BL8531C

BL8531C
High Efficiency, Multi-Function Step-up DC/DC Controller
DESCRIPTION
FEATURES

BL8531C series are CMOS-based PFM step-up DCDC Controller with low supply current and high
output voltage accuracy. Quiescent current
drawn from power source is as low as 6uA. It is
capable of delivering 500mA output current at
4.0V output with 2V input Voltage. Only four
external components are necessary: An inductor,
a Schottky diode, an output filter capacitor and a
NMOSFET or a NPN transistor All of these
features make BL8531C series be suitable for the
portable devices, which are supplied by a single
battery to four-cell batteries.
BL8531C has a drive pin (EXT) for external
transistor. So it is possible to load a large output
current with a power transistor which has a low
voltage dropout.
BL8531C integrates stable reference circuits and
trimming technology, so it can afford high
precision and low temperature-drift coefficient of
the output voltage.
BL8531C is available in SOT-23-3, SOT-23-5 and
SOT-89-3 packages which are PB free. And in SOT23-5 the device can be switch on or off easily by
CE pin, to minimize the standby supply current.




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
Deliver 500mA at 4.0V Output voltage with
2V input Voltage
The controller output voltage can be adjusted
from 2.5V～6.0V(In 0.1V step)
Output voltage accuracy ---------------------2%
Low temperature-drift coefficient of the
output voltage-----------------------100ppm/C
Only four external components are necessary:
An inductor, a Schottky diode, an output filter
capacitor and a NMOSFET or a NPN transistor
High power conversion efficiency----------90％
Low quiescent current drawn from power
source--------------------------------------------- 6uA
Small package--SOT-23-3, SOT-23-5, SOT-89-3
APPLICATIONS



TYPICAL APPLICATION
Power source for PDA, DSC, MP3 Player,
electronic toy and wireless mouse
Power source for a single or dual-cell batterypowered equipments
Power source for LED
ELECTRICAL CHARACTERISTICS
BL8531C
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1
BL8531C
ORDERING INFORMATION
MARKING INFORMATION
BL8531C □
1□
2□
3□
4
Code
Product Classification
□
1
□
2
□
3
□
4
Description
Marking
3C:Product
Code
Temperature&Rohs:
C: -40~85C , Pb Free Rohs Std.
Package type:
B3: SOT-23-3
B5: SOT-23-5
C3: SOT-89-3
Packing type:
TR: Tape&Reel (Standard)
Output voltage:
e.g. 25=2.5V
56=5.6V
60=6.0V
3CXX
Parameter
Value
Output Voltage Range
EXT Pin Voltage
CE Pin Voltage
Operating Junction Temperature (Tj)
Ambient Temperature (Ta)
SOT-23-3
Power Dissipation
SOT-23-5
SOT-89-3
Storage Temperature (Ts)
Lead Temperature & Time
-0.3V-12V
-0.3V-(VOUT+0.3)
-0.3V-(VOUT+0.3)
125C
-40C -85C
250mW
250mW
500mW
-40C -150C
260C,10S
Note:
Exceed these limits to damage to the device.
Exposure to absolute maximum rating conditions may
affect device reliability.
Value
Suggestion: Use tantalum type capacitor to reduce the
ripple of the output voltage. Use 1nF filter ceramic
type capacitor to connect OUT pin and GND pin. The
filter capacitor is recommended as close as possible to
OUT pin and GND pin.
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2
XX: Output
Voltage
Product Classification
LBXX
LLBYW
CE
GND
OUT
EXT
NC
RECOMMENDED WORK CONDITIONS
0.8V-Vout
10-100uH
≥10uF
47-220uF
-40C -85C
BL8531CCB3TR□ □
Marking
3C:Product
Code
3CXX
Parameter
XX: Output
Voltage
Product Classification
ABSOLUTE MAXIMUM RATING
Input Voltage Range
Inductor
Input Capacitor
Output Capacitor
Ambient Temperature (Ta)
BL8531CCB5TR□ □
BL8531CCC3TR□ □
Marking
LB: Product
Code
XX: Output
Voltage
LL: LOT NO.
B: FAB Code
YW: Date
Code
Chip Enable (Active high)
Ground Pin
Output Pin, Power supply for internal
Switching Pin
No Connection
BL8531C
ELECTRICAL CHARACTERISTICS
Default condition (unless otherwise provided): Vin=0.6×Vout, Iout=10mA, Temperature=25C, Use external circuit in
test circuit list
SYMBOL
ITEM
Vout
Output Voltage
Vin
Iin
Input Voltage
Input Current *(No load)
IDD
Quiescent current *
Istandby
VCEH
VCEL
Chip leakage current
CE “H” threshold voltage
CE “L” threshold voltage
Fosc
Oscillator frequency
IEXTH
EXT”H” output current
IEXTL
EXT”L” output current
Duty
Oscillator duty cycle
TEST CONDITIONS
2.45
2.646
2.94
3.234
3.528
3.92
4.9
5.88
Iout=0mA, Vin=Vout*0.6
No external component,
Vout =Vout×1.05
VCE=0V
VCE: 02V
VCE: 20V
Vout=Vout*0.96
Test EXT pin frequency
3.0V<=Vout<=3.9V
4.0V<=Vout<=4.9V
5.0V<=Vout<=6.9V
3.0V<=Vout<=3.9V
4.0V<=Vout<=4.9V
5.0V<=Vout<=6.9V
On(Vlx“L”)side
Note:
Diode：Schottky type, such as: 1N5817, 1N5819, 1N5822
Inductor: 27uH(R<0.5)
Output capacitor: 100uF(Tantalum type)
Vout pin filter capacitor: 1nF(Ceramic type)
Input capacitor: 47uF
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MIN
3
REFERENCE DATA
TYP.
MAX
2.5
2.7
3.0
3.3
3.6
4.0
5.0
6.0
20
2.55
2.754
3.06
3.366
3.672
4.08
5.1
6.12
12
25
V
uA
6
15
uA
1
uA
V
V
0.8
0.3
70
UNIT
V
400
KHz
-21
-35
-41
23
25
31
75
mA
mA
mA
mA
mA
mA
%
80
BL8531C
BLOCK DIAGRAM
TYPICAL APPLICATIONS
(1) Application with external NMOSFET
Fig 2
(2) Application with external NPN transistor
Fig 3
Note: R1=330Ω, C1=10nF. (R1 can be calculated by load. If load is light R1’s value can be added. If load is heavy R1’s
value can be smaller. )
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BL8531C
DETAILED DESCRIPTION
BL8531C series are boost structure, voltage-type
pulse-frequency modulation(PFM) step-up DC-DC
controller. Only four external components are
necessary: an inductor, a schottky diode, an
output filter capacitor and a NMOSFET or a NPN
transistor. The step-up DC-DC converter,
constructed by BL8531C, can be adjusted from
2.5V to 6.0V, 0.1V step. By using the depletion
technics, the quiescent current drawn from
power source is lower than 8uA. The high
efficiency device consists of resistors for output
voltage detection and trimming, a start-up
voltage circuit, an oscillator, a reference circuit, a
PFM control circuit, a switch protection circuit
and a driver transistor.
the switch current and quiescent current of chip
will effect efficiency certainly. So in very light load
condition, the efficiency will drop. Therefore, it is
recommended that user use BL8531C in the
condition of load current as large as several tens
of mA to several hundreds of mA.
SELECTION OF THE EXTERNAL COMPONENTS
Thus it can be seen, the inductor, schottky diode
and external NMOSFET or NPN transistor. affect
the conversion efficiency greatly. The inductor
and the capacitor also have great influence on
the output voltage ripple of the converter. So it is
necessary to choose a suitable inductor, a
capacitor, an external NMOSFET or NPN
transistor and a right schottky diode, to obtain
high efficiency and low ripple.
BL8531C integrates PFM control system. This
system controls fixed power switch on duty cycle
frequency to stabilize output voltage by
calculating results of other blocks which sense
input voltage, output voltage, output current and
load conditions. In PFM modulation system, the
frequency and pulse width is fixed. The duty cycle
is adjusted by skipping pulses, so that switch ontime is changed based on the conditions such as
input voltage, output current and load. The
oscillate block inside BL8531C provides fixed
frequency and pulse width wave.
Before discussion，we define
D
INDUCTOR SELECTION
Above all, we should define the minimum value
of the inductor that can ensure the boost DC-DC
to operate in the continuous current-mode
condition.
The reference circuit provides stable reference
voltage to output stable output voltage. Because
internal trimming technology is used, the chip
output change less than ±2%. At the same time，
the problem of temperature-drift coefficient of
output voltage is considered in design, so
temperature-drift coefficient of output voltage is
less than 100ppm/℃。
L min 
D (1  D) 2 R L
2f
The above expression is got under conditions of
continuous current mode, neglect Schottky
diode’s voltage, ESR of both inductor and
capacitor. The actual value is greater that it. If
inductor’s value is less than Lmin，the efficiency
of DC-DC converter will drop greatly, and the DCDC circuit will not be stable.
Secondly, consider the ripple of the output
voltage,
High-gain differential error amplifier guarantees
stable output voltage at difference input voltage
and load. In order to reduce ripple and noise, the
error amplifier is designed with high band-with.
D  Vin
Lf
Vin
DVin
Im ax 

2
2 Lf
(1  D) RL
I 
BL8531C has a drive pin (EXT) for external
transistor. So it is possible to load a large output
current with a power transistor and a low
saturation voltage. At very light load condition,
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Vout  Vin
Vout .
5
BL8531C
If inductor value is too small, the current ripple
through it will be great. Then the current through
diode and power switch will be great. Because
the power switch on chip is not ideal switch, the
energy of switch will improve. The efficiency will
fall.
Consider ESR of capacitor，ripple will increase:
r'  r 
When current is large, ripple caused by ESR will be
main factor. It may be greater than 100mV。The
ESR will affects efficiency and increase energy loss.
So low-ESR capacitor (for example: tantalum
capacitor) is recommend or connect two or more
filter capacitors in parallel.
Thirdly ， in general, smaller inductor values
supply more output current while larger values
start up with lower input voltage and acquire
high efficiency.
DIODE SELECTION
An inductor value of 3uH to 1mH works well in
most applications. If DC-DC converter delivers
large output current (for example: output current
is great than 50mA), large inductor value is
recommended in order to improve efficiency. If
DC-DC must output very large current at low
input supply voltage, small inductor value is
recommended.
Rectifier diode will affects efficiency greatly ，
Though a common diode (such as 1N4148) will
work well for light load ， it will reduce about
5%~10% efficiency for heavy load，For optimum
performance, a Schottky diode (such as
1N5817,1N5819,1N5822) is recommended.
INPUT CAPACITOR
The ESR of inductor will effect efficiency greatly.
Suppose ESR value of inductor is rL，Rload is load
resistor，then the energy can be calculated by
following expression :
 
If supply voltage is stable, the DC-DC circuit can
output low ripple, low noise and stable voltage
without input capacitor. If voltage source is far
away from DC-DC circuit, input capacitor value
greater than 10uF is recommended.
rL
Rload (1  D) 2
For example: input 1.5V, output is 3.0V,
Rload=20Ω, rL=0.5Ω, The energy loss is 10%.
Consider all above，inductor value of 47uH、
ESR<0.5Ω is recommended in most applications.
Large value is recommended in high efficiency
applications and smaller value is recommended
Vout~GND FILTER CAPACITOR
Because the chip’s switch current flows from Vout
pin, then through the chip into GND pin. Therefore
if the output capacitor’s two pins were not very
near the chip’s Vout pin and GND pin, Vout ‘s stable
would be affected. User will found that the output
voltage will drop when load grows up if the output
capacitor’s two pin is not very near the chip’s Vout
pin and GND pin. In this condition, 1nF ceramic
capacitor is recommended at very near the chip’s
Vout pin and GND pin. So in all BL8531C application,
two capacitors are needed to obtain stable output
voltage. The 100μF tantalum output capacitor is
recommended to stable output voltage nearby load.
The 1nF Vout pin to GND pin ceramic filter
capacitor is recommended to stable chip’s sense
voltage.
OUTPUT CAPACITOR SELECTION
Ignore ESR of capacitor，the ripple of output
voltage is:
r
Vout
D

Vout
Rload Cf
So large value capacitor is needed to reduce
ripple. But too large capacitor value will slow
down system reaction and cost will improve. So
100uF capacitor is recommended. Larger
capacitor value will be used in large output
current system. If output current is small (<10mA),
small value is needed.
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Im ax  RESR
Vout
6
BL8531C
TEST CIRCUITS
Output voltage test circuit
Fig 4
Quiescent current test circuit
Fig 5
Input Current (no load) test circuit
Fig 6
Oscillator frequency and duty cycle test circuit
Fig 7
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BL8531C
EXTEND APPLICATIONS
12V STEP-UP APPLICATION
Fig 8
Note: BL8531C’s output voltage is 6V. When the output current is small or no load, the output voltage will be unstable,
use the RZD for flowing the bias current through the zener diode. For step-up application, a diode(for example: 1N4148)
is needed as starter circuit.
STEP-DOWN APPLICATION
Fig 9
Note: In step-down application, use starter circuit as above. 2.5V≤Vzener≤Vout. RST is needed for bias current of
zener diode. This starter circuit also can be used in high voltage step-up application.
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BL8531C
FLYBACK STEP-UP/STEP-DOWN APPLICATION
Fig 10
Note: In step-down and step-up/step-down application, starter circuit in fig 8 is need. In step-up application, simpler
starter circuit in fig 9 can be used.
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BL8531C
TYPICAL PERFORMANCE CHARACTERISTICS
(Recommended operating conditions: L=10uH, Cin=47uF, Cout=100uF, Cp=1nF Topt=25C. unless otherwise noted)
BL8531C
BL8531C
BL8531C
BL8531C
BL8531C
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BL8531C
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BL8531C
PACKAGE LINE
Package
SOT-23-3
Devices per reel
3000Pcs
Unit
mm
3000Pcs
Unit
mm
Package dimension：
Package
SOT-23-5
Devices per reel
Package specification：
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BL8531C
Package
SOT-89-3
Devices per reel
Package Dimension:
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12
1000Pcs
Unit
mm