TI LFC789D25CDR Dual linear fet controller Datasheet

SLLS565B − MARCH 2003 − REVISED SEPTEMBER 2004
D Two Independent Controllers for
D OR PW PACKAGE
(TOP VIEW)
Regulation of:
− Fixed 2.5-V and an Adjustable Output
− ±2% (Max) Regulation Across
Temperature and Load (1 mA to 3 A)
DRV_VADJ
SEN_VADJ
VREF
GND
D Adjustable Output Can Be Set Via an
External Reference Pin, Allowing for the
Creation of a Tracking Regulator
1
8
2
7
3
6
4
5
VCC
DRV_V25
SEN_V25
NC
NC − No internal connection
D Great Design Flexibility With Minimal
External Components
D Applications: High-Current, Low-Dropout
Regulators for:
− DDR/RDRAM Memory Termination
− Motherboards
− Chipset I/O
− GTLP Termination
description/ordering information
The LFC789D25 is a dual linear FET controller that simplifies the design of dual power supplies. The device
consists of two independent controllers, each of which drives an external MOSFET to implement a low-dropout
regulator. One controller is programmed to regulate a fixed 2.5-V output, while the second controller can be
programmed to regulate any desired output voltage via a reference input pin, allowing for the creation of a
tracking regulator often needed for termination schemes. And, because heating effects of the external FETs
easily can be isolated from the controllers, the controllers can regulate the output voltages to a maximum
tolerance of ±2% across temperature and load.
The LFC789D25 allows designers a great deal of flexibility in selecting external components and topology to
implement their specific power-supply needs. With appropriate heat sinking, the designer can build a regulator
with as much current capability as allowed by the external MOSFET and power supply. And, because the
dropout of the regulator simply is the product of the RDS(on) of the external power MOSFET and the load current,
very low dropout can be achieved via proper selection of the power MOSFET.
Packaged in 8-pin SOIC and space-saving TSSOP, the LFC789D25 is characterized for operation from 0°C to
70°C.
ORDERING INFORMATION
ORDERABLE
PART NUMBER
PACKAGE†
TA
SOIC (D)
0°C to 70°C
TSSOP (PW)
Tube of 75
LFC789D25CD
Reel of 2500
LFC789D25CDR
Tube of 150
LFC789D25CPW
Reel of 2000
LFC789D25CPWR
TOP-SIDE
MARKING
KADAC
KADAC
† Package drawings, standard packing quantities, thermal data, symbolization, and PCB design guidelines
are available at www.ti.com/sc/package.
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.
Copyright  2004, Texas Instruments Incorporated
!" #$
# % & ## '($ # ) # "( "#
) "" $
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1
SLLS565B − MARCH 2003 − REVISED SEPTEMBER 2004
functional block diagram
DRV_VADJ
SEN_VADJ
VREF
+
_
1
8
VCC
2
3
Bandgap
Reference
+
_
7
6
DRV_V25
SEN_V25
4 kΩ
3.6 kΩ
GND
4
5
NC
PIN DESCRIPTION
PIN
PIN NAME
PIN FUNCTION
1
DRV_VADJ
SEN_VADJ
Output of adjustable controller. Drives gate(s) of FET(s) to output user-programmable voltage (VADJ).
Input pin used to program VADJ, allowing VADJ to track changes in VREF
4
VREF
GND
5
NC
No connection
6
Sense Input of 2.5-V controller. Senses changes in 2.5-V supply.
7
SEN_V25
DRV_V25
8
VCC
Power supply for device
2
3
2
Sense input of adjustable controller. Senses changes in VADJ.
Ground
Output of 2.5-V controller. Drives gate(s) of FET(s) to output fixed 2.5 V.
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SLLS565B − MARCH 2003 − REVISED SEPTEMBER 2004
VCC (12V)
VPWR (3.3V)
LFC789D25
1
DRV_VADJ
VREF
1.25 V
C4
0.1 µF
DRV_V25
C3
22 µF
7
VDDQ
2.5 V
2
3
C5
0.1 µF
VCC
8
4
C1
100 µF
SEN_VADJ
SEN_V25
VREF
C2
100 µF
6
GND
R1†
R2†
† R1 = R2 = 100 Ω (0.1% matched resistors)
Figure 1. Typical Application Circuit for DDR1 − Memory Voltage (VDDQ) and VREF Buffer for DIMMs
absolute maximum ratings over operating free-air temperature range (unless otherwise noted)‡
Supply voltage, VCC (see Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 V
Input voltage range, VREF, SEN_VADJ, SEN_V25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3 V to 18 V
Package thermal impedance, θJA (see Notes 2 and 3): D package . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97°C/W
PW package . . . . . . . . . . . . . . . . . . . . . . . . . 149°C/W
Operating virtual junction temperature, TJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150°C
Storage temperature range, Tstg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −65°C to 150°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.
NOTES: 1. All voltage values are with respect to the network ground terminal.
2. Maximum power dissipation is a function of TJ(max), θJA, and TA. The maximum allowable power dissipation at any allowable
ambient temperature is PD = (TJ(max) − TA)/θJA. Operating at the absolute maximum TJ of 150°C can impact reliability.
3. The package thermal impedance is calculated in accordance with JESD 51-7.
recommended operating conditions
VCC
TA
MIN
MAX
Supply voltage
9
16
V
Operating free-air temperature
0
70
°C
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UNIT
3
SLLS565B − MARCH 2003 − REVISED SEPTEMBER 2004
electrical characteristics, VCC = 12 V ± 5%, TA = 25°C (unless otherwise noted)
PARAMETER
I SEN_V
TA
TEST CONDITIONS
MIN
VDRV
VADJ sense-pin current
25
V25 sense-pin current
Full range
−500
125
Driver output voltage
V25 = 2.5 V
IDRV
Driver output current
IV
Pin current, VREF
Output regulation
(see Figure 1)
4
500
IDRV = 0
VDRV = 4 V,
VSEN = 0.8 VOUT (nom)
Full range
VCC − 3
ICC
UNIT
Full range
5
VADJ output voltage
regulation
IOUT = 1 mA to 2 A,
VPWR = 3.3 V ±10%,
VREF = V25/2
mA
−250
−500
Full range
2.45
2.5
2.55
V
VREF
Full range
Full range
POST OFFICE BOX 655303
nA
2.5
0.98 ×
VREF
VREF
1.02 ×
VREF
2
Supply current
µA
A
10
Full range
IOUT = 1 mA to 3 A,
VPWR = 3 .3 V ± 10%
nA
V
−20
REF
V25 output voltage
regulation
Supply
Full range
VCC
− 1.5
Driver
Reference
MAX
−20
ADJ
Sense
I SEN_V
TYP
• DALLAS, TEXAS 75265
2.5
mA
SLLS565B − MARCH 2003 − REVISED SEPTEMBER 2004
APPLICATION INFORMATION
FUNCTIONAL DESCRIPTION
A linear voltage regulator can be broken down into four essential building blocks: a pass transistor, a voltage
reference, a feedback network, and a control circuit to drive the pass element, based on the comparison
between the output voltage (as sampled by the feedback network) and the voltage reference. With the exception
of the pass transistor, the -ADJ provides the other three building blocks needed. Thus, with minimal external
components and low overall solution cost, a designer can create two independent, tightly regulated output
voltages capable of delivering high currents in excess of 3 A (as limited by the external pass transistor). One
output is fixed at 2.5 V. The other output can be adjusted to any desired voltage via an externally applied signal
to the VREF pin. Because the output of the regulator always tracks any changes to this VREF pin, it is relatively
easy to implement a tracking regulator. See the typical application circuit (Figure 1).
internal reference
The fixed 2.5-V output controller uses an internal temperature-compensated bandgap reference centered at
1.2 V. Its tolerance is designed to be <±2% over the specified temperature range, which, when coupled with the
low offset of the driver circuit, allows the 2.5-V output to have a tolerance of 2% over the specified temperature
range and full load.
external reference pin (VREF)
For the adjustable output controller, the VREF pin allows great flexibility for the designer. Taking a simple resistor
divider tied to an external voltage source and connecting the divider to the VREF pin allows the controller to
regulate an output voltage that is some fraction of the external voltage source. And, because any changes in
the external voltage source are sensed by the voltage divider, the regulated output tracks those changes.
If a tracking regulator is not desired, a fixed voltage can be achieved by applying a constant voltage to the VREF
pin. This signal can be provided by a simple device such as the TL431 adjustable shunt regulator.
The VREF pin typically sources a current of 20 nA and, as such, has a minimal loading effect on the resistor
divider or the shunt regulator. The accuracy of the adjustable output depends on the accuracy of the signal
applied to the VREF pin. Using high-precision resistors or a TL431A (1% output tolerance) helps achieve good
accuracy.
feedback network (SENSE pins)
The 2.5-V controller senses the output voltage via the SEN_V25 pin. This pin is tied to an internal resistor divider
that essentially halves the sensed output voltage and feeds it back to the controller for comparison to the internal
bandgap reference.
For the adjustable output controller, the SEN_VADJ pin provides direct feedback of the output voltage to the
controller for comparison to the externally applied VREF signal.
controller/driver
Both drivers essentially are error amplifiers that can output a worst-case minimum of 9 V (10.5 V at 25°C) when
the LFC789D25 is powered by 12 V. This allows the controllers to regulate a large range of output
voltages, as limited by the threshold voltages of the external NMOS. Both drivers sample the output voltage via
a SEN pin. For the adjustable version, this SEN pin typically sources a current of 20 nA and, thus, has minimal
loading on the output voltage. For the 2.5-V version, this SEN pin sinks a current of approximately 125 µA
(including the currents through the internal resistor divider); this results in minimal loading on the output voltage.
Although not tested, both of these controllers are designed with very low offset (typically less than 4 mV),
resulting in very accurate control of the drive signals.
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APPLICATION INFORMATION
MOSFET SELECTION: BENEFITS OF NMOS PASS ELEMENTS REVISITED
A great benefit of having an external pass element is that the control circuitry can be powered by a separate
supply (VCC), other than the one used as the input to the pass element (VPWR). This feature allows the use of
an NMOS pass element, which requires a positive VGS > VT for operation. With a separate VCC pin to the
controller, the voltage at the gate of the NMOS readily can exceed the voltage at the drain; thus, VGS easily can
exceed VDS + VT, allowing the NMOS to operate in the triode region (VDS ≥ VGS − VT). In the triode region, VDS
can be very small, thus achieving very low dropout.
D
The external NMOS selected for the pass transistor has significant impact on the overall characteristics of the
regulator, as discussed in the following paragraphs.
Maximum output current
D
A benefit of an external pass element is that the designer can size the NMOS to easily sustain the maximum
IOUT expected. This allows great flexibility, along with cost and space savings, because each regulator has its
pass element tailored to its individual needs. In addition, using an NMOS pass element allows for smaller size
(and subsequently, lower cost) than a PMOS element for the same current-carrying ability.
Dropout
D
Choosing an NMOS with very low RDS(on) characteristics provides the regulator with very low dropout because
dropout will be ∼IOUT × RDS(on). This lower dropout also results in better efficiency and lower heat dissipation
in the pass element for a given IOUT.
Maximum programmable output voltage and NMOS threshold voltage, VT
The maximum output voltage that can be regulated by the programmable regulator depends on the device’s
power supply (VCC) and threshold voltage (VT) of the NMOS. With the drive voltage tied to the gate and VOUT
connected to the source of the NMOS, a minimum VGS = VT must be maintained in order to maintain the
n-channel inversion layer. The maximum VOUT is calculated as follows:
VOUT = VS = VG − VT
D
With VCC = 12 V and a corresponding worst-case gate drive voltage of 9 V, the highest achievable
VOUT = 9 V − VT.
Stability
A quality of the old npn regulators was their inherent stability under almost any type of load conditions and output
capacitors. An NMOS regulator has the same benefit. Thus, capacitor selection and
equivalent-series-resistance (ESR) values are not needed for stability, but still should be chosen properly for
best transient response (see below).
capacitor selection
Cout: Although a minimum capacitance is not needed for stability with an NMOS pass device, higher capacitance
values improve transient response. In addition, low-ESR capacitors also help transient response. Tantalum or
aluminum electrolytics can be used for bulk capacitances, while ceramic bypass capacitors can be used to
decouple high-frequency transients due to their low ESL (equivalent series inductance).
Cin: Input capacitors placed at the drain of the NMOS pass transistor (VPWR) help improve the overall transient
response by suppressing surges in VPWR during fast load changes. Low-ESR tantalum or aluminum electrolytic
capacitors can be used; higher capacitance values improve transient response. A 0.1-µF ceramic capacitor can
be placed at the VCC pin of the LFC789D25 to provide bypassing.
6
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APPLICATION INFORMATION
layout
Another benefit of a separate controller and pass element is that the heat dissipated in the external NMOS can
be well isolated from the controller, which has very low power dissipation. Both of these factors allow the
bandgap reference and control circuitry to operate over a more stable temperature range, resulting in very good
accuracy over full-load conditions. The LFC789D25 should be placed as close as possible to the external pass
element because short PCB traces allow minimal EMI coupling to both the drive and sense lines.
For best accuracy, connect the SEN pins as close to the load as possible, not to the source of the NMOS. Also,
place the SEN trace in the same direction and plane as the power trace that connects the source of the NMOS
to the load. Also, it is good practice to keep the load current return path as far as possible from the SEN trace.
Place the 0.1-µF bypass capacitor as close as possible to the VCC pin and connect it directly to the ground plane.
The GND pin of the LFC789D25 should be connected to the ground plane.
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PACKAGE OPTION ADDENDUM
www.ti.com
4-Mar-2005
PACKAGING INFORMATION
Orderable Device
Status (1)
Package
Type
Package
Drawing
Pins Package Eco Plan (2)
Qty
Lead/Ball Finish
MSL Peak Temp (3)
LFC789D25CD
ACTIVE
SOIC
D
8
75
Pb-Free
(RoHS)
CU NIPDAU
Level-2-260C-1 YEAR/
Level-1-235C-UNLIM
LFC789D25CDR
ACTIVE
SOIC
D
8
2500
Pb-Free
(RoHS)
CU NIPDAU
Level-2-260C-1 YEAR/
Level-1-235C-UNLIM
LFC789D25CPW
ACTIVE
TSSOP
PW
8
150
Pb-Free
(RoHS)
CU NIPDAU
Level-1-250C-UNLIM
LFC789D25CPWR
ACTIVE
TSSOP
PW
8
2000
Pb-Free
(RoHS)
CU NIPDAU
Level-1-250C-UNLIM
(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)
Eco Plan - May not be currently available - please check http://www.ti.com/productcontent for the latest availability information and additional
product content details.
None: Not yet available Lead (Pb-Free).
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements
for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered
at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Green (RoHS & no Sb/Br): TI defines "Green" to mean "Pb-Free" and in addition, uses package materials that do not contain halogens,
including bromine (Br) or antimony (Sb) above 0.1% of total product weight.
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDECindustry standard classifications, and peak solder
temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is
provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the
accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take
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In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI
to Customer on an annual basis.
Addendum-Page 1
MECHANICAL DATA
MTSS001C – JANUARY 1995 – REVISED FEBRUARY 1999
PW (R-PDSO-G**)
PLASTIC SMALL-OUTLINE PACKAGE
14 PINS SHOWN
0,30
0,19
0,65
14
0,10 M
8
0,15 NOM
4,50
4,30
6,60
6,20
Gage Plane
0,25
1
7
0°– 8°
A
0,75
0,50
Seating Plane
0,15
0,05
1,20 MAX
PINS **
0,10
8
14
16
20
24
28
A MAX
3,10
5,10
5,10
6,60
7,90
9,80
A MIN
2,90
4,90
4,90
6,40
7,70
9,60
DIM
4040064/F 01/97
NOTES: A.
B.
C.
D.
All linear dimensions are in millimeters.
This drawing is subject to change without notice.
Body dimensions do not include mold flash or protrusion not to exceed 0,15.
Falls within JEDEC MO-153
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