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Rev PrB, 20-Feb-08 Preliminary Product InformationAll Information Subject to Change
ACT6308
Low Input High Efficiency Synchronous Step-Up DC/DC Converter FEATURES
* * * * * *
1V Typical Startup Voltage Up to 89% Efficiency Fully Integrated Power Stage Fixed 3.3V/5V or Adjustable Output Voltage NanoStandbyTM Shutdown Mode Tiny SOT23-5 Package - RoHS Compliant Package
GENERAL DESCRIPTION
The ACT6308 is a high efficiency synchronous step-up DC/DC converter that consumes just 17A of quiescent supply current using only three external components. This device achieves a typical startup voltage of just 1V, making it ideal for applications operating from 1 or 2 alkaline cells. This device incorporates an internal synchronous rectifier, and achieves excellent peak efficiency of up to 89% and features a proprietary control scheme that ensures high efficiency over a wide load current range. The ACT6308 features pin-selectable output voltages of 3.3V or 5V, or it can also be set externally to any voltage between 2V and 5V. The ACT6308 is available in a tiny SOT23-5 package.
APPLICATIONS
* * * * * *
Hand-Held Devices One to Three Cell Battery Operated Devices PDAs Cellular Phones Digital Cameras GPS
TYPICAL APPLICATION CIRCUIT
Efficiency vs. Output Current
VIN
L 2.2H LX OUT
VOUT 3.3V
1.00
ACT6308-001
EN C1 2.2F
G
FB C2 4.7F
Efficiency (%)
ENABLE
ACT6308
0.90
VIN = 2.4V
0.80
0.70 VIN = 1.8V 0.60 0.50 VIN = 1.5V VOUT = 3.3V FB = GND 10 100 1000
Pb-free
0.1
1.0
Output Current (mA)
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ACT6308
Rev PrB, 20-Feb-08
ORDERING INFORMATION
PART NUMBER
ACT6308UC-T
TEMPERATURE RANGE
-40C to 85C
PACKAGE PINS
SOT23-5 5
PACKING METHOD
TAPE & REEL
TOP MARK
HBCB
All Active-Semi components are RoHS Compliant and with Pb-free plating unless specified differently. The term "Pb-free" means semiconductor products that are in compliance with current RoHS (Restriction of Hazardous Substances) standards.
PIN CONFIGURATION
FB 1 5 OUT
G
2
ACT6308
4 LX
EN
3
SOT23-5
PIN DESCRIPTION
PIN NUMBER PIN NAME
1 2 3 4 5 FB G EN LX OUT
PIN DESCRIPTION
Output Voltage Selection and Feedback Input. Connect this pin to G for VOUT = 5V, to OUT for VOUT = 3.3V. Connect FB to a resistor divider to set the output voltage between 2V and 5V. See the Output Voltage Selection section for more information. Ground. Shutdown Input. Drive EN to OUT or to a logic high for normal operation, drive EN to G or to a logic low to disable the regulator. Inductor Connection. Output. ACT6308 regulates voltage at this pin. OUT also provides power to the IC.
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ACT6308
Rev PrB, 20-Feb-08
ABSOLUTE MAXIMUM RATINGS
PARAMETER
OUT, EN to G FB, LX to G Continuous LX Current Maximum Power Dissipation (derate 5mV/C above TA = 50C) Junction to Ambient Thermal Resistance (JA) Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, 10 sec)
VALUE
-0.3 to 6 -0.3 to VOUT + 0.3 Internally Limited 0.53 190 -40 to 150 -55 to 150 300
UNIT
V V A W C/W C C C
: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN = 1.5V, VOUT = 3.3V, TA = 25C, unless otherwise specified.)
PARAMETER
Minimum Operating Input Voltage Maximum Operating Input Voltage Startup Voltage Output Voltage Output Voltage Range Quiescent Current at OUT Shutdown Supply Current Startup to Normal Transition Threshold FB Feedback Voltage FB Input Current Power Switch Current Limit Power Switch On Resistance Synchronous Rectifier On Resistance LX Leakage Current Maximum Switch On-Time Minimum Switch Off-Time EN Logic Low Threshold EN Logic High Threshold EN Input Current
SYMBOL
VIN VIN VIN VOUT
TEST CONDITIONS
MIN
TYP
0.6
MAX
5
UNIT
V V V V V A A V
ILOAD = 1mA FB = OUT; 60mVPP Ripple FB = G; 40mVPP Ripple External Feedback Divider 3.2 4.85 2
1 3.3 5
1.18 3.4 5.15 5
IQ ISD
VFB = 1.3V EN = G
17 0.1 1.85
34 1
VFB
VOUT = 2V to 5V FB = 1.3V
1.15
1.180 50
1.21
V nA
ILIM RONN RONP ILX = 100mA ILX = -100mA EN = G, VLX = 0 or 3.3V tONMAX tOFFMIN VIL VIH
0.35
0.4 0.19 0.21 0.1
0.6 0.4 0.4 1 1.8 0.36 0.4
A A s s V V
1.2 0.24
1.5 0.3
0.6 1
A
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ACT6308
Rev PrB, 20-Feb-08
TYPICAL PERFORMANCE CHARACTERISTICS
(Typical Application Circuit, L = 2.2H, C1 = 2.2F ceramic, C2 = 4.7F ceramic, unless otherwise specified.)
Efficiency vs. Output Current
1.00 100 ACT6308-001
Efficiency vs. Output Current
ACT6308-002
0.90
90
Efficiency (%)
VIN = 2.4V
0.80
VIN = 3.7V
Efficiency (%)
80
0.70 VIN = 1.2V VIN = 2.4V VOUT = 5V FB = GND 100 1000
70 VIN = 1.8V VIN = 1.5V VOUT = 3.3V FB = GND 10 100 1000
0.60 0.50
60 50 0.1 1.0
0.1
1.0
10
Output Current (mA)
Output Current (mA)
Startup Voltage vs. Constant Current Load
2.00 1.75 1.50 1.25 1.00 0.75 0.50 0 20 40 60 80 VOUT = 3.3V 100 200 ACT6308-003
Startup Voltage vs. Constant Resistance Load
2.00 1.75 1.50 1.25 1.00 0.75 0.50 0 20 40 60 80 VOUT = 3.3V 100 200 ACT6308-004
Startup Voltage (V)
Constant Current Load (mA)
Startup Voltage (V)
Current Load at 3.3V (mA)
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ACT6308
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TYPICAL PERFORMANCE CHARACTERISTICS CONT'D
(Typical Application Circuit, L = 2.2H, C1 = 2.2F ceramic, C2 = 4.7F ceramic, unless otherwise specified.)
Startup Voltage vs. Temperature
1.5 ACT6308-005 6.5
Maximum On-Time vs. Temperature
ACT6308-006
1.0
Maximum On-Time (S)
Startup Voltage (V)
5.5
0.5 -40 -20 0 20 40 60 80 100 120
4.5 -40 -20 0 20 40 60 80 100 120
Temperature (C)
Temperature (C)
Minimum Off-Time vs. Temperature Quiescent Supply Current (A)
1.5 25 20 ACT6308-007
Quiescent Supply Current vs. Temperature
ACT6308-008
Minimum Off-Time (S)
1.4
1.3
15
1.2
10
1.1 1.0 -40 -20 0 20 40 60 80 100 120
5 0 -40 -20 0 20 40 60 80 100 120
Temperature (C)
Temperature (C)
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ACT6308
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TYPICAL PERFORMANCE CHARACTERISTICS CONT'D
(Typical Application Circuit, L = 2.2H, C1 = 2.2F ceramic, C2 = 4.7F ceramic, unless otherwise specified.)
Light Load Operation for Low ESR COUT
ACT6308-009
VOUT = 3.3V VOUT = 3.3V VIN = 1.8V ILOAD = 5mA
Light Load Operation for Low ESR COUT
ACT6308-010
VOUT = 5V VIN = 3.6V ILOAD = 5mA
CH1
CH1
CH2
CH2
CH1: VOUT, 20.0mV/div CH2: ILX, 200mA/div TIME: 10.0s/div
CH1: VOUT, 20.0mV/div CH2: ILX, 200mA/div TIME: 20.0s/div
Medium Load Operation for Low ESR COUT
ACT6308-011
VOUT = 3.3V VIN = 1.8V ILOAD = 50mA
Medium Load Operation for Low ESR COUT
ACT6308-012
VOUT = 5V VIN = 3.6V ILOAD = 50mA
CH1
CH1
CH2
CH2
CH1: VOUT, 20.0mV/div CH2: ILX, 200mA/div TIME: 2.00s/div
CH1: VOUT, 20.0mV/div CH2: ILX, 200mA/div TIME: 2.00s/div
Heavy Load Operation for Low ESR COUT
ACT6308-013
VOUT = 3.3V VIN = 1.8V ILOAD = 100mA
Heavy Load Operation for Low ESR COUT
ACT6308-014
VOUT = 5V VIN = 3.6V ILOAD = 110mA
CH1
CH1
CH2
CH2
CH1: VOUT, 20.0mV/div CH2: ILX, 200mA/div TIME: 2.00s/div
CH1: VOUT, 20.0mV/div CH2: ILX, 200mA/div TIME: 2.00s/div
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ACT6308
Rev PrB, 20-Feb-08
FUNCTIONAL BLOCK DIAGRAM
OUT LOW INPUT START UP
EN
REFERENCE
VREF
0.3s ONE-SHOT
SET LATCH Q RESET
1.5s ONE-SHOT
DRIVER
LX
VREF FEEDBACK SELECT
FB
CURRENT LIMIT COMPARATOR
FUNCTIONAL DESCRIPTION
As seen in the Functional Block Diagram, the ACT6308 comprises a reference, low input startup circuitry, feedback select, error comparator, control logic and timers, internal power MOSFETs and current comparators.
Light Load Operation
Under light load conditions, the IC automatically enters a power-saving mode by extending the OFF time. This reduces switching losses and allows the ACT6308 to maintain high efficiency across a very wide load range.
Main Control Loop
The ACT6308 control architecture utilizes a series of one-shot and current sense circuits to regulate the output voltage with a very low quiescent supply current of just 17A. An ON cycle begins when FB falls below the ACT6308's internal reference voltage. During an ON cycle, the N-channel power switch is turned on to connect the LX node to ground, transferring energy from input supply to the inductor. The ON cycle persists or the 0.4A current limit is reached. When either of these conditions occurs, the N-channel power switch turns off and the OFF cycle begins. During the OFF cycle, the energy stored in the inductor is released into the output capacitor and load through the synchronous rectifier. Once the 0.3s minimum OFF time expires, another ON cycle begins when the FB voltage drops below the reference voltage.
Low Voltage Startup
The ACT6308 uses proprietary start-up circuitry that allows it to achieve very low voltage startup down to 1V. The ACT6308 remains in low voltage startup mode until VOUT exceeds 1.85V. The ACT6308 cannot support its full rated load current when operating in low-voltage startup mode. Care should be taken to minimize load current during startup.
Shutdown
In shutdown mode, all internal circuits including the power switch and the synchronous rectifier are disabled, reducing quiescent supply current to less than 1A. Note that in shutdown mode, a DC path from the input supply to the output still exists due to the body diode of the synchronous rectifier.
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+
+
-
+
ERROR COMPARATOR G
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ACT6308
Rev PrB, 20-Feb-08
APPLICATIONS INFORMATION
Output Voltage Selection
The ACT6308 provides fixed output voltage options of 3.3V or 5V, or the output voltage may be adjusted over a 2V to 5V range by connecting an external resistive voltage divider. When Output Voltage is set by external resistive voltage divider, add a 47pF to 150pFcapacitor as feed forward capacitor (CFF) as shown in Figure 1. Table 1: Output Voltage Programming
FB = OUT FB = G FB connect to resistive divider VOUT = 3.3V VOUT = 5V VOUT = 1.18V (1 + RFB1/RFB2)
output current. Choose inductors with low series resistance to obtain the highest efficiency.
Board Layout
To reduce noise and increase efficiency, high current traces should be wide and direct, and an extended ground plane should be used. Switching current paths should be laid out as tightly as possible, with the inductor and input and output capacitors located close to the IC in order to reduce electromagnetic radiation. If an external resistor divider is used, place the resistors very close to the FB and G pins, and keep them away from the high switching current paths.
Figure 1: Output Voltage Setting
VOUT
OUT
CFF RFB1
ACT6308
FB
RFB2
Output Capacitor Selection
A minimum value of output capacitance is required to maintain loop stability and normal operation of the IC. The output capacitor value should be in the range of 2.2F to 100F. To obtain small output ripple, use a large capacitor with low ESR. Ceramic capacitors should be used for highest performance. If a tantalum capacitor is used, choose only low ESR types and a smaller low ESR capacitor of about 1F can be connected in parallel to filter high frequency noise.
Inductor Selection
For most applications, the inductor value should be in the range of 1.5H to 22H. Smaller inductors provide faster load transient response and have a smaller physical size, but they also result in higher ripple current and reduce the maximum available
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ACT6308
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PACKAGE OUTLINE
SOT23-5 PACKAGE OUTLINE AND DIMENSIONS
D b L1 0.2
SYMBOL
A A1
DIMENSION IN MILLIMETERS MIN
1.050 0.000 1.050 0.300 0.100 2.820 1.500 2.650
DIMENSION IN INCHES MIN
0.041 0.000 0.041 0.012 0.004 0.111 0.059 0.104
MAX
1.250 0.100 1.150 0.400 0.200 3.020 1.700 2.950
MAX
0.049 0.004 0.045 0.016 0.008 0.119 0.067 0.116
E1
E
A2 b c L
e e1
c
D E E1 e
0.950 TYP 1.800 2.000
0.037 TYP 0.071 0.079
A1
A2
A
e1 L L1
0.700 REF 0.300 0 0.600 8
0.028 REF 0.012 0 0.024 8
Active-Semi, Inc. reserves the right to modify the circuitry or specifications without notice. Users should evaluate each product to make sure that it is suitable for their applications. Active-Semi products are not intended or authorized for use as critical components in life-support devices or systems. Active-Semi, Inc. does not assume any liability arising out of the use of any product or circuit described in this datasheet, nor does it convey any patent license. Active-Semi and its logo are trademarks of Active-Semi, Inc. For more information on this and other products, contact sales@active-semi.com or visit http://www.active-semi.com. For other inquiries, please send to: 1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044, USA
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