SC1548
Linear FET Controller
POWER MANAGEMENT
Description
Features
The SC1548 is a power supply controller designed to
provide a simple single regulated power supply with over
current protection. It is part of Semtech’s SmartLDO™
family of products. The SC1548 can provide a 1.818V
power supply for the I/O plane or 1.515V for GTL+ / AGP
from either 3.3V or 2.5V. An adjustable option allows
generation and control of any voltage from 1.263V up to
5V.
± 2.5% output accuracy over line, load and
temperature
1.515V, 1.818V and adjustable output voltage
options available
Enable control
Over current protection
5-pin SOT-23 package
Applications
SC1548 features include tight output voltage regulation,
an enable control and over current protection. Over
current protection is provided by feedback to the sense
pin. If the output drops below 50% of the nominal
output voltage (typical) for greater than 4ms (typical), the
output will be shut down.
Motherboards
Graphics cards
Microcontrollers
Simple power supplies
The SC1548 is available in a tiny 5-pin SOT-23 surface
mount package.
Typical Application Circuit
Fixed Output Voltage Versions
3.3V IN
Q1
IRL530N
1.818V OUT
+
C1
100uF
+
C2
100uF
+
C3
22uF
12V IN
U1
1
2
3
SNS
EN
5
ENABLE
GND
DRV
IN
4
SC1548CSK-1.8
C4
0.1uF
Adjustable Output Voltage Version
3.3V IN
Q1
IRL530N
2.5V OUT
R1
97.6
+
C1
100uF
+
C2
100uF
+
12V IN
C3
22uF
U1
1
2
R2
100
3
ADJ
EN
1
ENABLE
GND
DRV
IN
SC1548CSK
Revision: November 10, 2004
5
4
C4
0.1uF
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SC1548
POWER MANAGEMENT
Absolute Maximum Ratings
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified
in the Electrical Characteristics section is not implied. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device
reliability.
Parameter
Symbol
Maximum
Units
VIN
-0.5 to +15
V
VADJ, VEN, VSNS
-0.5 to +7
V
Thermal Impedance Junction to Case
θJ C
81
°C/W
Thermal Impedance Junction to Ambient
θJ A
256
°C/W
Operating Ambient Temperature Range
TA
0 to +70
°C
Operating Junction Temperature Range
TJ
0 to +125
°C
Storage Temperature Range
TSTG
-65 to +150
°C
Lead Temperature (Soldering) 10 Sec
TLEAD
300
°C
Input Supply Voltage
Input Pins
Electrical Characteristics(1)
Unless specified: TA = 25°C, VIN = 12V, VPWR = 3.3V, IOUT = 0A. Values in bold apply over full operating temperature range.
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
11.28
12.00
12.72
V
1.0
1.5
mA
IN
Supply Voltage
VIN
Quiescent Current
IQ
2.0
Undervoltage Lockout
Start Threshold
UVLO
7
8
9
V
100
150
µA
2.3
V
EN
Enable Pin Current
IEN
V E N = 0V
Threshold Voltage
VTH(EN)
VEN rising
Hysteresis
VHYST
Enable Delay Time(2)(3)
tD(ON)
Disable Delay Time(2)(3)
tD(OFF)
1.8
200
mV
VEN = Low to High, measured from
VEN = VTH(EN) to 10% VDRV
500
ns
VEN = High to Low, measured from
VEN = VTH(EN) to 90% VDRV
150
ns
SNS (Fixed Output Voltage Parts)
Sense Pin Current
ISNS
Sinking
75
100
125
µA
ADJ (Adjustable Output Voltage Parts)
Adjust Pin Current
IADJ
Sourcing
Reference Voltage(2)
V AD J
3.0V ≤ VPWR(4) ≤ 3.6V, 1mA ≤ IOUT ≤ 1A
0.25
-1.5%
-2.5%
2004 Semtech Corp.
2
1.263
µA
+1.5%
V
+2.5%
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SC1548
POWER MANAGEMENT
Electrical Characteristics (Cont.)(1)
Unless specified: TA = 25°C, VIN = 12V, VPWR = 3.3V, IOUT = 0A. Values in bold apply over full operating temperature range.
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
-1.5%
VOUT
+1.5%
V
Output Voltage Regulation (Fixed Output Voltage Parts)
Output Voltage(2)
VOUT
3.0V ≤ VPWR(4) ≤ 3.6V, 1mA ≤ IOUT ≤ 1A
-2.5%
+2.5%
DRV
Output Current
IDRV
VDRV = 4V, VSNS = 1.2V
5
10
mA
Output Voltage
VDRV
Full On, IDRV = 0mA
9.0
10.5
V
Rise Time(2)(3)
tr
VEN = Low to High, measured from
VEN = VTH(EN) to 90% VDRV
1.0
ms
Fall Time(2)(3)
tf
VEN = High to Low, measured from
VEN = VTH(EN) to 10% VDRV
550
µs
Overcurrent Protection
Trip Threshold
VTH(OC)
Power-up Output Short
Circuit Immunity
Output Short Circuit Glitch
Immunity
30
50
70
%VOUT
1
5
60
ms
0.5
4
30
ms
Control Section
Bandwidth
VDRV = 9V, THD = 5%, CL = 600pF
5
MHz
Notes:
(1) This device is ESD sensitive. Use of standard ESD handling precautions is required.
(2) See Application Circuit on page 1.
(3) See Timing Diagram on page 4.
(4) Connected to FET drain.
2004 Semtech Corp.
3
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SC1548
POWER MANAGEMENT
Timing Diagram
2004 Semtech Corp.
4
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SC1548
POWER MANAGEMENT
Pin Configuration
Ordering Information
Part Number(1)(2)
Top View
SC1548CSK-X.XTR
SC1548CSKTRT(3)
P ackag e
SOT-23-5
Notes:
(1) Where -X.X denotes voltage options. Available
voltages are: 1.515V (-1.5) and 1.818V (-1.8). Leave blank
for adjustable version.
(2) Only available in tape and reel packaging. A reel
contains 3000 units.
(3) Lead free product. This product is fully WEEE and
RoHS compliant.
SOT-23-5L
Block Diagram
Pin Descriptions
Pin
1
Pin Name Pin Function
SNS
Regulator sense input for fixed output voltage options. Use as a remote sense to the source of the
N-channel MOSFET.
AD J
Regulator sense i nput for adjustable output voltage versi on. Set output voltage as follows (refer to
application circuit on page 1):
R1
VO = 1 .263 • 1 +
R2
2
GND
Ground.
3
DRV
O u t p u t o f r e g u l a t o r. D r i v e s t h e g a t e o f a n N - c h a n n e l M O S F E T t o m a i n t a i n t h e o u t p u t
voltage desired.
4
IN
+12V supply.
5
EN
A c t i ve hi g h e na b l e c o nt r o l w i t h i nt e r na l p ul l up . O ut p ut o f r e g ul a t o r t ur ns o f f w he n E N i s
taken low.
2004 Semtech Corp.
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SC1548
POWER MANAGEMENT
Typical Characteristics(1)
1000
Quiescent Current vs.
Start Threshold vs.
Junction Temperature
Junction Temperature
9.0
VIN = 12V, VEN = 3.3V
900
8.5
800
8.0
600
UVLO (V)
IQ (µA)
700
500
400
7.5
7.0
300
200
6.5
100
0
6.0
0
25
50
75
100
0
125
25
50
2.30
Enable Hysteresis vs.
vs. Junction Temperature
Junction Temperature
500
2.20
400
2.15
350
2.10
300
2.05
2.00
125
100
125
100
125
250
200
1.95
150
1.90
100
1.85
50
1.80
0
0
25
50
75
100
125
0
25
50
150
Enable Pin Current vs.
Enable Delay Time vs.
Junction Temperature
Junction Temperature
1000
VIN = 12V
VEN = 0V
125
75
TJ (°C)
TJ (°C)
VIN = 12V
900
800
700
tD(ON) (ns)
100
IEN (µA)
100
VIN = 12V
VEN falling
450
VHYST (mV)
VTH(EN) (V)
Enable Threshold Voltage
VIN = 12V
VEN rising
2.25
75
TJ (°C)
TJ (°C)
75
50
600
500
400
300
200
25
100
0
0
0
25
50
75
100
125
0
TJ (°C)
2004 Semtech Corp.
25
50
75
TJ (°C)
6
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SC1548
POWER MANAGEMENT
Typical Characteristics (Cont.)(1)
200
Disable Delay Time vs.
Sense Pin Current vs.
Junction Temperature
Junction Temperature
125
VIN = 12V
115
150
110
125
ISNS (µA)
tD(OFF) (ns)
VIN = 12V
VEN = 3.3V
VSNS = VO(NOM)
120
175
100
75
105
100
95
90
50
85
25
80
0
75
0
25
50
75
100
125
0
25
50
TJ (°C)
12.00
Output Voltage (SC1548CSK-1.8)
Junction Temperature
vs. Junction Temperature
1.845
125
VIN = 12V
VEN = 3.3V
3.0V ≤ VPWR ≤ 3.6V
1mA ≤ IO ≤ 1A
1.840
1.835
1.830
11.00
1.825
VO (V)
VDRV (V)
100
Drive Output Voltage vs.
VIN = 12V
VSNS = 0V
IDRV = 0mA
11.50
75
TJ (°C)
10.50
1.820
1.815
1.810
10.00
1.805
1.800
9.50
1.795
9.00
1.790
0
25
50
75
100
0
125
25
50
1.2
Power-Up Output Short Circuit Immunity
vs. Junction Temperature
vs. Junction Temperature
10
Power-up Short Circuit Immunity (ms)
0.8
VTH(OC) (V)
100
OCP Trip Threshold (SC1548CSK-1.8)
VIN = 12V
VEN = 3.3V
1
75
125
TJ (°C)
TJ (°C)
0.6
0.4
0.2
0
VIN = 12V
VEN switched from 0V to 3.3V
ROUT = 0Ω
Two representative parts
shown
9
8
7
6
5
4
3
2
1
0
0
25
50
75
100
125
0
TJ (°C)
2004 Semtech Corp.
25
50
75
100
125
TJ (°C)
7
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SC1548
POWER MANAGEMENT
Typical Characteristics (Cont.)(1)
Output Short Circuit Glitch Immunity
Drive Pin Rise Time vs.
vs. Junction Temperature
Junction Temperature
1200
VIN = 12V
VEN = 3.3V
ROUT of 0Ω applied to output
Two representative parts shown
7
6
1000
800
tr (µs)
5
4
3
600
400
2
VIN = 12V
VEN switched from 0V to 3.3V
Two representative parts shown
200
1
0
0
0
25
50
75
100
0
125
25
SC1548CSK-1.8 Small Signal Gain
Junction Temperature
and Phase Shift vs. Frequency
80
VIN = 12V
VEN switched from 3.3V to 0V
Two representative parts shown
900
800
100
Drive Pin Fall Time vs.
1000
IOUT = 1.8A
60
125
0
-45
40
700
-90
f (Hz)
500
400
300
200
20
-135
0
-180
-20
-225
-40
-270
-60
100
0
0
25
50
75
100
-80
1.00E+02
125
Phase
1.00E+03
TJ (°C)
-360
1.00E+06
1.00E+05
SC1548CSK-1.5 Small Signal Gain
SC1548CSK Small Signal Gain
and Phase Shift vs. Frequency
and Phase Shift vs. Frequency
80
0
IOUT = 1.8A
40
-90
Gain
20
-135
0
-180
-20
-225
-40
-270
-60
Phase
2004 Semtech Corp.
1.00E+04
f (Hz)
1.00E+05
VOUT = 2V
IOUT = 1.8A
60
40
0
-45
-90
Gain
Gain (dB)
-45
Phase (°)
60
1.00E+03
-315
Gain (dB)
80
-80
1.00E+02
1.00E+04
Phase (°)
Gain
600
tf (µs)
75
TJ (°C)
TJ (°C)
Gain (dB)
50
20
-135
0
-180
-20
-225
Phase (°)
Short Circuit Glitch Immunity (ms)
8
Phase
-315
-40
-270
-60
-315
-80
1.00E+02
-360
1.00E+06
1.00E+03
1.00E+04
1.00E+05
-360
1.00E+06
f (Hz)
8
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SC1548
POWER MANAGEMENT
Typical Characteristics (Cont.)(1)
Load Transient Response, Expanded
Load Transient Response
Trace 1: VOUT, AC coupled, 50mV/div.
Trace 2: VDRV, 2V/div.
Trace M3: load stepping from 0A to 1A
Timebase: 1µs/div
Trace 1: VOUT, AC coupled, 50mV/div.
Trace 2: VDRV, 2V/div.
Trace M3: load stepping from 0A to 1A to 0A
Timebase: 10µs/div
Load Transient Response, Expanded
Disable Delay Time, tD(OFF)
Trace 1: VDRV, 1V/div.
Trace 2: VEN, 2V/div.
Timebase: 100ns/div
tD(OFF) ≈ 36ns
Trace 1: VOUT, AC coupled, 50mV/div.
Trace 2: VDRV, 2V/div.
Trace M3: load stepping from 1A to 0A
Timebase: 1µs/div
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SC1548
POWER MANAGEMENT
Typical Characteristics (Cont.)(1)
Enable Delay Time, tD(ON)
Drive Output Fall Time, tf
Trace 1: VDRV, 1V/div.
Trace 2: VEN, 2V/div.
Timebase: 100ns/div
tf ≈ 350ns
Trace 1: VDRV, 1V/div.
Trace 2: VEN, 2V/div.
Timebase: 250ns/div
tD(ON) ≈ 550ns
Drive Output Rise Time, tr
Power-up Output Short Circuit Immunity
Trace 1: VDRV, 1V/div.
Trace 2: VEN, 2V/div.
Timebase: 500µs/div
tr ≈ 1ms
2004 Semtech Corp.
Trace 1: VDRV, 5V/div.
Trace 2: VEN, 2V/div.
Timebase: 2ms/div
SC1548 enabled into a short, therefore VOUT < VTH(OC)
immediately the device is enabled. This device shuts
down after 8ms.
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SC1548
POWER MANAGEMENT
Typical Characteristics (Cont.)(1)
Note:
(1) See Applications Circuit on page 1.
Output Short Circuit Glitch Immunity
Trace 1: VDRV, 5V/div.
Trace 2: VOUT, 1V/div.
Timebase: 1ms/div
SC1548 enabled, then shorted, therefore
VOUT < VTH(OC) immediately the short is applied. This
device shuts down after 5ms.
Applications Infomation
Theory Of Operation
The SC1548 linear FET controller provides a simple way
to drive an N-channel MOSFET to produce a tightly
regulated output voltage from an available, higher,
supply voltage. It takes its power from a 12V supply,
drawing typically 2mA while operating.
Also included is an overcurrent protection circuit that
monitors the output voltage. If the output voltage drops
below 50% of nominal, as would occur during an
overcurrent or short condition, the device will pull the
drive pin low and latch off.
It contains an internal bandgap reference which is
compared to the output voltage via a resistor divider.
This resistor divider is internal on the fixed output
voltage options, and user selectable on the adjustable
option. Since the drive pin can pull up to a 9V
guaranteed minimum, the device can be used to
regulate a large range of output voltages by careful
selection of the external MOSFET (see component
selection, below).
Fixed Output Voltage Options
Please refer to the Application Circuit on Page 1. The
fixed output voltage parts have an internal resistor
divider that draws a nominal 100µA from the output.
The voltage at the common node of the resistor divider
is then compared to the bandgap reference voltage of
1.263V. The drive pin voltage is then adjusted to
maintain the output voltage set by the resistor divider.
Referring to the block diagram on page 5, the nominal
resistor values are:
The SC1548 includes an active high enable control with
an internal pullup resistor. If this pin is pulled low, the
drive pin is pulled low, turning off the N-channel MOSFET.
If the pin is left open or pulled up to 2.5V, 3.3V or 5V,
then the drive pin will be enabled.
2004 Semtech Corp.
11
Output Voltage
R1 (kΩ)
R2 (kΩ)
1.515V
2.52
12.63
1.818V
5.55
12.63
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SC1548
POWER MANAGEMENT
Applications Infomation (Cont.)
It is possible to adjust the output voltage of the fixed
voltage options, by applying an external resistor divider
to the sense pin (please refer to Figure 1 below). Since
the sense pin sinks a nominal 100µA, the resistor
values should be selected to allow 10mA to flow through
the divider. This will ensure that variations in this current
do not adversely affect output voltage regulation. Thus a
target value for R2 (maximum) can be calculated:
R2 ≤
V OUT ( FIXED )
Ω
10 mA
The output voltage can only be adjusted upwards from the fixed
output voltage, and can be calculated using the
following equation:
VOUT ( ADJUSTED
)
R1
= VOUT ( FIXED ) • 1 +
+ R1 • 100 µ A
R2
12V IN
VPWR
Q1
Volts
VOUT
R1
+
C1
100uF
+
C2
100uF
+
C3
22uF
U1
1
2
R2
3
SNS EN
5
ENABLE
GND
DRV
IN
4
C4
0.1uF
SC1548CSK-X.X
Figure 1: Adjusting The Output Voltage of Fixed Output Voltage Options
12V IN
VPWR
Q1
VOUT
R1
+
C1
100uF
+
C2
100uF
+
C3
22uF
U1
1
2
R2
3
ADJ
EN
5
ENABLE
GND
DRV
IN
4
SC1548CSK
C4
0.1uF
Figure 2: Setting The Output Voltage of the Adjustable Output Voltage Option
Adjustable Output Voltage Option
Again, a target value for R2 (maximum) can be
calculated:
The adjustable output voltage option does not have an
internal resistor divider. The adjust pin connects directly
to the inverting input of the error amplifier, and the
output voltage is set using external resistors (please
refer to Figure 2 above). In this case, the adjust pin
sources a nominal 0.5µA, so the resistor values should
be selected to allow 50µA to flow through the divider.
2004 Semtech Corp.
R2 ≤
1 . 263 V
50 µ A
Ω
The output voltage can be calculated as follows:
R1
VOUT = 1 .263 • 1 +
− 0 .5 µ A • R1
R
2
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SC1548
POWER MANAGEMENT
Applications Infomation (Cont.)
Please see Table 1 below for recommended resistor
values for some standard output voltages. All resistors
are 1%, 1/10W.
VOU T (V)
R 1 (Ω)
R 2 (Ω)
1.5
18.7
100
1.8
42.2
100
2.5
97.6
100
2.8
124
102
3.0
140
102
3.3
169
105
To be most effective, the MOSFET RDS(ON) should not be
selected artificially low. The MOSFET should be
chosen so that at maximum required current, it is almost
fully turned on. If, for example, a supply of 1.5V at 4A is
required from a 3.3V ± 5% rail, the maximum allowable
RDS(ON) would be:
R DS ( ON )( MAX ) =
4
To allow for temperature effects 200mΩ would be a
suitable room temperature maximum, allowing a peak
short circuit current of approximately 15A for a short time
before shutdown.
Capacitor Selection
Table 1: Recommended Resistor Values For SC1548
Output Capacitors: low ESR aluminum electrolytic or tantalum capacitors are recommended for bulk
capacitance, with ceramic bypass capacitors for
decoupling high frequency transients.
The maximum output voltage that can be obtained from
the adjustable option is determined by the input supply
voltage and the RDS(ON) and gate threshold voltage of the
external MOSFET. Assuming that the MOSFET gate
threshold voltage is sufficiently low for the output
voltage chosen and a worst-case drive voltage of 9V,
VOUT(MAX) is given by:
Input Capacitors: placement of low ESR aluminum
electrolytic or tantalum capacitors at the input to the
MOSFET (VPWR) will help to hold up the power supply
during fast load changes, thus improving overall transient
response. The 12V supply should be bypassed with a
0.1µF ceramic capacitor.
V OUT ( MAX ) = V PWR ( MIN ) − I OUT ( MAX ) • R DS ( ON )( MAX )
Short Circuit Protection
Layout Guidelines
The short circuit protection feature of the SC1548 is
implemented by using the RDS(ON) of the MOSFET. As the
output current increases, the regulation loop maintains
the output voltage by turning the FET on more and more.
Eventually, as the RDS(ON) limit is reached, the MOSFET
will be unable to turn on any further, and the output
voltage will start to fall. When the output voltage falls to
approximately 50% of nominal, the LDO controller is
latched off, setting output voltage to 0V. Toggling the
enable pin or cycling the power will reset the latch.
One of the advantages of using the SC1548 to drive an
external MOSFET is that the bandgap reference and
control circuitry do not need to be located right next to
the power device, thus a very accurate output voltage
can be obtained since heating effects will be minimal.
The 0.1µF bypass capacitor should be located close to
the supply pin, and connected directly to the ground plane.
The ground pin of the device should also be connected
directly to the ground plane. The sense or adjust pin does
not need to be close to the output voltage plane, but
should be routed to avoid noisy traces if at all possible.
To prevent false latching due to capacitor inrush currents
or low supply rails, the current limit latch is initially
disabled. It is enabled at a preset time (nominally 5ms)
after both IN and EN rise above their lockout points. If
EN is left floating (using the internal resistor pullup), then
VPWR should come up before VIN, or the device will latch
off. If the enable function is not being used, EN should
be tied to VPWR.
2004 Semtech Corp.
(0 .95 • 3 .3 − 1 .5 • 1 .025 ) ≈ 400 m Ω
Power dissipation within the device is practically
negligible, requiring no special consideration during
layout.
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SC1548
POWER MANAGEMENT
Outline Drawing - SOT-23-5
A
DIM
e1
D
A
A1
A2
b
c
D
E1
E
e
e1
L
L1
N
01
aaa
bbb
ccc
N
2X E/2
E
EI
1
2
ccc C
2X N/2 TIPS
e
B
D
aaa C
A2
DIMENSIONS
INCHES
MILLIMETERS
MIN NOM MAX MIN NOM MAX
.035
.000
.035
.010
.003
.110
.060
-
.045
-
.057
.006
.051
.020
.009
.118
.069
0.90
0.00
.90
0.25
0.08
2.80
1.50
-
1.15
-
1.45
0.15
1.30
0.50
0.22
3.00
1.75
2.90
1.60
2.80 BSC
0.95 BSC
1.90 BSC
0.30 0.45 0.60
(0.60)
5
0°
10°
0.10
0.20
0.20
.114
.063
.110 BSC
.037 BSC
.075 BSC
.012 .018 .024
(.024)
5
0°
10°
.004
.008
.008
A
SEATING PLANE
A1
C
H
bxN
bbb
C A-B D
c
GAGE
PLANE
0.25
L
01
(L1)
SEE DETAIL
DETAIL
A
A
SIDE VIEW
NOTES:
1.
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -H3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS
OR GATE BURRS.
Land Pattern - SOT-23-5
X
DIM
(C)
G
Z
Y
P
C
G
P
X
Y
Z
DIMENSIONS
MILLIMETERS
INCHES
(.098)
.055
.037
.024
.043
.141
(2.50)
1.40
0.95
0.60
1.10
3.60
NOTES:
1.
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
Contact Information
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
2004 Semtech Corp.
14
www.semtech.com
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