BL8028
1.5A 2MHz 6V Synchronous Buck Converter
DESCRIPTION
FEATURES
The BL8028 is a high-efficiency, DC-to-DC stepdown switching regulators, capable of delivering up
to 1.5A of output current. The device operates from
an input voltage range of 2.6V to 6V and provides
an output voltage from 0.6V to VIN, making the
BL8028 ideal for low voltage power conversions.
Running at a fixed frequency of 2MHz 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. This low
noise output along with its excellent efficiency
achieved by the internal synchronous rectifier,
making BL8028 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.
APPLICATIONS
The BL8028 is available in SOT23-5 and the tiny
DFN2*2-6 packages.
TYPICAL APPLICATION
VIN
2.6V to 6V
VOUT
1.8V
SW
LC2201
BL8028
EN
240k
VIN
5
4
NC 1
NC
FB
GND
FB
GUYW
10uF
GU
YW
10uF
Cellular phones
Digital Cameras
MP3 and MP4 players
Set top boxes
Wireless and DSL Modems
USB supplied Devices in Notebooks
Portable Devices
PIN OUT & MARKING
1uH/2.2uH
VIN
High Efficiency: Up to 97%
Capable of Delivering 1.5A
2MHz Switching Frequency
No External Schottky Diode Needed
Low dropout 100% Duty operation
Internal Compensation and Soft-Start
Current Mode control
0.6V Reference for Low Output voltages
Logic Control Shutdown (IQ2000V
Storage Temperature(Ts)
Lead Temperature & Time
ESD (HBM)
Note: Exceed these limits to damage to the device. Exposure to absolute maximum rating conditions may affect
device reliability.
RECOMMENDED WORK CONDITIONS
Parameter
Value
Input Voltage Range
Operating Junction Temperature(Tj)
6V
-20C –125C
ELECTRICAL CHARACTERISTICS
(Vin=5V, TA=25C, unless otherwise specified.)
Symbol
Parameter
Vin
Input Voltage Range
Vref
Feedback Voltage
IFB
Feedback Leakage current
IQ
Quiescent Current
Conditions
Min
Typ
2.6
Vin=5V
0.588
Active, VFB=0.65, No Switching
Max
Unit
6
V
0.6
0.612
V
0.1
1
uA
80
Shutdown
uA
1
uA
LNR
Line Regulation
Vin=2.6V to 5.5V
0.1
0.2
%/V
LDR
Load Regulation
Iout=0.01 to 1A
0.1
0.2
%/A
FSOC
Switching Frequency
2
2.4
MHz
RDSONP
PMOS Rdson
250
350
mohm
RDSONN
NMOS Rdson
150
250
mohm
VUVLO
Under Voltage Lockout
2.1
2.3
VUVLO_HY
Ilimit
1.6
1.9
UVLO Hysteresis
100
Peak Current Limit
Inoload
1.8
Vin=5V, Vout=3.3V, Iout=0
2.3
2.8
80
A
uA
Iswlk
SW Leakage Current
Ienlk
EN Leakage Current
Vh_en
EN Input High Voltage
Vl_en
EN Input Low Voltage
TSD
Thermal Shutdown Temp
160
°C
TSH
Thermal Shutdown Hysteresis
15
°C
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Vout=6V, VSW=0 or 6V, EN=0V
V
mV
1
uA
1
uA
1.2
V
0.5
2
V
BL8028
PIN DESCRIPTION
NAME
PIN #
EN
GND
SW
VIN
SOT23-5
1
2
3
4
DFN2*2-6
2
5
4
3
FB
5
6
NC
-
1
DESCRIPTION
Enable pin for the IC. Drive the pin to high to enable the part, and low to disable
Ground
Inductor connection. Connect an inductor between SW and the regulator output.
Supply voltage.
Feedback input. Connect an external resistor divider from the output to FB and
GND to set the output to a voltage between 0.6V and Vin
No Connection
ELECTRICAL PERFORMANCE
Tested under TA=25C, unless otherwise specified
Efficiency vs. Output Current
Efficiency vs. Output Current
(Vout=1.8V)
100%
100%
90%
90%
80%
80%
70%
70%
Efficiency
Efficiency
(Vout=1.2V)
60%
50%
40%
50%
40%
30%
30%
Vin=2.5V
Vin=3.3V
Vin=4.0V
Vin=5.5V
20%
10%
0%
0.001
0.01
0.1
Iout (A)
1
10%
10
90%
80%
70%
60%
50%
40%
30%
Vin=4.0V
Vin=5.0V
Vin=5.5V
20%
10%
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0.1
Iout (A)
0.01
0.1
Iout (A)
1
Vin=5V / Vout=1.8V
Ch1—Vin, Ch2—Vout, Ch3—Vsw, Ch4—ISW
(Vout=3.3V)
0.01
0%
0.001
Output Ripple and SW at 1A load
100%
0%
0.001
Vin=2.5V
Vin=3.3V
Vin=4.0V
Vin=5.5V
20%
Efficiency vs. Output Current
Efficiency
60%
1
10
3
10
BL8028
BLOCK DIAGRAM
DETAILED DESCRIPTION
The BL8028 high-efficiency switching regulator is a
small, simple, DC-to-DC step-down converter
capable of delivering up to 1.5A of output current.
The device operates in pulse-width modulation
(PWM) at 2MHz from a 2.6V to 6V input voltage
and provides an output voltage from 0.6V to VIN,
making the BL8028 ideal for on-board postregulation 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
BL8028 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
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4
error signal. During the off cycle, the internal highside 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 highside MOSFET of 2.3A (typ). When the current
flowing out of SW exceeds this limit, the high-side
MOSFET turns off and the synchronous rectifier
turns on. BL8028 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
100mV, limiting the current to 2.3A (typ) and
reducing power dissipation. Normal operation
resumes upon removal of the short-circuit
condition.
BL8028
Soft-start
RTOP = RBOTTOM[(VOUT / 0.6) - 1]
BL8028 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 soft-start circuitry
slowly ramps up current available at SW.
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)]
UVLO and Thermal Shutdown
If VIN drops below 2.1V, the UVLO circuit inhibits
switching. Once VIN rises above 2.2V, 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= +160°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.
If the capacitor has significant ESR, the output
ripple component due to capacitor ESR is as follows:
VRIPPLE(ESR) = IL(PEAK) x ESR
Design Procedure
Setting Output Voltages
Output voltages are set by external resistors. The
FB_ threshold is 0.6V.
LAYOUT GUIDE
The blue line is placed
on the back side.
Cout as close as
possible to Vout
Cout
Vout
L
GND
FB&GND connect to
R1 directly as short
as possible
Keep the path below
shortly and wide for
low resistance
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FB
VIN
Make GND loop
Resistance as
small as possible
SW
SW
Jumper
Off
EN
On
GND
Keep the path below
short and wide for low
resistance
VIN
Cin
5
Cin as close as
possible to VIN
R1
R2
BL8028
PACKAGE OUTLINE
Package
SOT23-5
Devices per reel
3000
Unit
mm
Devices per reel
3000
Unit
mm
Package specification:
Package
DFN2x2-6
Package specification:
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6