the ability to withstand the rail voltage with expected transients, and the gate breakdown
voltage. The MOSFET gate rating should exceed be the maximum of the controlled rail voltage or 11.5 V.
While rDS(on) is often chosen with the power dissipation, voltage drop, size and cost in mind, there are several
other factors to be concerned with in ORing applications. When using a TPS2419 with RSET programmed to a
negative voltage, the permitted static reverse current is equal to the turn-off threshold divided by the MOSFET's
rDS(on). While this current may actually be desirable in some systems, the amount may be controlled by selection
of rDS(on) and RSET. The practical range of rDS(on) for a single MOSFET runs from the low milliohms to 40 mΩ for
a single MOSFET.
MOSFETs may be paralleled for lower voltage drop (power loss) at high current. Current sharing depends on the
resistance match including both the rDS(on), connection resistance, and thermal coupling.
The TPS2419 may only be operated without an RSET programming resistor if the loading provides a V(A-C)
greater than 3 mV. A negative turnoff threshold reduces sensitivity to false tripping due to noise on the bus, but
permits larger static reverse current. Installing a resistor from RSET to ground creates a negative shift in the
turn-off threshold per Equation 2.
æ
ö
-470.02
÷
R(RSET) = ç
ç V(OFF) - 0.00314 ÷
è
ø
(2)
12
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Product Folder Link(s): TPS2419
TPS2419
SLVS998B – FEBRUARY 2010 – REVISED SEPTEMBER 2011
www.ti.com
To obtain a -10 mV turnoff ( V(A) is less than V(C) by 10 mV ), R(RSET) = (–470.02/ ( –0.01–0.00314) ) ≈ 35.7 kΩ. If
a 10 mΩ rDS(on) MOSFET was used, the reverse turnoff current would be calculated as follows.
V(THRESHOLD)
I(TURN_OFF) =
r DS(on)
I(TURN_OFF) = -10 mV
10 mW
I(TURN_OFF) = - 1 A
(3)
The sign indicates that the current is reverse, or flows from the MOSFET drain to source ( C to A ).
The turn-off speed of a MOSFET is influenced by the effective gate-source and gate-drain capacitance CISS).
Since these capacitances vary a great deal between different vendor parts and technologies, they should be
considered when selecting a MOSFET where the fastest turn-off is desired.
GATE DRIVE, CHARGE PUMP AND C(BYP)
Gate drive of 290 μA typical is generated by an internal charge pump and current limiter. Make sure to use low
impedance traces and good bypass on A and C to avoid having the large charge pump currents interfere with
voltage sensing. The GATE drive voltage is referenced to V(A) as GATE will only be driven high when V(A) > V(C).
The capacitor on BYP (bypass) must be used in order to form a quiet supply for the internal high-speed
comparator.
Gate Drive Resistance and Output Transients
The strong gate (pulsed) pull-down current can turn the ORing MOSFET(s) off in the 100 - 200 ns time frame.
While this serves to rapidly stop the reverse current buildup, it has a side effect of inducing a voltage transient on
the input bus, the output bus, and ground. One transient source is the GATE turn-off current itself, which excites
parasitic L-C tank circuits. A second transient source is the energy stored in power bus inductance driving a
voltage surge and ringing as reverse MOSFET current is interrupted. Both of these effects can be reduced by
limiting the GATE discharge current with a series resistor in the 10 Ω to 200 Ω range. This both reduces the peak
discharge current, and slows the MOSFET turnoff, reducing the di/dt. A careful tradeoff of peak reverse current
and the effects of the voltage transient may be required.
An example of turnoff speed with and without GATE resistance is illustrated by the circuit of Figure 13. Figure 14
and Figure 15 show GATE, the MOSFET gate, and VC-ac for similar turnoff transients and gate resistors of 0 Ω
and 51 Ω. A substancial reduction in noise is shown for a difference of 90ns in actual current termination. These
techniques may be used in conjunction with clamping and snubbing techniques discussed in RECOMMENDED
OPERATING RANGE. Figure 13 also demonstrates the filtering discussed in the next section.
0.47mF
VIN
VOUT
C
0.47mF
RSET
61.9kW
GATE GND
BYP
A
EN
RGATE2
RGATE1
2200pF
0.47mF
“1”
M1, M2
CSD16401
Figure 13. Circuit for Gate Resistor Waveforms
13
Copyright © 2010–2011, Texas Instruments Incorporated
Product Folder Link(s): TPS2419
TPS2419
Turn on
Threshold
www.ti.com
VC Output
10 V/DIV
100 mv/DIV
AC_Coupled
SLVS998B – FEBRUARY 2010 – REVISED SEPTEMBER 2011
Configuration: 2 x ( CSD16401,
TI with 0W gate resistors)
MOSFET
stops conducting
10 V/DIV
VGATE_MOSFET
VGATE_2419
Time 50ns/DIV
10 V/DIV
10 V/DIV
100 mv/DIV
AC_Coupled
Figure 14. Gate Turnoff Waveforms with RGATE = 0Ω
VC Output
Configuration: 2 x ( CSD16401,
TI with 51W in gate)
MOSFET
stops conducting
VGATE_MOSFET
VGATE_2419
Time 50ns/DIV
Figure 15. Gate Turnoff Waveforms with RGATE = 51Ω
14
Copyright © 2010–2011, Texas Instruments Incorporated
Product Folder Link(s): TPS2419
TPS2419
SLVS998B – FEBRUARY 2010 – REVISED SEPTEMBER 2011
www.ti.com
Input Filtering
Voltage transients, converter switching noise and ripple, and ringing due to current interruptions can potentially
cause undesired on-off cycling, especially at very light loads. This includes voltage gradients (especially at MHz
frequencies) across the ground plane effecting the apparent V(A) and V(C). The effects of these unwanted signals
can be reduced by providing input filtering as shown in Figure 16 and Figure 13. There are two potential
problems that the filter might have to help with, 1) internally generated switching noise, and 2) fast ringing
transients caused by nearby power system events. Case 2 (in Figure 16) filtering is better at suppressing internal
switching noise and Case 1 is better for large bus transients in the megahertz range. The "Z" element in CASE 1
is a high-impedance ferrite bead with low resistance to limit the dc voltage error. The L-C filter limits the apparent
V(A) voltage swings during high-speed transients. The L-C in series with A also causes a phase delay in sensed
steady-state switching noise, creating an apparent additional V(AC).
The filter capacitors should be located close to the TPS2419's GND pin and be connected to GND by a solid
plane. The A-C capacitor should be located directly across the TPS2419 pins. These values were empirically
chosen in a particular test setup and may have to be tuned for different systems.
The waveform of Figure 17 shows turnon in the presence of 135 mVpp ripple by the circuit of Figure 13. The
ORing circuit was loaded with 10 kΩ parallel to 0.1 µF, and had only a -4.5 mV turnoff threshold. This condition is
often difficult to turn on into due to the V(A-C) difference that occurs when the MOSFET diode peak charges the
output. The output voltage was monitored with the oscilloscope probe ac-coupled, causing visual artifacts due to
the probe settling time. The increase in output ripple is evident as the dynamic impedance of the MOSFET diode
is shorted by the channel resistance.
Selection of the A and C sense points can also play a role in limiting unwanted turnoff events. Sensing voltages
at bus bypass capacitors may benefit operation by limiting the apparent switching and transient noise.
The TPS2419 uses C as both a voltage sense and power pin. Placing resistance in this lead will cause a
reduction in V(C) due to IxR voltage drop, changing the apparent turnon and turnoff thresholds.
CASE 2
CASE 1
FROM “GATE”
FROM “GATE”
Z = 600W,
0.1W, 2A
0.47mF
0.47mF
TO “C”
1W
TO “A”
0.47mF
TO “A”
0.47mF
TO “C”
0.47mF
0.47mF
Figure 16. Input Filtering Configurations
15
Copyright © 2010–2011, Texas Instruments Incorporated
Product Folder Link(s): TPS2419
TPS2419
100 mv/DIV
AC_Coupled
SLVS998B – FEBRUARY 2010 – REVISED SEPTEMBER 2011
www.ti.com
135mVPP
200 mV/DIV
VC Output
VA-C
VC = 12 V,
Load = 10 kW || 0.1mF
Note slight (-) offset
in differential probe
15V
VGATE
10V
Time 10ms/DIV
Figure 17. Turnon with Noisy Power Rail
SUMMARIZED DESIGN PROCEDURE
The following is a summarized design procedure:
1. Noise voltage and impedance at the A and C pins should be kept low. A minimum 0.01 μF or more may be
required.
2. Select C(BYP) as 2200 pF, X7R, 25-V or 50-V ceramic capacitor.
3. Select the MOSFET based on considerations of voltage drop, power dissipated, voltage ratings, and gate
capacitance. See sections: MOSFET Selection and RSET.
4. Select R(RSET) based on which MOSFET was chosen and reverse current considerations – see MOSFET
Selection and RSET.
5. Make sure to connect RSVD to ground
Layout Considerations
1. The TPS2419, MOSFET, and associated components should be used over a ground plane.
2. The GND connection should be short and wide, with multiple vias to ground.
3. A and C bypass capacitors should be adjacent to the pins with a minimal ground connection length to the
plane.
4. The GATE connection should be short and wide (e.g., 0.025" minimum).
5. Route the A and C sense lines away from noisy sources, and avoid large ground bounce between the
MOSFET and TPS2419.
6. R(SET) should be kept immediately adjacent to the TPS2419 with short leads.
7. C(BYP) should be kept immediately adjacent to the TPS2419 with short leads.
16
Copyright © 2010–2011, Texas Instruments Incorporated
Product Folder Link(s): TPS2419
TPS2419
SLVS998B – FEBRUARY 2010 – REVISED SEPTEMBER 2011
www.ti.com
REVISION HISTORY
Changes from Original (February 2010) to Revision A
Page
•
Changed the data sheet From: Preview To: Production Data .............................................................................................. 1
•
Changed the Overview section - paragraph 2 From: MOSFET gate is initially low, and V(AC) is less than 64 mV. To:
MOSFET gate is initially at GND, and V(A-C) is less than 65 mV. ........................................................................................ 10
•
Changed the Overview section - paragraph 2, From: The TPS2419 turns on the MOSFET gate, and charges it to
V(BYP) once the turn-on threshold is exceeded. To: When the turn-on threshold is exceeded, the TPS2419 turns on
the MOSFET gate, and charges it to V(BYP) ........................................................................................................................ 10
•
Changed the Overview section - paragraph 3 From: The ORed input supply will experience a momentary large load
as the MOSFET turns on, shorting the internal diode and charging the bus capacitance. To: The ORed input supply
will experience a momentary large current draw as the MOSFET turns on, shorting the internal diode and charging
the bus capacitance. ........................................................................................................................................................... 10
•
Changed the RECOMMENDED OPERATING RANGE section, paragraph 1 From: The TPS2419 will operate
properly up to the absolute maximum voltage ratings on A, C, and VDD. To: The TPS2419 will operate properly up to
the absolute maximum voltage ratings on A and C. ........................................................................................................... 12
Changes from Revision A (March 2010) to Revision B
•
Page
Added updated marking information ..................................................................................................................................... 2
17
Copyright © 2010–2011, Texas Instruments Incorporated
Product Folder Link(s): TPS2419
PACKAGE OPTION ADDENDUM
www.ti.com
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)
TPS2419D
ACTIVE
SOIC
D
8
75
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
2419D
TPS2419DR
ACTIVE
SOIC
D
8
2500
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
2419D
TPS2419PW
ACTIVE
TSSOP
PW
8
150
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
2419
TPS2419PWR
ACTIVE
TSSOP
PW
8
2000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
2419
(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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