Description
SE1051 is a highly integrated solution for SMPS
applications requiring CV (constant voltage) and CC
(constant current) modes.
SE1051 integrates one voltage reference, two
operational amplifiers (the outputs are OR’ed
together, common collectors), and a current
sensing circuit.
The
voltage
reference,
together
with
one
operational amplifier, makes it an ideal voltage
controller.
The other low voltage reference,
together with another operational amplifier, makes it
an ideal current limiter for low side output current
sensing. The current threshold is fixed, and precise.
The SE1051, housed in space-saving SOT23-6L
package, is ideal for space sensitive applications
such as adapters, cellphone chargers, Digital
Camera chargers, and other battery chargers.
Features
Constant Voltage and Constant Current Control
Low Voltage Operation at 3V
Precision Internal Voltage Reference
Low External Component Count
Current Sink Output Stage
Easy Compensation
Low AC Mains Voltage Rejection
Rugged 2KV ESD withstand capability.
Available in SOT-23-6L Package.
RoHS Compliant and 100% Lead (Pb)-Free
Application
Adapters
Digital Camera Chargers.
Cellphone Chargers.
Other Battery Chargers
Ordering Information/Making Information
Device
Package
SOT-23-6L
(Lead-free)
V
OUT
Fixed output voltages
1.21V
Pin Configuration
SE1051
Package
Making Information
PIN1 is down in the left-hand corner.
The last character is the batch
number.
A dot on top right corner is for
lead-free process.
Pin Description
Name
V
CTRL
GND
V
OUT
I
CTRL
V
SENSE
V
CC
Pin#
1
2
3
4
5
6
Type
Analog Input
Power Supply
Current Sink Output
Analog Input
Analog Input
Power Supply
Function
Input Pin of the Voltage Control Loop
Ground Line. 0V Reference For All Voltages
Output Pin. Sinking Current Only
Input Pin of the Current Control Loop
Input Pin of the Current Control Loop
Positive Power Supply Line
Revision 12/4/2008
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 1
Absolute Maximum Rating
Symbol
V
CC
V
IN
θ
JA
T
J
T
STG
T
LEAD
DC Supply Voltage
Input Supply Voltage
Thermal Resistance Junction to Ambient
Operating Junction Temperature Range
Storage Temperature Range
Lead Temperature (Soldering 10 Sec)
Parameter
Maximum
18
-0.3~ V
CC
250
0 to 125
-40 to 150
260
Units
V
V
°C/W
°C
°C
°C
Electrical Characteristic
V
CC
= 5.0V, T
A
= 25°C, unless otherwise specified.
Symbol
Parameter
Test Condition
Min
Typ
Max
Unit
Total Current Consumption
I
CC
Total Supply Current - not taking the output sinking
current into account
Voltage Control Loop
Gmv
Transconduction Gain (V
CTRL
). Sink Current Only
1)
0 < T
A
< 85°C
V
REF
Voltage Control Loop Reference
2)
0 < T
A
< 85°C
I
IBV
Input Bias Current (V
CTRL
)
0 < T
A
< 85°C
Current Control Loop
Gmi
V
SENSE
Transconduction Gain (I
CTRL
). Sink Current Only
3)
Current Control Loop Reference
4)
0 < T
A
< 85°C
I
OUT
= 2.5mA
0 < T
A
< 85°C
I
IBI
Current out of pin I
CTRL
at -200mV
0 < T
A
< 85°C
Output Stage
V
OL
I
OS
Low output voltage at 10 mA sinking current
Output Short Circuit Current. Output to V
CC
. Sink
Current Only
0 < T
A
< 85°C
0 < T
A
< 85°C
300
22
35
mV
mA
25
50
μA
2.9
240
mA/mV
mV
50
100
nA
2.4
2.0
1.21
V
mA/mV
0 < T
A
< 85°C
0.4
0.5
mA
1. If the voltage on V
CTRL
(the negative input of the amplifier) is higher than the positive amplifier input
(V
REF
=1.210V), and it is increased by 1mV, the sinking current at the output OUT will be increased by 2.4mA.
2. The internal Voltage Reference is set at 1.210V. The internal Voltage Reference is fixed by bandgap, and
trimmed to 0.5% accuracy at room temperature.
3. When the positive input at I
CTRL
is lower than -240mV, and the voltage is decreased by 1mV, the sinking current at
the output OUT will be increased by 2.9mA.
4. The internal current sense threshold is set to -240mV. The current control loop precision takes into account the
cumulative effects of the internal voltage reference deviation as well as the input offset voltage of the
trans-conduction operational amplifier.
Revision 12/4/2008
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 2
Block Diagram
1.21
0V
Vcc
Vout
VCL
Vctrl
240mV
CCL
GND
Ictrl
Typical Application
Vsense
Rs
SE1051
1.210
V
Cs
240mV
CCL
To prim ry
a
R2
Rout
C2
22
pF
Cic1
2.2nF
Ric1
R1
Rvc1
Cvc1
2.2nF
Vout+
Vcc
VCL
Vout
Vctrl
Lo
ad
GND
Ictrl
Vsense
Rsen
se
Ric2
Vout-
Fig.1 Typical Adapter or Battery Charger Application Using SE1051
In the above application schematic, the SE1051 is used on the secondary side of a flyback adapter (or battery
charger) to provide an accurate control of voltage and current. The above feedback loop is made
with an optocoupler.
V
OUT
=
V
REF
×
I
LIMIT
=
Revision 12/4/2008
R
1
+
R
2
R
1
V
SENSE
R
SENSE
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 3
Application Hints
Voltage Control
The voltage loop is controlled via a first
transconductance operational amplifier, the
resistor bridge R1, R2, and the optocoupler which
is directly connected to the output.
The relation between the values of R1 and R2
should be chosen as written in Equation 1.
R1 = R2 x Vref / (Vout - Vref)
Eq1
The current sinking outputs of the two
trans-conductance operational amplifiers are
connected together. This makes an ORing
function which ensures that whenever the current
or the voltage reaches too high values, the
optocoupler is activated.
The relation between the controlled current and
the controlled output voltage can be described
with a square characteristic as shown in the
following V/I output-power graph.
Where Vout is the desired output voltage. To
avoid the discharge of the load, the resistor bridge
R1, R2 should be highly resistive. For this type of
application, a total value of 100KΩ (or more)
would be appropriate for the resistors R1 and R2.
As an example, with R2 = 100KΩ, Vout = 4.10V,
Vref = 1.210V, then R1 = 41.9KΩ.
Note that if the low drop diode should be inserted
between the load and the voltage regulation
resistor bridge to avoid current flowing from the
load through the resistor bridge, this drop should
be taken into account in the above calculations by
replacing Vout by (Vout + Vdrop).
Current Control
The current loop is controlled via the second
trans-conductance operational amplifier, the
sense resistor Rsense, and the optocoupler.
The control equation is:
Rsense x I-limit = Vsense
Eq2
Rsense = Vsense / I-limit
Eq3
where I-limit is the desired current limit, and
Vsense is the threshold voltage for the current
control loop.
As an example, with I-limit = 1A, Vsense =
-240mV, then Rsense = 240mΩ.
Note that the Rsense resistor should be selected
with the consideration of the Maximum Power in
full load operations (P-limit).
P-limit = Vsense x I-limit.
Eq4
As an example, with I-limit = 1A, and Vsense
=-240mV, P-limit = 240mW.
Consequently, for most adapter and battery
charger applications, a quarter-watt resistor to
make the current sensing function is sufficient.
Vsense threshold is achieved internally by a
resistor bridge tied to the Vref voltage reference.
Its middle point is tied to the positive input of the
current control operational amplifier, and its foot is
to be connected to lower potential point of the
sense resistor as shown on the following figure.
The resistors of this bridge are matched in layout
to provide the best precision possible.
Revision 12/4/2008
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 4
Fig.2 Output voltage versus output current
Compensation
The
voltage-control
trans-conductance
operational amplifier can be fully compensated.
Both of its output and negative input are directly
accessible
for
external
compensation
components.
An example of a suitable compensation network
is shown in Fig.1. It consists of a capacitor
Cvc1=2.2nF and a resistor Rcv1=470KΩ in
series, connected in parallel with another
capacitor Cvc2=22pF.
The
current-control
trans-conductance
operational amplifier can also be fully
compensated. Both of its output and negative
input are directly accessible for external
compensation components.
An example of a suitable compensation network
is shown in Fig.1. It consists of a capacitor
Cic1=2.2nF and a resistor Ric1=22KΩ in series.
When the Vcc voltage reaches 12V it could be
interesting to limit the current coming through the
output in the aim to reduce the dissipation of the
device and increase the stability performances of
the whole application.
An example of a suitable Rout value could be
330Ω in series with the opto-coupler in case
Vcc=12V.
Start Up and Short Circuit Conditions
Under start-up or short-circuit conditions the SE1051 does not have a high enough supply voltage. This is due
to the fact that the chip has its power supply line in common with the power supply line of the charger system.
Consequently, the current limitation can only be ensured by the primary PWM module, which should be
designed accordingly.
If the primary current limitation is considered not to be precise enough for the application, then a sufficient
supply for the SE1051 has to be ensured under any condition. It would then be necessary to add some
circuitry to supply the chip with a separate power line. This can be achieved in numerous ways, including an
additional winding on the transformer.
The following schematic shows how to realize a low-cost power supply for the SE1051 (with no additional
windings).
Please pay attention to the fact that in the particular case presented here, this low-cost power supply can
reach voltages as high as twice the voltage of the regulated line. Since the Absolute Maximum Rating of the
SE1051 supply voltage is 18V, this low-cost auxiliary power supply can only be used in applications where
the regulated line voltage does not exceed 9V.
SE1051
1.210
V
Rs
Cs
240mV
CCL
To prim ry
a
R2
Rout
C2
22
pF
Cic1
2.2nF
Rvc1
Cvc1
2.2nF
Vout+
Vcc
Vout
VCL
Vctrl
GND
Ictrl
Vsense
Ric1
R1
Rsen
se
Ric2
Vout-
Fig. 3
Revision 12/4/2008
Preliminary and all contents are subject to change without prior notice.
© Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 5
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