EXAR SP4446

SP4446
High Output Voltage Boost Regulator
LCD Bias Regulator
FEATURES
■ High Output Voltage: Up to 30V
■ High Efficiency
■ Low Quiescent Current: ~20uA
■ Single Battery Cell Operation
■ Programmable Output Voltage
■ 1Ω Switch (150mV at 150mA)
■ Lead Free, RoHS Compliant
Package: 5 Pin SOT-23
VIN
SHDN
5
4
SP4446
5 Pin SOT-23
1
2
3
SW
GND
FB
APPLICATIONS
■ LCD Bias
■ Tuner Pin Voltage
■ White LED Driver
■ High Voltage Bias
■ Digital Cameras
■ Cell Phone
■ Battery Backup
■ Handheld Computers
DESCRIPTION
The SP4446 is a micro power Boost Regulator in a 5-lead SOT-23 package. It is a current
limited, fixed off-time regulator configured for use in boost mode applications. The operating
voltage can be less than 3Volts and is capable of generating voltages as high as 30Volts.
The SP4446 is available in a Lead Free, RoHS compliant package and permits the construction
of complete regulators that occupy < 0.2 square inches of board space.
TYPICAL APPLICATION SCHEMATIC
L1
VIN
2 to 7V
D1
High
Voltage Output
10µH
VIN
SW
R1
C2
SP4446
SHDN GND
2.2 µF
FB
C1
R2
4.7µF
Mar28-08
SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator
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© 2008 Exar Corporation
ABSOLUTE MAXIMUM RATINGS
Lead Temperature (Soldering, 10 sec) ............ 300°C
ESD Rating ................................................. 2kV HBM
VIN ....................................................................... 15V
SW Voltage .............................................. -0.4 to 34V
FB Voltage .......................................................... 2.5V
All other pins .................................. -0.3 to VCC + 0.3V
Current into FB ................................................. ±1mA
TJ Max ............................................................. 125°C
Operating Temperature Range ............ -40°C to 85°C
Peak Output Current < 10us SW .................... 500mA
Storage Temperature ...................... -65°C to +150°C
Power Dissipation. ......................................... 200mW
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 specifications
below is not implied. Exposure to absolute maximum
rating conditions for extended periods of time may affect
reliability.
ELECTRICAL CHARACTERISTICS
Specifications are at VIN = 3.3V, VSHDN = VIN, TA = 25°C, ♦ denotes the specifications which apply over the full operating
temperature range, unless otherwise specified.
PARAMETER
SYMBOL MIN
Input voltage
VIN
Supply Current
IQ
Reference Voltage
VFB
FB Hysteresis
TYP
1.0
1.17
MAX UNITS
8.0
V
20
30
µA
0.01
1
µA
1.22
1.27
V
HYST
8
IFB
15
Line Regulation
∆Vo/∆VI
0.04
%/V
Switch Off Time
TOFF
300
nS
VFB Input Bias Current
Switch Saturation Voltage
VCESAT
Switch Current Limit
ILIM
SHDN Bias Current
ISHDN
SHDN High Threshold (on)
VIH
SHDN Low Threshold (off)
Switch Leakage Current
100
Switch Current Limit =
150mA
♦
No Switching
SHDN = 0.0V
♦
mV
80
nA
1200
nS
50
mV
150
mV
♦
VFB = 1.22V
1.2 ≤ VIN ≤ 8V
VFB > 1V
VFB < 0.3V
♦
ISW = 50mA
ISW = 150mA
150
200
mA
♦
5
12
µA
♦
VSHDN = 5V
♦
Switch Off, VSW = 5V
0.9
V
VIL
ISWLK
CONDITIONS
2
0.25
V
5
µA
PIN DESCRIPTION
PIN NUMBER
PIN NAME
1
SW
2
GND
Mar28-08
3
FB
4
SHDN
5
VIN
DESCRIPTION
Switch input to the internal power switch.
Ground
Feedback
Shutdown. Pull high (on) to enable. Pull low (off) for shutdown.
Input Voltage. Bypass this pin with a capacitor as close to the device
as possible.
SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator
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© 2008 Exar Corporation
FUNCTIONAL DIAGRAM
L1
VOUT
D1
VI
VIN
5
C1
SW
1
C2
(EXTERNAL)
R6
R5
R1
X1
DISABLE
+
Q1
POWER
TRANSISTOR
SET
Q2
300ns
ONE-SHOT
3
FB
(EXTERNAL)
CLEAR
R3
X2
R2
DRIVER
+
-
R4
SHDN
4
52.5mV
0.35
GND
Shutdown
Logic
2
THEORY OF OPERATION
General Overview:
At the end of the 0.3µs time period, the driver
transistor is again allowed to turn on which
ramps the current back up to the 150mA level.
Comparator X2 clears the latch, its output turns
off the driver transistor, and this allows delivery
of inductor L1’s stored kinetic energy to C2.
This switching action continues until the output
capacitor voltage is charged to the point where
FB is at band gap (1.22V). When this condition
is reached, X1 turns off the internal circuitry and
the cycle repeats. The SP4446 contains circuitry
to provide protection during startup and while in
short-circuit conditions. When FB pin voltage is
less than approximately 300mV, the switch off
time is increased to about 1.2µs and the current
limit is reduced to about 70% of its normal
value. While in this mode, the average inductor
current is reduced and helps minimize power
dissipation in the SP4446, the external inductor
and diode.
Operation can be best understood by referring to
the above block diagram. Q1 and Q2 along with
R3 and R4 form a band gap reference. The input
to this circuit completes a feedback path from
the high voltage output through a voltage divider, and is used as the regulation control input.
When the voltage at the FB pin is slightly above
1.22V, comparator X1 disables most of the
internal circuitry. Current is then provided by
capacitor C2, which slowly discharges until the
voltage at the FB pin drops below the lower
hysteresis point of X1, about 6mV. X1 then
enables the internal circuitry, turns on chip
power, and the current in the inductor begins to
ramp up. When the current through the driver
transistor reaches about 150mA, comparator X2
clears the latch, which turns off the driver transistor for a preset 0.3µs. At the instant of shutoff,
inductor current is diverted to the output through
diode D1. During this 0.3µs time limit, inductor
current decreases while its energy charges C2.
Mar28-08
SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator
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© 2008 Exar Corporation
APPLICATION INFORMATION
inherently low ESR, which will help produce low
peak to peak output ripple, and reduce high frequency spikes.
For the typical application, a 4.7µF input capacitor
and a 2.2µF output capacitor are sufficient. The
input and output ripple could be further reduced by
increasing the value of the input and output capacitors. Place all the capacitors as close to the SP4446
as possible for layout. For use as a voltage source,
to reduce the output ripple, a small feedforward
capacitor (47pF) across the top feedback resistor
can be used to provide sufficient overdrive for the
error comparator, thus reduce the output ripple.
Refer to Table 2 for some suggested low ESR capacitors.
Inductor Selection
For SP4446, the internal switch will be turned off
only after the inductor current reaches the typical
DC current limit (ILIM=150mA). However, there is
typically a propagation delay of 200nS between
the time when the current limit is reached and
when the switch is actually turned off. During this
200nS delay, the peak inductor current will increase, exceeding the current limit by a small amount.
The peak inductor current can be estimated by:
V
IPK = ILIM + IN(MAX) • 200nS
L
The larger the input voltage and the lower the
inductor value, the greater the peak current.
In selecting an inductor, the saturation current
specified for the inductor needs to be greater than
the SP4446 peak current to avoid saturating the
inductor, which would result in a loss of efficiency
and could damage the inductor. Choosing an inductor with low DCR decreases power losses and
increase efficiency.
Refer to Table 1 for some suggested low ESR inductors.
MANUF.
PART NUMBER
DCR
(Ω)
Current
Rating
(mA)
MURATA
770-436-1300
LQH32CN100K21
(10µH)
0.44
300
MURATA
770-436-1300
LQH32CN220K21
(22µH)
0.71
250
TDK
847-803-6100
NLFC453232T-100K
(10µH)
0.273
250
TDK
847-803-6100
NLC453232T-100K
(22µH)
0.9
MANUF.
PART
NUMBER
CAP/
VOLTAGE
SIZE/
TYPE
MURATA
770-436-1300
GRM32RR71E
225KC01B
2.2µF/25V
1210/X5R
MURATA
770-436-1300
GRM31CR61A
475KA01B
4.7µF/10V
1206/X5R
TDK
847-803-6100
C3225X7R1E
225M
2.2µF/25V
1206/X7R
TDK
847-803-6100
C3216X5R1A
475K
4.7µF/10V
1206/X5R
Table 2. Suggested Low ESR Capacitor
Output Voltage Program
In order for the SP4446 to be programmed as a
voltage source, the SP4446 requires 2 feedback
resistors R1 & R2 to control the output voltage, as
shown in Figure 1.
370
Table 1. Suggested Low ESR inductors
VIN
D1
L1
Diode Selection
VOUT
A schottky diode with a low forward drop and fast
switching speed is ideally used here to achieve
high efficiency. In selecting a Schottky diode, the
current rating of the schottky diode should be
larger than the peak inductor current. Moreover,
the reverse breakdown voltage of the Schottky
diode should be larger than the output voltage.
C2
U1
5
VI N
4
1
SW
SP4446
SHDN
FB
G ND
3
1.22V
R2
2
Capacitor Selection
Ceramic capacitors are recommended for their
Figure 1. Using SP4446 as Voltage Source
Mar28-08
R1
C1
SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator
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© 2008 Exar Corporation
APPLICATION INFORMATION: Continued
Two Resistors (R1=1MΩ, R2=42.2KΩ) are used
to program the output voltage to be 30V. When
input voltage is 3.3V or 5V, it can supply a
maximum current of 3mA and 5mA to the load.
The formula and table for the resistor selection
are shown below:
VOUT
R 1 =(
1.22
- 1 ) • R2
Load Disconnect in Shutdown
VOUT (V)
R1 (Ω)
R2 (Ω)
12
1M
113K
15
1M
88.7K
18
1M
73.2K
When SP4446 is shut down, the load is still
connected to the input. In applications that require output isolation during shutdown, an external PNP transistor (for example MMBT2907A)
can be added as shown in Figure 3.
R3
154K
20
1M
64.9K
30
1M
42.2K
L1
10uH
VIN
C1
4.7uF
Table 3. Divider Resistor Selection
U1
5
VIN
4
SHDN_N
DS
R1
1
SW
SP4446
SHDN
FB
GND
Q1
MMBT2907A
1M
VOUT
C2
47pF
C3
2.2uF
3
1.22V
R2
64.9K
Layout Considerations
2
Both the input capacitor and the output capacitor
should be placed as close as possible to the IC. This
can reduce the copper trace resistance which directly effects the input and output ripple. The
feedback resistor network should be kept close to
the FB pin to minimize copper trace connections
that can inject noise into the system. The ground
connection for the feedback resistor network should
connect directly to the GND pin or to an analog
ground plane that is tied directly to the GND pin.
The inductor and the Schottky diode should be
placed as close as possible to the switch pin to
minimize the noise coupling to the other circuits,
especially the feedback network.
Fig. 3. Load Disconnect in Shutdown
When the SP4446 is active, the voltage set at the
emitter of the transistor exceeds the input voltage, forcing the transistor into the saturation
region. When the SP4446 is shut down, the input
voltage exceeds the emitter voltage, thus the
transistor becomes inactive and provides highimpedance isolation between the input and load.
Efficiency will be slightly sacrificed because of
the saturation voltage and base current of the PNP
transistor.
PIN Diode Driver
The SP4446 can be used as PIN diode driver as
shown in Figure. 2.
Murata LQH32CN100K21
30V VOUT
DS
L1 10uH 0.3A
VIN
3.3V or 5V
3 to 5 mA
MBR0530
C2
47pF
C1
4.7uF
R1
1M
U1
5
VIN
4
C3
2.2uF
1
SW
SP4446
SHDN
FB
GND
2
3
1.22V
R2
42.2K
Fig. 2. Pin Diode Driver
Aug15-07
20V
SP4446 High Output Voltage Boost Regualtor, LCD Bias Regulator
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© 2007 Sipex Corporation
PERFORMANCE CHARACTERISTICS
Refer to the typical application circuit, TAMB = 25°C, unless otherwise specified.
Vin=3.3V;Vout =12V Efficiency
Vin=5.0V;Vout =12V Efficiency
85
85
80
80
75
Efficiency (%)
75
Efficiency (%)
70
65
60
70
65
60
55
10 uH
10 uH
55
22 uH
22 uH
50
50
0
3
6
9
Iout (mA)
12
15
18
0
5
15
20
25
Figure 5. 12V Output Efficiency (VIN=5V)
Vin=3.3V;Vout =15V Efficiency
Vin=5.0V;Vout =15V Efficiency
80
75
75
70
70
Efficiency (%)
80
65
60
65
60
55
55
10 uH
10 uH
22 uH
22 uH
50
0
2
4
6
Iout (mA)
8
10
50
12
0
Figure 6. 15V Output Efficiency (VIN=3.3V)
3
Vin=3.3V; Vout = 18V Efficiency
9
Iout (mA)
12
15
18
Vin=5.0V; Vout = 18V Efficiency
80
75
75
70
70
65
Efficiency (%)
Efficiency (%)
6
Figure 7. 15V Output Efficiency (VIN=5V)
80
60
55
50
65
60
55
50
10 uH
45
10 uH
45
22 uH
40
22 uH
40
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0.0
2.0
4.0
Iout (mA)
Figure 8. 18V Output Efficiency (VIN=3.3V)
Mar28-08
30
Iout (mA)
Figure 4. 12V Output Efficiency (VIN=3.3V)
Efficiency (%)
10
6.0
8.0
Iout (mA)
10.0
12.0
14.0
Figure 9. 18V Output Efficiency (VIN=5V)
SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator
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© 2008 Exar Corporation
PERFORMANCE CHARACTERISTICS
Refer to the typical application circuit, TAMB = 25°C, unless otherwise specified.
Vin=3.3V;Vout = 20V Efficiency
Vin=5V;Vout = 20V Efficiency
75
75
70
70
65
65
Efficiency (%)
Efficiency (%)
60
55
50
60
55
50
45
45
40
10 uH
10 uH
40
35
22 uH
22 uH
35
30
0
1
2
3
4
5
6
0
7
2
4
6
Figure 10. 20V Output Efficiency (VIN=3.3V)
10
12
Figure 11. 20V Output Efficiency (VIN=5V)
12
6
10uH
10
10uH
22uH
5
Maximum Output Current (mA)
Maximum Output Current (mA)
8
Iout (mA)
Iout (mA)
8
6
4
22uH
4
3
2
2
1
0
2.7
3
3.3
3.6
3.9
4.2
4.5
4.8
0
2.7
5.1
3
3.3
3.6
Input Voltage (V)
Figure 12. Maximum Output Current vs. V IN (V OUT=20V)
4.2
4.5
4.8
5.1
Figure 13. Maximum Output Current vs. VIN (VOUT=30V)
10
30
25
8
Shutdown Pin Current (uA)
Quiescent Current (uA)
3.9
Input Voltage (V)
20
15
10
Tamb=-40°C
5
6
4
2
Tamb=25°C
Tamb=85°C
0
0
1
2
3
4
5
6
7
1
8
2
Input Voltage (V)
4
5
6
7
Input Voltage (V)
Figure 14. Quiescent Current IQ vs. VIN
Mar28-08
3
Figure 15. Shutdown Pin Current vs. VIN
SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator
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© 2008 Exar Corporation
8
PERFORMANCE CHARACTERISTICS
Refer to the typical application circuit, TAMB = 25°C, unless otherwise specified.
250
1.25
1.24
200
Feedback Voltage (V)
Ipk Current Limit (mA)
1.23
150
100
1.22
1.21
1.20
50
1.19
0
1
2
3
4
5
6
7
1.18
-40
8
-15
10
35
60
85
Temperature (C)
Input Voltage (V)
Figure 16. IPK Current Limit vs. VIN
Figure 17. Feedback Voltage vs. Temperature
60
Switch Saturation Voltage (mV)
50
VIN
40
30
20
VOUT
10
0
-40
IIN (100mA/DIV)
-15
10
35
60
85
Temperature (C)
Figure 19. Startup Waveform (VIN=3.3V, VOUT=20V,
IOUT=2mA)
Figure 18. Switch Saturation Voltage VCESAT vs.
Temperature (ISW=50mA)
VSW
IOUT (5mA/DIV)
VOUT (AC)
IL (0.1A/DIV)
VOUT (AC)
VSW
Figure 21. Load Step Transient (VIN=3.3V, VOUT=20V,
1O=100µA∼5mA)
Figure 20. Typical Switching Waveforms (VIN=3.3V,
VOUT=20V, IOUT=5mA)
Mar28-08
SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator
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© 2008 Exar Corporation
PACKAGE: 5 PIN SOT-23
Mar28-08
SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator
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© 2008 Exar Corporation
ORDERING INFORMATION
Part Number
Operating Temperature Range
Package Type
SP4446EK-L .................................................. -40°C to +85°C ...................................Lead Free 5 Pin SOT-23
SP4446EK-L/TR ............................................ -40°C to +85°C ...................................Lead Free 5 Pin SOT-23
-G: “Green”/Halogen free package. Substitute “-L” by “-G” in the ordering part number.
/TR = Tape and Reel
Pack quantity is 2,500 for SOT-23.
Exar Corporation
Headquarters and
Sales Office
248720 Kato Rd,33 South Hillview Drive
M Fremont, CA 94538
TEL: (510) 668-7000
FAX: (510) 668-7001
Exar Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the
application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others.
Mar28-08
SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator
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© 2008 Exar Corporation