English

BL9315
5V 3A 1.4MHz Synchronous Buck Converter
BL9315
5V 3A 1.4MHz Synchronous Buck Converter
GENERATION DESCRIPTION
The BL9315 is a high-efficiency, DC-to-DC step-down switching regulators, capable of delivering up to 3A of output
current. The device operates from an input voltage range of 2.5V to 5.5V and provides an output voltage greater than 0.6V,
making the BL9315 ideal for low voltage power conversions.
Running at a frequency of 1.4MHz allows the use of small external components, such as ceramic input and output caps,
as well as small inductors, while still providing low output ripples. The light-load mode enhances the light loading
efficiency. The low noise output along with its excellent efficiency achieved by the internal synchronous rectifier, making
BL9315 an ideal green replacement for large power consuming linear regulators.
Internal soft-start control circuitry reduces inrush current. Short-circuit and thermal-overload protection improves design
reliability.
The BL9315 is available in ESOP8 package.
FEATURES

High Efficiency: Up to 97%

Capable of Delivering 3A

Input Voltage: 2.5~5.5V

1.4MHz Switching Frequency

No External Schottky Diode Needed

Light-load Mode

Internal Compensation and Soft-Start

Current Mode control

0.6V Reference for Low Output voltages

Logic Control Shutdown (IQ<1uA)

Thermal shutdown and UVLO

Available in ESOP8
APPLICATIONS

Digital Cameras

MP3 and MP4 players

Set top boxes

Wireless and DSL Modems

USB supplied Devices in Notebooks

Portable Devices
TYPICAL APPLICATION CIRCUIT
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BL9315
5V 3A 1.4MHz Synchronous Buck Converter
PIN ASSIGNMENT
ORDER INFORMATION
PART NO
PACAKGE
TEMPERATURE
TAPE & REEL
BL9315
ESOP8
-40 ~ +85℃
2500/REEL
PIN DESCRIPTION
PIN NO
SYMBOL
1
NC
2
VIN
3
SW
4
GND
5
FB
6
NC
7
EN
8
NC
(Exposed PAD)
DESCRIPTTION
Not Connected
Analog Supply Input
Power Switch Output
Ground
Feedback input pin
Not Connected
Enable pin
Not Connected
Ground
ABSOLUTE MAXIMUM RATINGS (Note 1)
Parameter
Max Input Voltage
Max Operating Junction Temperature(Tj)
Maximum Power Dissipation, ESOP8
Storage Temperature(Ts)
Lead Temperature & Time
Value
6.5V
125C
1.3W
-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
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ITEMS
VIN Supply Voltage
Operating Temperature
VALUE
2.5 to 5.5
-40 to +85
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UNIT
V
℃
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BL9315
5V 3A 1.4MHz Synchronous Buck Converter
ELECTRICAL CHARACTERISTICS (Note 2, 3)
(VDD=5V, TA=25C)
Symbol
VIN
VFB
IFB
IQ
ISD
FSW
RONP
RONN
ILIMIT
ISW
IEN
VENH
VENL
TSD
HYSTSD
Parameter
Conditions
Input Voltage Range
Feedback Voltage
Feedback Leakage current
Quiescent Current
Shutdown Current
Switching Frequency
PMOSFET RDSON
NMOSFET RDSON
Peak Current Limit
SW Leakage Current
Min
Typ
2.5
0.585
Active, VFB=0.65V
Shutdown
0.6
0.1
50
Max
Unit
5.5
V
0.615
0.4
V
uA
uA
uA
MHz
mΩ
mΩ
A
1
1.4
120
80
3.5
VIN=5.5V, VSW=0 or
5.5V, VEN=0V
EN Leakage Current
EN Input High Voltage
EN Input Low Voltage
Thermal Shutdown
Thermal Shutdown
Hysteresis
10
uA
1
uA
V
V
1.5
0.4
150
C
15
C
SIMPLIFIED BLOCK DIAGRAM
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BL9315
5V 3A 1.4MHz Synchronous Buck Converter
OPERATION DESCRIPTION
The BL9315 high-efficiency switching regulator is a small, simple, DC-to-DC step-down converter capable of
delivering up to 3A of output current. The device operates in pulse-width modulation (PWM) at 1.4MHz from
a 2.5V to 5.5V input voltage and provides an output voltage from 0.6V on, making the BL9315 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
The BL9315 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 3.5A. When the current flowing out of SW
exceeds this limit, the high-side MOSFET turns off and the synchronous rectifier turns on. BL9315 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 3.5A and reducing
power dissipation. Normal operation resumes upon removal of the short-circuit condition.
Soft-start
The BL9315 has an 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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BL9315
5V 3A 1.4MHz Synchronous Buck Converter
TYPICAL OPERATING CHARACTERISTICS
Tested under TA=25C, unless otherwise specified
1.
Efficiency
2.
Load Regulation
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BL9315
5V 3A 1.4MHz Synchronous Buck Converter
3.
Ripple for light-load and normal load
4.
SW and VOUT for light-load and normal load
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BL9315
5V 3A 1.4MHz Synchronous Buck Converter
5.
Transient for 0 to 3A and 0.5A to 3A
6.
Soft Start for VOUT and SW
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BL9315
5V 3A 1.4MHz Synchronous Buck Converter
7.
Short Circuit Protection
8.
Over-Thermal Protection and Recovery
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BL9315
5V 3A 1.4MHz 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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BL9315
5V 3A 1.4MHz Synchronous Buck Converter
PACKAGE OUTLINE
ESOP8
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