BL8542B - 上海贝岭股份有限公司

BL8542B
REV1.2, DEC 2010
0.85V startup, 1MHz, 300mA Iout, Synchronous Boost Converter
DESCRIPTION
FEATURES
The BL8542B is a step-up converter that provides a
boosted output voltage from a low voltage source.
Because of its proprietary design, it starts up at a
very low input voltage down to 850mV, making it
an ideal choice for single cell alkaline/NiMH battery
operations.
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A switching frequency of 1MHz minimizes solution
footprint by allowing the use of tiny, low profile
inductors and ceramic capacitors. The current mode
PWM design is internally compensated, reducing
external parts count.
BL8542B is housed in a tiny SOT23-5 and SOT89-3
Package.
TYPICAL APPLICATION CIRCUIT
BL8542B
BL8542B
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Up to 95% Efficiency
Output voltage accuracy 3%
1MHz Switching Frequency allows small inductor
and output cap
Input boost-strapping allows using small or no
input cap
Low Vin Start-up Voltage down to 850mV Ideal
for Single Alkaline Cell operations
Maximum Output Current up to 300mA
Low Noise PWM control
Internally Compensated Current Mode Control
Internal Synchronous Rectifier
Logic Control Shutdown (IQ<1uA)
APPLICATIONS
••
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••
One to Three Cell Battery Operated Devices
Medical Instruments
Bluetooth Headsets
Flash-Based MP3 Players
Noise Canceling Headphones
PIN CONFIGURATION
3
BL8542B
BL8542B
2 OUT
1
SOT23-5
NOTE: Input capacitor (Cin=0.47uF) and Output capacitor
(Cout≥4.7uF) are recommended in all application circuit.
SW
G
SOT89-3
ORDERING INFORMATION
Product
Product Code
Package
Devices per Reel
Top Marking
BL8542B-ADJ
BL8542BCB5TR
SOT23-5
3000
AAXZ
BL8542B-3.3V
BL8542BCB5TR33
SOT23-5
3000
AAWZ
BL8542B-5.0V
BL8542BCB5TR50
SOT23-5
3000
AAVZ
BL8542B-3.3V
BL8542BCC3TR33
SOT89-3
1000
AAWZ
XXXX
BL8542B-5.0V
BL8542BCC3TR50
SOT89-3
1000
AAVZ
XXXX
XXXX:The last 4 characters of the LOT NO.
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BL8542B
BLOCK DIAGRAM
OUT
EN
Low Input startup
osc
Reference
+
GM
FB
-
+
Comparator
Logic
SW
Driver
-
+
G
DETAIL DESCRIPTION
APPLICATION INFORMATION
BL8542B is a low input voltage start up,
current mode dc-dc step up converter.
It’s operation can be best understood
by referring to the block diagram. Upon
star ting up, the low voltage star tup
circuitry drives SW with on-off cycles,
transferring energy from input to OUT
by storing energy in the inductor during
on-time and releasing it to the output
during off-time. When OUT reaches
2V, the startup circuit turns off and the
main controller takes over. The main
control loop consists of a reference, a
GM error amplifier, a PWM controller, a
current sense amplifier, an oscillator, a
PWM logic control, and it is power stage
including its driver. The main control
loop is a classic current mode control
loop. The GM stage integrates the error
between FB and REF, and its output is
used to compare with a triangular wave
which the summing result of the current
sense amplifier output and a slope
compensation voltage. The output of the
comparator is used to drive the power
stage to reach regulation.
Output Voltage selection
The output voltages can be set by connecting FB to OUT, to G or to
the midpoint of a resistor divider connected to OUT. See below table
for details.
FB=G
VOUT =5.0V
FB=OUT
VOUT =3.3V
FB to resistor divider
VOUT=0.6V(1+R1/R2)
Inductor selection
With switching frequency up to 1MHz, small surface mount inductors
can be used with values from 2.2uH to 4.7uH. For a given chosen
inductor value and application conditions make sure the peak inductor
current does not exceed the maximum current rating of the selected
vendor's inductor.
Input and output capacitor selection
The BL8542B's bootstrap architecture allows the use of very small
input capacitor. For applications that only need to drive small output
load current, the input capacitor is optional, because once output is
started up, the IC's is powered by OUT, a quiet power supply.
The output capacitor is used to stabilize the loop and provide ac
current to the load. A low ESR ceramic cap with values from 2.2uF
to 22uF can be used. Smaller value capacitors are generally cheaper
with small footprints, while larger capacitor provides lower ripples
and better transient load responses. Also, when extreme low startup
voltage is needed, larger output capacitors are needed for the part to
startup under heavy load condition.
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BL8542B
ABSOLUTE MAXIMUM RATING
Parameters
Value
SW Voltage
-0.3 ~ 6 V
EN, FB, OUT Voltage
-0.3 ~ 6 V
Juntion to Ambient Thermal Resistance
190 oC/W
Maximum Power Dissipation
0.45 W
Operating Temperature Range
-40 ~ 150 oC
Storage Temperature
-55 ~ 150 oC
IR Reflow Lead Temperature and Time
260oC , 10s
Note:
Exceed these limits to damage to the device.
Exposure to absolute maximum rating conditions may affect device reliability.
ELECTRICAL CHARACTERISTICS
o
Test condition: Vin=1.8V, Vout=3.3V, TA=25 C, unless otherwise specified.
Parameters
Condition
Min.
Typ.
Minimum Input Voltage
0.7
Startup Voltage
0.85
Dropout Voltage, Vout≥2.8V
FB Feedback Voltage
FB=OUT
FB=G
Vout=2.5 to 5V
Max.
Unit
V
1.1
V
3.3
V
5
V
0.6
V
FB Input Current
50
nA
5
V
Output Voltage Range
External divider
Quiescent Current at OUT
Vfb=0.7V
25
Shutdown Supply Current at OUT
EN=G
0.1
NMOS Switch On Resistance
Isw=100mA
0.3
ohm
PMOS Switch On Resistance
Isw=100mA
0.7
ohm
NMOS Switch Current Limit
SW Leakage Current
2.5
1
1
Vout=5.5V, Vsw=0 or 5.5V,
EN=G
EN Input Current
EN Input Voltage for “Low”
EN Input Voltage for “High”
uA
0.6
uA
A
1
uA
1
uA
0.3
V
V
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BL8542B
TYPICAL PERFORMANCE CHARACTERISTICS
o
Typical values are tested at TA=25 C, unless otherwise specified.
Efficiency vs. Output Current
Efficiency vs. Output Current
(Vout=3.3V; Ta=25℃)
(Vout=5V; Ta=25℃)
100
100
V IN=2.4V
90
V IN=1.2V
80
80
Efficiency(%)
70
Efficiency(%)
VIN=2.4V
90
VIN=1.8V
60
50
VIN=1.8V
70
V IN=1.2V
60
50
40
40
30
30
20
20
1
10
100
1
1000
10
Output Voltage vs. Output Current
( Vout=3.3V;Ta=25℃)
100
1000
Output Current(mA)
Output Current(mA)
Minimum Start-Up Voltage vs. Output Current
(Vout=3.3V,Ta=25℃)
3.25
2
1.8
Start-up Voltage(V)
Output Voltage(V)
3.2
VIN=1.2V
3.15
VIN=1.8V
VIN=2.4V
3.1
3.05
1.6
1.4
1.2
1
0.8
3
0
50
100
150
200
250
300
350
400
0.6
450
0
Output Current(mA)
20
40
60
80
100
120
140
160
Output Current(mA)
No Load Input Current vs. Inpout Voltage
( VOUT=3.3V;Ta=25℃;No load)
Maximum Output Current vs. Input Voltage
(L=4.7uH,Ta=25℃)
400
700
300
VOUT=3.3V
500
Input Current(uA)
Maximum Output Current(mA)
350
600
400
VOUT=5V
300
200
250
200
150
100
100
50
0
0.5
1
1.5
2
2.5
Input Voltage(V)
3
3.5
4
0
1.5
1.8
2.1
2.4
2.7
3
Input Voltage(V)
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BL8542B
TYPICAL PERFORMANCE CHARACTERISTICS
o
Typical values are tested at TA=25 C, unless otherwise specified.
VREF(T)/VREF(T=20℃) vs. Temperature
Output Voltage vs. Temerature
1.006
3.25
1.002
3.24
0.998
3.23
Output Voltage(V)
Normalized VREF
1.01
0.994
0.99
0.986
0.982
3.22
3.21
3.2
3.19
0.978
3.18
0.974
3.17
0.97
-45
-45
-25
-5
15
35
55
75
95
Temerature(℃)
-25
-5
15
35
55
75
95
Temerature(℃)
Frequency vs. Temperature
1100
Frequency(kHz)
1000
900
800
700
600
-45
-25
-5
15
35
55
75
95
Temperature(℃)
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BL8542B
PACKAGE OUTLINE DIMENSION
Package
Devices per reel
Package
Devices per reel
SOT23-5
3000
SOT89-3
1000
Dimension (mm)
Dimension (mm)
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