English

BL9309
5.5V 2.0A 1.3MHz Synchronous Buck Converter
GENERATION DESCRIPTION
FEATURES
The BL9309 is a high-efficiency, DC-to-DC step-down
switching regulators, capable of delivering up to 2A of


High Efficiency: Up to 97%
Capable of Delivering 2A
output current. The device operates from an input voltage

1.3MHz Switching Frequency
range of 2.5V to 5.5V and provides an output voltage

No External Schottky Diode Needed
from 0.6V to VIN, making the BL9309 ideal for low

Light-load Mode
voltage power conversions. Running at a fixed frequency

Internal Compensation and Soft-Start
of 1.3MHz allows the use of small external components,

Current Mode control
such as ceramic input and output caps, as well as small

0.6V Reference for Low Output voltages
inductors, while still providing low output ripples. This

Logic Control Shutdown (IQ<1uA)
low noise output along with its excellent efficiency

Thermal shutdown and UVLO

Available in SOT23-6
achieved by the internal synchronous rectifier, making
BL9309 an ideal green replacement for large power
APPLICATIONS
consuming linear regulators. Internal soft-start control
circuitry reduces inrush current. Short-circuit and
thermal-overload protection improves design reliability.
The BL9309 is available in a SOT23-6 Package.
TYPICAL APPLICATION CIRCUIT


Digital Cameras
MP3 and MP4 players

Set top boxes

Wireless and DSL Modems

USB supplied Devices in Notebooks

Portable Devices
PIN ASSIGNMENT
ORDER INFORMATION
PART NO
BL9309
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PACKAGE
TEMPERATURE
TAPE & REEL
SOT23-6
-40 ~ +85℃
3000/REEL
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BL9309
5.5V 2.0A 1.3MHz Synchronous Buck Converter
PIN DESCRIPTION
PIN NO
SYMBOL
1
2
3
4
5
6
EN
GND
SW
IN
NC
FB
DESCRIPTTION
Enable pin
Ground
Power Switch Output
Power Supply Input
Not Connected
Feedback input pin
ABSOLUTE MAXIMUM RATINGS (Note 1)
Parameter
Max Input Voltage
Max Operating Junction Temperature(Tj)
Ambient Temperature(Ta)
Maximum Power Dissipation
SOT23-5
Storage Temperature(Ts)
Lead Temperature & Time
Value
6.5V
125C
-40C – 85C
400mW
-40C - 150C
260C, 10S
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Recommended
Operating Range indicates conditions for which the device is functional, but do not guarantee specific performance
limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which
guarantee specific performance limits. This assumes that the device is within the Operating Range. Specifications are
not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device
performance.
RECOMMANDED OPERATING RANGE
SYMBOL
VIN
TOPT
ITEMS
VIN Supply Voltage
Operating Temperature
VALUE
2.5 to 5.5
-40 to +85
UNIT
V
℃
ELECTRICAL CHARACTERISTICS (Note 2, 3)(VDD=5V, TA=25C)
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BL9309
5.5V 2.0A 1.3MHz Synchronous Buck Converter
SIMPLIFIED BLOCK DIAGRAM
OPERATION DESCRIPTION
The BL9309 high-efficiency switching regulator is a small, simple, DC-to-DC step-down converter capable of
delivering up to 2A of output current. The device operates in pulse-width modulation (PWM) at 1.3MHz
from a 2.5V to 5.5V input voltage and provides an output voltage from 0.6V on, making the BL9309 ideal
for on-board post-regulation applications. An internal synchronous rectifier improves efficiency and
eliminates the typical Schottky free-wheeling diode. Using the on resistance of the internal high-side
MOSFET to sense switching currents eliminates current-sense resistors, further improving efficiency and
cost.
Loop Operation
BL9309 uses a PWM current-mode control scheme. An open-loop comparator compares the integrated
voltage-feedback signal against the sum of the amplified current-sense signal and the slope compensation
ramp. At each rising edge of the internal clock, the internal high-side MOSFET turns on until the PWM
comparator terminates the on cycle. During this on-time, current ramps up through the inductor, sourcing
current to the output and storing energy in the inductor. The current mode feedback system regulates the
peak inductor current as a function of the output voltage error signal. During the off cycle, the internal
high-side P-channel MOSFET turns off, and the internal low-side N-channel MOSFET turns on. The inductor
releases the stored energy as its current ramps down while still providing current to the output.
Current Sense
An internal current-sense amplifier senses the current through the high-side MOSFET during on time and
produces a proportional current signal, which is used to sum with the slope compensation signal. The
summed signal then is compared with the error amplifier output by the PWM comparator to terminate the
on cycle.
Current Limit
There is a cycle-by-cycle current limit on the high-side MOSFET of 2.5A. When the current flowing out of SW
exceeds this limit, the high-side MOSFET turns off and the synchronous rectifier turns on. BL9309 utilizes a
frequency fold-back mode to prevent overheating during short-circuit output conditions. The device enters
frequency fold-back mode when the FB voltage drops below 200mV, limiting the current to 2.5A and
reducing power dissipation. Normal operation resumes upon removal of the short-circuit condition.
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BL9309
5.5V 2.0A 1.3MHz Synchronous Buck Converter
Soft-start
BL9309 has a internal soft-start circuitry to reduce supply inrush current during startup conditions. When
the device exits under-voltage lockout (UVLO), shutdown mode, or restarts following a thermal-overload
event, the l soft-start circuitry slowly ramps up current available at SW.
UVLO and Thermal Shutdown
If IN drops below 2.5V, the UVLO circuit inhibits switching. Once IN rises above 2.5V, the UVLO clears, and
the soft-start sequence activates. Thermal-overload protection limits total power dissipation in the device.
When the junction temperature exceeds TJ= +150°C, a thermal sensor forces the device into shutdown,
allowing the die to cool. The thermal sensor turns the device on again after the junction temperature cools
by 15°C, resulting in a pulsed output during continuous overload conditions. Following a thermal-shutdown
condition, the soft-start sequence begins.
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BL9309
5.5V 2.0A 1.3MHz Synchronous Buck Converter
TYPICAL OPERATING CHARACTERISTICS
Tested under TA=25C, unless otherwise specified
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BL9309
5.5V 2.0A 1.3MHz Synchronous Buck Converter
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BL9309
5.5V 2.0A 1.3MHz Synchronous Buck Converter
APPLICATION INFORMATION
Setting Output Voltages
Output voltages are set by external resistors. The FB_ threshold is 0.6V.
RTOP = RBOT [(VOUT / 0.6) - 1]
Input Capacitor Selection
The input capacitor in a DC-to-DC converter reduces current peaks drawn from the battery or other input
power source and reduces switching noise in the controller. The impedance of the input capacitor at the
switching frequency should be less than that of the input source so high-frequency switching currents do
not pass through the input source. The output capacitor keeps output ripple small and ensures control-loop
stability. The output capacitor must also have low impedance at the switching frequency. Ceramic, polymer,
and tantalum capacitors are suitable, with ceramic exhibiting the lowest ESR and high-frequency impedance.
Output ripple with a ceramic output capacitor is approximately as follows:
VRIPPLE = IL(PEAK)[1 / (2π x fOSC x COUT)]
If the capacitor has significant ESR, the output ripple component due to capacitor ESR is as follows:
VRIPPLE(ESR) = IL(PEAK) x ESR
Output Capacitor and Inductor Selection
Follow the below table for Inductor and Output cap selection:
VOUT
COUT
L
1.2V
33F
1.5H
1.5V
33F
1.5H
1.8V
22F
2.2H
2.5V
22F
3.3H
3.3V
10F
4.7H
If much smaller values are used, inductor current rises, and a larger output capacitance may be required to
suppress output ripple. Larger values than LIDEAL can be used to obtain higher output current, but typically
with larger inductor size.
Layout Guideline
Layout is critical to achieve clean and stable operation. The switching power stage requires particular
attention. Follow these guidelines for good PC board layout:
1) Place decoupling capacitors as close to the IC as possible
2) Connect input and output capacitors to the same power ground node with a star ground configuration
then to IC ground.
3) Keep the high-current paths as short and wide as possible. Keep the path of switching current (C1 to IN
and C1 to GND) short. Avoid vias in the switching paths.
4) If possible, connect IN, SW, and GND separately to a large copper area to help cool the IC to further
improve efficiency and long-term reliability.
5) Ensure all feedback connections are short and direct. Place the feedback resistors as close to the IC as
possible.
6) Route high-speed switching nodes away from sensitive analog area.
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BL9309
5.5V 2.0A 1.3MHz Synchronous Buck Converter
PACKAGE OUTLINE
L
SOT23-6
SYMBOL
A
A1
A2
b
c
D
E
E1
e
e1
L
L1
θ
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MILLIMETERS
INCHES
MIN
MAX
1.050
1.250
0.000
0.100
1.050
1.150
0.300
0.400
0.100
0.200
2.820
3.020
1.500
1.700
2.650
2.950
0.950TYP
1.800
2.000
0.700REF
0.300
0.600
0°
8°
MIN
MAX
0.041
0.049
0.000
0.004
0.041
0.045
0.012
0.016
0.004
0.008
0.111
0.119
0.059
0.067
0.104
0.116
0.037TYP
0.071
0.079
0.028REF
0.012
0.024
0°
8°
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