200mA & 250mA SmartLDOs
TM
POWER MANAGEMENT
Description
The SC1531(A) is designed to maintain a glitch-free 3.3V
output when at least one of two inputs, 5V (VIN) and
3.3V (VAUX), is present.
SC1531(A)
Features
Glitch-free transition between input sources
Internal logic selects input source
Gate drive for external PMOS bypass switch
5V detection with hysteresis
1% regulated output voltage accuracy
200mA load current capability
(250mA for SC1531A)
Remote sense
SO-8 package
u
u
u
u
Whenever VIN exceeds a predetermined threshold value,
u
the internal 3.3V linear regulator is enabled, and DR is
u
pulled high.
u
When VIN falls below a lower threshold value, DR is pulled
u
low and the internal linear regulator is turned off. DR has
been designed to drive the gate of an external low
threshold P-channel MOSFET, which can be used to
connect the 3.3V supply directly to the regulator output.
This ensures an uninterrupted 3.3V output even if VIN
falls out of specification. A typical R
DS(ON)
of 400mW is
recommended (320mW for SC1531A).
When both supplies are simultaneously available, the
drive pin (DR) will be pulled High, turning off the external
PMOS switch.
The internal 5V detector has its upper threshold (for VIN
rising) set to 4.18V (typical) while the lower threshold (for
VIN falling) is at 4.05V (typical) giving a hysteresis of
approximately 130mV.
The SENSE pin, which is connected to the load, connects
internally to the inverting input of the LDO error
amplifier. It enables tight regulation of the load voltage
(while the 5V supply is present) despite variations in load
current.
The SC1531(A) is available in the popular SO-8 surface
mount package.
Applications
u
u
u
u
u
Desktop Computers
Network Interface Cards (NICs)
PCMCIA/PCI Interface Cards
Cardbus
TM
Technology
Power supplies with multiple input sources
Typical Application Circuit
Notes for Typical Application Circuit:
(1) External switch (Q1): use Motorola MGSF1P02ELT1
or equivalent (PMOS, typical Gate Threshold Voltage =
1V, typical R
DS(ON)
= 0.4W at V
GS
= 2.5V) for SC1531. Use
Vishay Si2301DS or equivalent for SC1531A.
(2) Connection of VAUX (pin 3) is optional.
Q1
U1
5V
3.3V
1
2
3
4
C1
0.1uF
C2
4.7uF
C3
0.1uF
VIN
DR
NC
VO
VAUX SENSE
GND
NC
SC1531
8
7
6
5
C4
4.7uF
C5
0.1uF
3.3V OUT
Revision 1, December 2000
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SC1531(A)
POWER MANAGEMENT
Absolute Maximum Rating
Parameter
Input Supply Voltage
Auxi li ary Supply Voltage
LD O Output C urrent (SC 1531)
LD O Output C urrent (SC 1531A)
Thermal Impedance Juncti on to Ambi ent
Thermal Impedance Juncti on to C ase
Operati ng Ambi ent TemperatureRange
Operati ng Juncti on Temperature Range
Storage Temperature Range
Lead Temperature (Solderi ng) 10 Sec.
ESD Rati ng
Sy mbol
VIN
VAUX
I
O
I
O
q
JA
q
JC
T
A
T
J
T
STG
T
LEAD
V
ESD
Maximum
-0.5 to +7
-0.5 to +7
200
250
130
47
-5 to +70
-5 to +125
-65 to +150
300
2
U nits
V
V
mA
mA
°C /W
°C /W
°C
°C
°C
°C
kV
Electrical Characteristics
Unless specified: T
A
= 25°C, VIN = 5V, VAUX = 3.3V, I
O
= max. rated, C
O
= 4.7µF. Values in
bold
apply over full operating temperature range.
Parameter
VIN
Supply Voltage
Qui escent C urrent
Sy mbol
Test C onditions
Min
Ty p
Max
U nits
VIN
I
Q
VAUX = 0V
VIN = 5V, VAUX = 0V, I
O
= 0mA
4.3
5.0
7.0
5.5
10.0
11.0
V
mA
VIN = 5V, VAUX = 3.3V, I
O
= 0mA
7.5
10.0
12.0
mA
Reverse Leakage From VAUX
I
VIN
VAUX = 3.6V, VIN = 0V, I
O
= 0mA
1.0
10
20
µA
VAU X
Supply Voltage
Qui escent C urrent
VAUX
I
Q(AUX)
VAUX = 3.3V, VIN = 0V, I
O
= 0mA
3.0
3.3
0.8
3.6
1.5
2.0
VAUX = 3.3V, VIN = 5V, I
O
= 0mA
0.6
1.0
2.0
Reverse Leakage From VIN
I
VAUX
VIN = 5.5V, VAUX = 0V, I
O
= 0mA
7
50
100
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V
mA
mA
µA
SC1531(A)
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Unless specified: T
A
= 25°C, VIN = 5V, VAUX = 3.3V, I
O
= max. rated, C
O
= 4.7µF. Values in
bold
apply over full operating temperature range.
Parameter
5V D etect
(1)(2)(3)
Low Threshold Voltage
Hysteresi s
Sy mbol
Test C onditions
Min
Ty p
Max
U nits
V
TH(LO)
V
HYST
VIN Falli ng
3.90
90
80
4.05
200
4.20
V
mV
Hi gh Threshold Voltage
VO
LD O Output Voltage
V
TH(HI)
VIN Ri si ng
4.30
V
VO
I
O
= 20mA
4.3V
£
VIN
£
5.5V, 0mA
£
I
O
£
I
O(MAX)
3.9V
£
VIN
£
4.3V, VAUX = 3.3V,
0mA
£
I
O
£
I
O(MAX)(4)
3.267
3.234
3.000
3.300
3.333
3.366
V
Li ne Regulati on
REG
(LINE)
VIN = 4.3V to 5.5V
0.12
0.40
0.60
%
Load Regulati on
REG
(LOAD)
I
O
= 20mA to I
O(MAX)
0.12
0.40
0.60
%
SEN SE
SENSE Pi n Impedance
DR
D ri ve Voltage
V
DR
4.3V
£
VIN
£
5.5V, I
DR
= 200µA
3.4
3.3
VIN < V
TH(LO)
, I
DR
= -200µA
35
150
200
Peak D ri ve C urrent
I
DR(PK)
Si nki ng: VIN = 3.9V, V
DR
= 1V;
Sourci ng: VIN = 4.3V, (VIN - V
DR
) = 2V
D ri ve Hi gh D elay
(1)(5)
t
DH
C
DR
= 1.2nF, VIN rampi ng up, measured
from VIN = V
TH(HI)
to V
DR
= 2V
D ri ve Low D elay
(1)(5)
t
DL
C
DR
= 1.2nF, VIN rampi ng down, measured
from VIN = V
TH(LO)
to V
DR
= 2V
0.5
7
6
0.5
1.0
2.0
1.0
2.0
µs
µs
mA
mV
VIN - 0.8
V
R
SENSE
6.0
8.5
kW
See next page for
Notes.
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SC1531(A)
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Notes:
(1) Guaranteed by design.
(2) See 5V Detect Thresholds below.
(3) Recommended source impedance for 5V supply:
£
0.25W (0.2W for SC1531A). This will ensure that
I
O
x R
SOURCE
< V
HYST
, thus avoiding DR toggling during 5V detect threshold transitions.
(4) In Application Circuit on page 1.
(5) See Timing Diagram below.
5V Detect Thresholds
(1)
Note:
(1) VIN rise and fall times (10% to 90%) to be
³
100µs.
Timing Diagram
(1)
Note:
(1) VIN rise and fall times (10% to 90%) to be
£
100ns.
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SC1531(A)
POWER MANAGEMENT
Pin Configuration
(TOP VIEW)
Ordering Information
Part N umber
(1)
SC 1531C S.TR
SC 1531AC S.TR
Output C urrent
200mA
250mA
P ackag e
SO-8
SO-8
Note:
(1) Only available in tape and reel packaging. A reel
contains 2500 devices.
(SOIC-8)
Block Diagram
Pin Descriptions
Pin
1
2
3
4
5
6
7
8
Pin N ame
VIN
NC
VAUX
GND
NC
SENSE
VO
DR
Pin Function
Thi s i s the mai n i nput supply for the IC , nomi nally 5V.
No connecti on.
Thi s i s the auxi li ary i nput supply, nomi nally 3.3V. C onnecti on of thi s pi n i s opti onal, and wi ll sli ghtly
i mprove the turn-on ti me of the external MOSFET. Leave floati ng i f not used.
Logi c and power ground.
No connecti on.
Sense pi n for VO. C onnect to VO at the load to mi ni mi ze voltage drop across PC B traces. If
remote sense functi on i s not requi red, connect di rectly to pi n 7.
LD O 3.3V output.
D ri ver output for external P-channel MOSFET pass element.
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