SEMTECH SC1548CSK

SC1548
Linear Fet Controller
POWER MANAGEMENT
Description
Features
u ± 2.5% output accuracy over line, load and
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.
temperature
u 1.515V, 1.818V and adjustable output voltage
options available
u Enable control
u Over current protection
u 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.
u
u
u
u
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 1, January 2001
5
4
C4
0.1uF
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SC1548
POWER MANAGEMENT
Absolute Maximum Ratings
Parameter
Sy mbol
Maximum
U nits
VIN
-0.5 to +15
V
VADJ, VEN, VSNS
-0.5 to +7
V
Thermal Impedance Juncti on to C ase
q JC
81
°C /W
Thermal Impedance Juncti on to Ambi ent
q JA
256
°C /W
Operati ng Ambi ent Temperature Range
TA
0 to +70
°C
Operati ng Juncti on Temperature Range
TJ
0 to +125
°C
Storage Temperature Range
TSTG
-65 to +150
°C
Lead Temperature (Solderi ng) 10 Sec
TLEAD
300
°C
Input Supply Voltage
Input Pi ns
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
Sy mbol
Test C onditions
Min
Ty p
Max
U nits
11.28
12.00
12.72
V
1.0
1.5
mA
IN
Supply Voltage
VIN
Qui escent C urrent
IQ
2.0
U nderv oltage Lockout
Start Threshold
UVLO
7
8
9
V
100
150
µA
2.3
V
EN
Enable Pi n C urrent
IEN
V E N = 0V
Threshold Voltage
VTH(EN)
VEN ri si ng
Hysteresi s
VHYST
Enable D elay Ti me(2)(3)
tD(ON)
D i sable D elay Ti me(2)(3)
tD(OFF)
1.8
200
mV
VEN = Low to Hi gh, measured from
VEN = VTH(EN) to 10% VDRV
500
ns
VEN = Hi gh to Low, measured from
VEN = VTH(EN) to 90% VDRV
150
ns
SN S (Fixed Output Voltage Parts)
Sense Pi n C urrent
ISNS
Si nki ng
75
100
125
µA
AD J (Adjustable Output Voltage Parts)
Adjust Pi n C urrent
IADJ
Sourci ng
Reference Voltage(2)
V AD J
3.0V £ VPWR(4) £ 3.6V, 1mA £ IOUT £ 1A
0.25
-1.5%
-2.5%
ã 2001 Semtech Corp.
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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
Sy mbol
Test C onditions
Min
Ty p
Max
U nits
-1.5%
VOUT
+1.5%
V
Output Voltage R egulation (Fixed Output Voltage Parts)
Output Voltage(2)
VOUT
3.0V £ VPWR(4) £ 3.6V, 1mA £ IOUT £ 1A
-2.5%
+2.5%
DRV
Output C urrent
IDRV
VDRV = 4V, VSNS = 1.2V
5
10
mA
Output Voltage
VDRV
Full On, IDRV = 0mA
9.0
10.5
V
Ri se Ti me(2)(3)
tr
VEN = Low to Hi gh, measured from
VEN = VTH(EN) to 90% VDRV
1.0
ms
Fall Ti me(2)(3)
tf
VEN = Hi gh to Low, measured from
VEN = VTH(EN) to 10% VDRV
550
µs
Ov ercurrent Protection
Tri p Threshold
VTH(OC)
Power-up Output Short
C i rcui t Immuni ty
Output Short C i rcui t Gli tch
Immuni ty
30
50
70
%VOUT
1
5
60
ms
0.5
4
10
ms
C ontrol Section
Bandwi dth
VDRV = 9V, THD = 5%, C L = 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.
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SC1548
POWER MANAGEMENT
Timing Diagram
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SC1548
POWER MANAGEMENT
Pin Configuration
Ordering Information
Top View
Part N umber(1)(2)
P ackag e
SC 1548C SK-X.X.TR
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.
SOT-23-5L
Block Diagram
Pin Descriptions
Pin
1
Pin N ame Pin Function
SNS
Regulator sense i nput for fi xed output voltage opti ons. 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. S et output voltage as follows (refer to
appli cati on ci rcui t on page 1):
R1 

VO = 1 . 263 •  1 +

R2 

2
GND
Ground.
3
D RV
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 desi red.
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.
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SC1548
POWER MANAGEMENT
Typical Characteristics(1)
Quiescent Current vs.
Start Threshold vs.
Junction Temperature
Junction Temperature
1000
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
125
0
25
50
TJ (°C)
Enable Threshold Voltage
Enable Hysteresis vs.
vs. Junction Temperature
Junction Temperature
2.30
125
100
125
100
125
VIN = 12V
VEN falling
450
2.20
400
2.15
350
VHYST (mV)
VTH(EN) (V)
100
500
VIN = 12V
VEN rising
2.25
2.10
2.05
2.00
300
250
200
1.95
150
1.90
100
1.85
50
1.80
0
0
25
50
75
100
125
0
25
50
TJ (°C)
150
75
TJ (°C)
Enable Pin Current vs.
Enable Delay Time vs.
Junction Temperature
Junction Temperature
1000
VIN = 12V
VEN = 0V
VIN = 12V
900
125
800
700
tD(ON) (ns)
100
IEN (µA)
75
TJ (°C)
75
50
600
500
400
300
200
25
100
0
0
0
25
50
75
100
125
0
TJ (°C)
ã 2001 Semtech Corp.
25
50
75
TJ (°C)
6
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SC1548
POWER MANAGEMENT
Typical Characteristics (Cont.)(1)
Disable Delay Time vs.
Sense Pin Current vs.
Junction Temperature
Junction Temperature
200
125
VIN = 12V
VIN = 12V
VEN = 3.3V
VSNS = VO(NOM)
120
175
115
150
ISNS (µA)
tD(OFF) (ns)
110
125
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
100
OCP Trip Threshold (SC1548CSK-1.8)
Power-Up Output Short Circuit Immunity
vs. Junction Temperature
vs. Junction Temperature
125
10
Power-up Short Circuit Immunity (ms)
VIN = 12V
VEN = 3.3V
1
0.8
VTH(OC) (V)
75
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
0
125
ã 2001 Semtech Corp.
25
50
75
100
125
TJ (°C)
TJ (°C)
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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
50
75
100
TJ (°C)
Drive Pin Fall Time vs.
SC1548CSK-1.8 Small Signal Gain
Junction Temperature
and Phase Shift vs. Frequency
80
1000
800
0
IOUT = 1.8A
VIN = 12V
VEN switched from 3.3V to 0V
Two representative parts shown
900
60
-45
40
-90
700
Gain
f (Hz)
600
tf (µs)
125
TJ (°C)
500
400
20
-135
0
-180
-20
-225
-40
-270
Phase (°)
Short Circuit Glitch Immunity (ms)
8
300
200
-60
100
0
25
50
75
100
-80
1.00E+02
125
1.00E+03
TJ (°C)
1.00E+04
-360
1.00E+06
1.00E+05
Gain (dB)
SC1548CSK-1.5 Small Signal Gain
SC1548CSK Small Signal Gain
and Phase Shift vs. Frequency
and Phase Shift vs. Frequency
80
80
0
0
IOUT = 1.8A
VOUT = 2V
IOUT = 1.8A
60
60
-45
40
-90
40
-180
-20
-225
-40
-270
-60
Phase
1.00E+03
ã 2001 Semtech Corp.
1.00E+04
f (Hz)
1.00E+05
Gain (dB)
0
Phase (°)
Gain (dB)
-135
-45
-90
Gain
Gain
20
-80
1.00E+02
-315
20
-135
0
-180
-20
-225
Phase (°)
0
Phase
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
ã 2001 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.
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Output Voltage
R 1 (kW)
R 1 (kW)
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.
ã 2001 Semtech Corp.
R2 ≤
1 . 263 V
50 µ A
Ω
The output voltage can be calculated as follows:
R1 

V OUT = 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.
V OU T (V )
R 1 (W)
R 2 (W)
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 ) =
Capacitor Selection
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:
( MIN )
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.
− 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. Power must be
cycled to 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.
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To allow for temperature effects 200mW would be a
suitable room temperature maximum, allowing a peak
short circuit current of approximately 15A for a short time
before shutdown.
Table 1: Recommended Resistor Values For SC1548
V OUT ( MAX ) = V PWR
(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
Land Pattern - SOT-23-5
Contact Information
Semtech Corporation
Power Management Products Division
652 Mitchell Rd., Newbury Park, CA 91320
Phone: (805)498-2111 FAX (805)498-3804
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