®
SP6231
500mA, 3.3V Linear Regulator with Auxiliary Backup
FEATURES
■
“Tiny” DFN Package Offers Excellent Thermal
Characteristics (also available in NSOIC)
■
“Glitch Free” Transition between Two Supplies
■
3.3V Fixed LDO Output Voltage
■
400µA Quiescent Current @500mA Load
■
Fast Transient Response
■
Current Limit Protection
■
Thermal Shutdown Protection with Hysteresis
■
Auxiliary Supply Control
■
Internal 0.2Ω PFET Switch Eliminates External
FETs
■
Kelvin Connection with 3.3V Feedback
V
ENSE
1
S
V
IN
2
V
OUT
3
V
AUX
4
8 GND
SP6231
8 Pin NSOIC
7 GND
6 GND
5 GND
Now Available in Lead Free Packaging
APPLICATIONS
■
USB Peripherals
■
NIC Cards
■
PCMCIA/PCI Cards
■
Desktop Computers
■
Dual Power Systems
DESCRIPTION
The SP6231 is a 500mA, 3.3V LDO with an integrated auxiliary voltage input switch. During
normal operation, the SP6231 acts as a standard LDO with an output voltage of 3.3V delivering
up to 500mA. When the 5V input drops below 4.4V, the 3.3V, V
AUX
input is switched to the output
through an internal PFET, maintaining a constant “glitch free” output voltage.
The SP6231 is ideally suited for NIC cards and portable battery powered equipment. When a
desktop computer reverts to sleep mode, its 5V bus is removed, leaving only the 3.3V bus. The
SP6231’s auxiliary output passes the 3.3V bus through, keeping the NIC card available for any
Wake-On-LAN command. In battery powered applications, the SP6231 draws power from any
available 5V USB connection and reverts to battery power when the USB power is removed.
TYPICAL APPLICATION CIRCUIT
+5V USB
C1
2.2µF
+3.3V
AUX
C2
2.2µF
GND
GND
V
AUX
OUT
C3
10µF
GND
V
OUT
3.3V
@ 500mA
V
IN
SP6231
V
SENSE
Date: 5/25/04
SP6231 500mA, 3.3V Linear Regulator
© Copyright 2004 Sipex Corporation
1
ABSOLUTE MAXIMUM RATINGS
V
IN .........................................................................................
0.3V to 7V
V
OUT .....................................................................................
0.3V to 6V
V
AUX .....................................................................................
0.3V to 7V
Storage Temperature ........................ -65°C to 150°C
Power Dissipation ............................ internally limited
Lead Temperature (Soldering) .... 60 sec. max above
183°C,230°C Peak
These are stress ratings only and functional operation
of the device at these ratings or any other above those
indicated in the operation sections of the specifica-
tions below is not implied. Exposure to absolute
maximum rating conditions for extended periods of
time may affect reliability.
ELECTRICAL CHARACTERISTICS
Unless otherwise specified: -40°C < T
A
< 85°C, 4.75V≤ V
IN
< 6V, C
OUT
≥
10µF with ESR <1Ω, I
OUT
= 10mA,
V
AUX
= 3.3V
PARAMETER
LINEAR REGULATOR
Output Voltage
Line Regulation
Load Regulation
Ground Current
Current Limit
Thermal Shutdown
Thermal Shutdown
Hysteresis
V
SENSE
Pin Current
AUXILIARY BACKUP
Upper V
IN
Threshold
Lower V
IN
Threshold
V
IN
Threshold Hysteresis
Ground Current
R
DS(ON)
Current Limit
Maximum Junction
Temperature, T
J(MAX)
Thermal Resistance,
θ
JA
V
V
mV
µA
Ω
A
°C
°C/W
57
4.35
4.25
4.5
4.4
100
40
0.2
1.1
125
DFN package
0.4
V
IN
< 4.25V, V
AUX
= 3.3V,
I
OUT
= 0mA
V
IN
< 4.25V,V
AUX
= 3.3V,
I
OUT
= 500mA
0V < V
OUT
< 3.2V
4.65
4.55
V
IN
increasing
V
IN
decreasing
V
mV
mV
µA
µA
A
°C
°C
µA
0.55
140
3.200
3.300
1
5
110
400
1.0
165
15
15
1.5
3.400
5
25
10mA < I
OUT
< 500mA
V
IN
= 4.75V to 6V
V
IN
= 5V,
I
OUT
= 10mA to 500mA
I
OUT
= 10mA
I
OUT
= 500mA
0V < V
OUT
< 3.2V
V
IN
= 5V or V
IN
= 0V
UNITS
MIN
TYP
MAX
CONDITIONS
Date: 5/25/04
SP6231 500mA, 3.3V Linear Regulator
© Copyright 2004 Sipex Corporation
2
THEORY OF OPERATION
General Overview
The SP6231 combines a linear regulator with an
auxiliary backup. When the main supply volt-
age is applied at V
IN
, the SP6231 acts as a
regulator. It supplies 3.3V at its output and
sources up to 500mA with an overall accuracy
of
±3%.
Full protection with both current limit
and thermal shutdown is provided. When the
main supply drops below 4.4V, the output is
switched through an internal PFET to the auxil-
iary supply input.
A typical application is a USB peripheral (for
instance a digital camera) that in normal opera-
tion draws power from a battery supply (V
AUX
)
but when it is plugged into the USB port will
recognize the main power supply availability
(V
IN
) and draw its power from there, switching
over from the battery to the main power supply.
When the USB peripheral is removed from the
USB port, the output is switched back “glitch
free” to the battery supply so the peripheral sees
no supply interruption. Other applications in-
clude NIC cards, desktop computers, power
supplies with multiple input sources and
PCMCIA/PCI interface cards.
Modes of Operation
There are 2 modes of operation. The first mode
is the LDO mode when the main supply (V
IN
) is
above 4.5V. At this point (independent of what
voltage the auxiliary supply is at) the SP6231
acts as an LDO with an output of 3.3V capable
of delivering up to 500mA. In this mode all
circuitry is powered off of the main supply V
IN
.
The second mode, the backup switch mode,
occurs when V
IN
drops below the auxiliary
supply (and below the 4.4V LDO mode). In this
mode the output is directly connected to the
auxiliary input through an internal 0.2Ω PFET
switch. All circuitry is powered off of the aux-
iliary supply. When the main supply is below
4.4V but still greater then the auxiliary supply,
the output is connected to the auxiliary supply
but most internal circuitry is still powered off of
the main supply. How this effects quiescent
currents can be seen in Figure 1.
120
I
IN
I
AUX
Quiescent Currents (µA)
100
80
60
40
20
0
0
1
2
3
4
5
6
V
IN
(V)
Figure 1. Ground pin current vs. input voltage
(V
AUX
= 3.3V, no load)
Linear Regulator Mode
When the main supply of the SP6231 (V
IN
) is
above 4.5V, the part is in linear regulated LDO
mode (regardless of the auxiliary supply level).
It sources 3.3V (±3%) up to 500mA.
+3.3V Auxiliary Switch Mode
When the main supply falls below 4.4V, the
output is connected to the auxiliary supply
through an internal 0.2Ω PFET switch.
Sense Pin
In the LDO mode, a sense pin provides a Kelvin
connection with a 3.3V feedback (always tie
this pin to the point of regulation). If an accurate
3.3V supply is needed some distance away from
the SP6231, a drop in voltage might occur due to
the resistance of the length of the trace from the
SP6231 to where the supply is needed. For a
0.5Ω trace carrying 500mA the drop would be
0.25V leaving 3.05V at the supply destination.
By Kelvin connecting the sense pin to the supply
destination the SP6231 will adjust its output
voltage (to 3.55V) so that the voltage is 3.3V at
the supply destination. If this accuracy is of no
concern, the sense pin can simply be tied to the
output pin. The sense pin draws 15µA of current.
Thermal and Overcurrent Protection
Both the LDO switch and the backup switch
have overcurrent and thermal protection. The
overcurrent protection will limit the output cur-
rent to 1A for the LDO and 0.8A for the backup
switch typically. When the SP6231 heats up
above 165°C (due to power consumption in the
chip), both switches will be opened so the part
can cool down. Once the temperature drops by
15°C, the SP6231 will turn on again.
Date: 5/25/04
SP6231 500mA, 3.3V Linear Regulator
© Copyright 2004 Sipex Corporation
4
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