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SS8028
Micro-Power Step-up DC/DC Converter
FEATURES
Configurable output voltage up to 16V Quiescent current of 20A Shutdown current <1A Shutdown-pin current <1A Supply range from 2.5V to 6.5V Low V DS(on): 250mV (ISW =300mA) Tiny SOT-23-5 package With a typical quiescent current of 20A and a supply voltage range of 2.5V to 6.5V, it is suitable for battery powered portable applications, such as PDAs and handheld computers. When the SS8028 goes into shutdown mode, it consumes less than 1A.
DESCRIPTION
The SS8028 boost converter is designed for small and medium size LCD panels requiring high bias voltages.
APPLICATIONS
* * * * * * * * STN/TFT LCD Bias Personal Digital Assistants (PDAs) Handheld Computers Digital Still Cameras Cellular Phones WebPad White LED Driver Local 3V to 5V Conversion
Furthermore, with a 350mA current limit, 500ns fixed minimum off-time and tiny SOT-23-5 package, the SS8028 can be used with smaller inductors and other surface-mount components to minimize the required PCB footprint in space-conscious applications. To control the SS8028, no other external current is needed for the shutdown pin, which typically consumes less than 1A over the full supply range.
TYPICAL APPLICATION CIRCUIT
10uH
16V 12mA
SW SW 1M
2.5V - 4.2V
VCC VCC
SS8028 G5111
SHDN SHDN 4.7F GND FB FB 1F 80.6k
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ORDERING INFORMATION
SS8028TXXXX Packing TR: Tape and reel TB: Tube Pinout option T11 Example: SS8028T11TR a T11 pin configuration shipped in tape and reel packing SOT-23-5 Top view
SW 1 GND 2 FB 3 VCC
PIN CONFIGURATION
SS8028T11
5
G963
4
SHDN
PIN DESCRIPTIONS
PIN
1 2 3 4 5
NAME
SW GND FB
SHDN
FUNCTION
Switch pin. The drain of the internal N-MOSFET power switch. Connect this pin to the inductor. Ground. Feedback pin. Set the output voltage by selecting values for R1 and R2 (see the Block Diagram): VOUT -1 R1 = R2 1. 2 Active-low shutdown pin. Tie this pin to logic-high to enable the device, or tie it to logic-low to turn the device off. Input supply pin. Bypass this pin with a capacitor as close to the device as possible.
VCC
ABSOLUTE MAXIMUM RATINGS
SW to GND.................................................................................-0.3V to +18V FB to GND..................................................................................-0.3V to VCC VCC, SHDN to GND..................................................................................-0.3V to +7V
Operating Temperature Range............................................................. -40C to 85C Maximum Operating Junction Temperature.................................................... +125C Storage Temperature Range .............................................................. -65C to 150C Maximum Lead Temperature (Soldering, 10sec)............................................ +300C
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ELECTRICAL CHARACTERISTICS
(VCC = 3.6V, V SHDN = 3.6V, TA = 25C)
PARAMETER Input Voltage Range
CONDITIONS
MIN 2.5
TYP MAX 6.5 20 0.1 30 1 1.22
UNITS V A A V %/V
Not switching Quiescent Current FB Comparator Trip Point Output Voltage Line Regulation FB Pin Bias Current (Note 2) Switch Off Time 2.5V 1V VFB < 0.6V ISW = 300mA 300 V SHDN = 0V 1.18
1.2 -0.05 30 500 1.6 250 350 0.1
80
nA ns s
Switch VDS(ON) Switch Current Limit
SHDN SHDN SHDN
350 400 1
mV mA A V
Pin Current Input Voltage High Input Voltage Low Switch off, VSW = 16V 0.9
0.25 0.01 5
V A
Switch Leakage Current
Note 1: The SS8028 is guaranteed to meet performance specifications from 0C to 85C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 2: Bias current flows into the FB pin.
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TYPICAL PERFORMANCE CHARACTERISTICS
(VCC=+3.6V, V SHDN =+3.6V, L=10H, TA=25C, unless otherwise noted.)
Efficiency vs. Load Current
90
VIN=4.2V VIN=3.6V VIN=2.7V VIN=2.7V
Output Voltage vs. Load Current
17
80 70 60 50 40
VOUT=16V
Output Voltage (V)
16.5
VIN=4.2V
Efficiency (%)
16
15.5
30
0.1 1 10 100
15
1 2 3 4 5 6 7 8 9 10
Load Current (mA)
Load Current (mA)
Vds_on vs. Temperature
500 50
Quiescent Current vs. Temperature
Quiescent Current (A)
Switch Vds_on (mV)
400 VIN=2.7V 300
40
30
VIN=4.2V
200 VIN=4.2V
20
VIN=2.7V
100
-20 0 20 40 60 80 100
10
-20 0 20 40 60 80 100
Temperature (C)
Temperature (C)
FB Bias Current vs. Temperature
30 1.22 VIN=2.7V
Feedback Voltage vs. Temperature
Feedback Bias Current (nA)
Feedback Voltage (V)
1.21 VIN=2.7V 1.2
25
20 VIN=4.2V
1.19
VIN=4.2V
15
-20 0 20 40 60 80 100
1.18
-20 0 20 40 60 80 100
Temperature (C)
Temperature (C)
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TYPICAL PERFORMANCE (cont.)
Switch Current Limit vs. Temperature
450
Load Transient
Peak Current (mA)
400
VIN=4.2V
350
VIN=2.7V
300
250
-20 0 20 40 60 80 100
Temperature (C)
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BLOCK DIAGRAM
L1 V IN C1 VCC SHDN SW C2 VOUT
BIAS VOUT
SHUTDOWN LOGIC PUMP CONTROL OC DRIVER COMP en_sw + T OFF P U L S E CONTROL
R1 +
ERROR COMP FB
R2
1.2 V
VREF
GND
APPLICATIONS INFORMATION
The SS8028 is a boost converter with an integrated N-channel MOSFET (refer to the block diagram above). The boost cycle is initiated when the FB pin voltage drops below 1.2V and the MOSFET turns on. During the period that the MOSFET is on, the inductor current ramps up until the 350mA current limit is reached. Then the MOSFET turns off and the inductor current flows through the external schottky diode, ramping down to zero. During the MOSFET off period, the inductor current charges the output capacitor and the output voltage climbs. This pumping mechanism continues cycle by cycle until the FB pin voltage exceeds 1.2V and the non-switching mode starts. In this mode, the SS8028 consumes as little as 20uA typically, saving on battery power. The appropriate inductance value for the boost regulator application may be calculated from the following equation. Select a standard inductor close to this value. Inductor Selection - Boost Regulator
PART LQH3C4R7 LQH3C100 LQH3C220 CD43-4R7 CD43-100 CDRH4D18-4R7 CDRH4D18-100 DO1608-472 DO1608-103 DO1608-223
TABLE 1. RECOMMENDED INDUCTORS
VALUE (uH) 4.7 10 22 4.7 10 4.7 10 4.7 10 22 MAX DCR ? ) 0.26 0.30 0.92 0.11 0.18 0.16 0.20 0.09 0.16 0.37 Coilcraft www.coilcraft.com VENDOR Murata www.murata.com
Sumida www.sumida.com
Choosing an Inductor There are several recommended inductors that work well with the SS8028 in Table 1. Use the equations and recommendations in the next few sections to find the proper inductance value for your design.
L=
VOUT-VIN(MIN)+VD ILIM
x tOFF
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Here, VD = 0.4V (Schottky diode voltage), ILIM = 350mA and tOFF = 500ns. A larger value can be used to slightly increase the available output current, but limit it to about twice the calculated value. When too large an inductor is used, the output voltage ripple will increase without providing much additional output current. In conditions of varying VIN, such as battery power applications, use the minimum VIN value in the above equation. A smaller value can be used to give smaller physical size, but overshoot of the inductor current will occur (see Current Limit Overshoot section).
without any problem, but the total efficiency will suffer. For best performance, the IPEAK is best kept below 500mA. Capacitor Selection Low ESR (Equivalent Series Resistance) capacitors should be used at the output to minimize the output ripple voltage and the peak-to-peak transient voltage. Multilayer ceramic capacitors (MLCC) are the best choice, as they have a very low ESR and are available in very small packages. Their small size makes them a good match with the SS8028's SOT-23 package. If solid tantalum capacitors (like the AVX TPS, Sprague 593D families) or OS-CON capacitors are used, they will occupy more volume than ceramic ones and the higher ESR increases the output ripple voltage. It is important to use a capacitor with a sufficient voltage rating.
Inductor Selection - SEPIC Regulator For a SEPIC regulator using the SS8028, the approximate inductance value can be calculated using the formula below. As for the boost inductor selection, a larger or smaller value can be used.
L=2
VOUT + VD ILIM
x tOFF
A low ESR surface-mount ceramic capacitor also makes a good selection for the input bypass capacitor, which should be placed as close as possible to the SS8028. A 4.7F input capacitor is sufficient for most applications.
Diode Selection
Current Limit Overshoot The SS8028 uses a constant off-time control scheme; the MOSFET is turned off after the 350mA current limit is reached. When the current limit is reached and the MOSFET actually turns off, there is a 100ns delay time. During this time, the inductor current exceeds the current limit by a small amount. The formula below can calculate the peak inductor current.
For most SS8028 applications, the high switching frequency requires high-speed Schottky diodes, such as the Motorola MBR0530 (0.5A, 30V) with their low
IPEAK = ILIM +
VIN(MAX) - VSAT L
x 100ns
forward voltage drop and fast switching speed. Many different manufacturers make equivalent parts, but make sure that the component is rated for at least 0.35A. To achieve high efficiency, the average current rating of the Schottky diodes should be greater than the peak switching current. Choose a reverse breakdown voltage greater than the output voltage.
Lowering Output Ripple Voltage
Here, VSAT = 0.25V (switch saturation voltage). For systems with high input voltages and smaller inductance values, the current overshoot will be most apparent. This overshoot can be useful as it helps increase the amount of available output current. By using a small inductance value, the current limit overshoot can be quite high. Even though it is internally current limited to 350mA, the internal MOSFET of the SS8028 can handle larger currents
The SS8028 supplies energy to the load in bursts by ramping up the inductor current, then delivering that current to the load. Using low ESR capacitors will help
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minimize the output ripple voltage, but proper selection of the inductor and the output capacitor also plays a big role. If a larger inductance value or a smaller capacitance value is used, the output ripple voltage will increase because the capacitor will be slightly overcharged each burst cycle. To reduce the output ripple, increase the output capacitance value, or add a 10pF feed-forward capacitor in the feedback network of the SS8028 (see the circuits in the Typical Applications section). To add this small inexpensive 10pF capacitor will greatly reduce the output voltage ripple.
TYPICAL APPLICATION CIRCUITS
Boost Converter
L1 4.7uH
V
IN
SEPIC Converter
L1 10uH
V
IN
L1:MURATA LQH3C4R7M24 D1:MOTOROLA MBR0520 D1 5V 50mA 390k R1
C3 1uF
1
L1,L2:MURATA LQH3C100K24 D1:MOTOROLA MBR0520 D1 3.3V 60mA
2.5V to 4.2V VCC VCC SW SW
2.5V to 4.2V VCC SW L2 10H 470k R1
G5111
SHDN SHDN C1 4.7F GND FB FB 120k R2
C2 22F C1 4.7F
SHDN
FB 270k R2
C2 22F
GND
L1 10H/0.5A VBAT 2.5V~5.5V C1 4.7F VCC SW
D1
MBR0520 C2 1F D2(Optional) 18V
SS8028
ON/OFF Control SHDN FB
GND
White LED Driver
R2 R3 VBIAS(+3.3V) 308k_1% R4 PWM Dim 660k_1% PWM Dimming Control VH=3.3V VL=0V Freq=160~240Hz 120k_1% R1 30_1%
Dimming Ratio>50:1 Drive 2~4 White LEDs
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PACKAGE DIMENSIONS
SOT-23-5 (unit: mm)
DIMENSIONS IN MILLIMETERS
D C L
SYMBOLS
MIN
A 1.00 0.00 0.70 0.35 0.10 2.70 1.40 --------2.60 0.37 1 A1 A2 b
1
NOM
1.10 ----0.80 0.40 0.15 2.90 1.60 1.90(TYP) 0.95 2.80 -----5
MAX
1.30 0.10 0.90 0.50 0.25 3.10 1.80 --------3.00 ----9
E
H
e1 e
C D E e
A A2 A1
e1 H L ?1
b
1. Package body sizes exclude mold flash protrusions or gate burrs 2. Tolerance 0.1000 mm (4mil) unless otherwise specified 3. Coplanarity: 0.1000mm 4. Dimension L is measured in gage plane
Feed Direction SOT23-5 Package Orientation
Information furnished by Silicon Standard Corporation is believed to be accurate and reliable. However, Silicon Standard Corporation makes no guarantee or warranty, express or implied, as to the reliability, accuracy, timeliness or completeness of such information and assumes no responsibility for its use, or for infringement of any patent or other intellectual property rights of third parties that may result from its use. Silicon Standard reserves the right to make changes as it deems necessary to any products described herein for any reason, including without limitation enhancement in reliability, functionality or design. No license is granted, whether expressly or by implication, in relation to the use of any products described herein or to the use of any information provided herein, under any patent or other intellectual property rights of Silicon Standard Corporation or any third parties.
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