Features
-
-
V
V
V
SEA05
Advanced constant voltage and constant current controller
■ Constant voltage and constant current control
■ Wide operating V
■ Low quiescent consumption: 200 µA
■ Voltage reference: 2.5 V
■ Voltage control loop accuracy +/- 0.5%
■ Current sense threshold: 50 mV
■ Open-drain output stage
■ Low external component count
■ SOT23-6L micro package
range [3.5 - 36] V
CC
Applications
■ Battery chargers
■ AC-DC adapters
■ LED drivers
Description
The SEA05 is a highly integrated solution for
SMPS applications requiring a dual control loop to
perform CV (constant voltage) and CC (constant
current) regulation.
The device integrates a voltage reference, two opamps (with OR-ed open-drain outputs), and a lowside current sensing circuit.
The voltage reference, along with one op-amp, is
the core of the voltage control loop; the current
sensing circuit and the other op-amp make up the
current control loop.
The external components needed to complete the
two control loops are: a resistor divider that
senses the output of the power supply and fixes
the voltage regulation setpoint at the specified
value; a sense resistor that feeds the current
sensing circuit with a voltage proportional to the
dc output current; this resistor determines the
current regulation setpoint and must be
SOT23 - 6L
adequately rated in terms of power dissipation;
the frequency compensation components (R-C
networks) for both loops.
The device, housed in one of the smallest
available package, is ideal for space-shrunk
applications such as adapters and chargers.
Figure 1. Internal schematic
cc
2.5
1.23 V
6
5
+
Out
ctrl
3
+
2
Gnd
14
Ictrl Isense
Table 1. Device summary
Order code Package Packing
SEA05TR SOT23-6L Tape and reel
April 2010 Doc ID 17014 Rev 1 1/10
www.st.com
10
Pin description SEA05
t
1 Pin description
Figure 2. Pin configuration
6
6
6
Isense
1
1
1
1
6
Vcc
GND
Vctrl
Note: The adjacent pins have the same AMR to increase the robustness of the IC against
accidental short circuit among pins.
Table 2. Pin description
n. Name Function
1 Isense
2GND
3Vctrl
4Ictrl
5OUT
Inverting input of the current loop op-amp. The pin is tied to the cold end of the
current sense resistor through a decoupling resistor.
Ground. Return of the bias current of the device. 0 V reference for all voltages.
The pin should be tied as close to the ground output terminal of the converter as
possible to minimize load current effect on the voltage regulation setpoint.
Inverting input of the voltage loop op-amp. The pin is tied to the mid-point of a
resistor divider that senses the output voltage.
Non-inverting input of the current loop op-amp. It is tied directly to the hot
(negative) end of the current sense resistor
Common open-drain output of the two internal op-amps. The pin, able to sink
current only, is connected to the branch of the optocoupler’s photodiode to
transmit the error signal to the primary side.
2
2
2
2
3
3
3
3
5
5
5
5
4
4
4
4
Ou
Ictrl
Supply Voltage of the device. A small bypass capacitor (0.1 µF typ.) to GND,
6Vcc
2/10 Doc ID 17014 Rev 1
located as close to IC’s pins as possible, might be useful to get a clean supply
voltage.
SEA05 Maximum ratings
V
Vo
-
-
V
V
o
R
2 Maximum ratings
Table 3. Absolute maximum ratings
Symbol Pin Parameter Value Unit
Vcc 6 Dc supply voltage -0.3 to 38 V
Vout 5 Open-drain voltage -0.3 to Vcc V
Iout 5 Max sink current 20 mA
Ictrl 4 Analog input -0.3 to Vcc V
Isense 1 Analog input -0.3 to 3.3 V
Vctrl 3 Analog input -0.3 to 3.3 V
Table 4. Thermal data
Symbol Parameter Value Unit
R
Tj
T
Thermal resistance, junction-to-ambient 250 °C/W
thJA
Junction temperature operating range -40 to 150
op
Storage temperature -55 to 150
STG
3 Typical application schematic
Figure 3. Typical application schematic
0.1μF
cc
2.5 V
-50 mV
1.23
+
0 V
+
Ictrl Isense
5
3
2
14
°C
R1
Out
Vctrl
Gnd
R2
csth
Rsense
I
O 5.2*
V
=
21
RR
+
2
V
O
max =
VI05.0
sense
R
Doc ID 17014 Rev 1 3/10
Electrical characteristics SEA05
4 Electrical characteristics
-25 °C <TJ < 125 °C, VCC = 20 V; unless otherwise specified
Table 5. Electrical characteristics
Symbol Parameter Test condition Min. Typ. Max. Unit
Device supply
Vcc Voltage operating range 3.5 36 V
Icc
Voltage control loop op-amp
Quiescent current (Ictrl =I
sense = 0 V, OUT = open)
200 300 µA
Gm
V
Transconductance
v
(sink current only)
Voltage reference default
value
(2)
ctrl
(1)
13.5 S
TJ = 25 °C 2.488 2.5 2.512
V
2.48 2.52
Ibias Inverting input bias current 25 nA
Current control loop
Gm
V
csth
Ibias
Transconductance
i
(sink current only)
Current sense threshold
V
= V
csth
@ I
(Iout)
(Isense)-V(Ictrl)
= 1 mA
(4)
Non-inverting input source
current @ V(Ictrl) = -50 mV
(3)
1.5 7 S
46 50 54 mV
6µA
Output stage
V
OUTlow
Low output level @ 2 mA
sink current
1. If the voltage on Vctrl (the negative input of the amplifier) is higher than the positive amplifier input, and it is
increased by 1 mV, the sinking current at the output OUT is increased by 3.5 mA.
2. The internal voltage reference is set at 2.5 V. The voltage control loop precision takes into account the
cumulative effects of the internal voltage reference deviation as well as the input offset voltage of the
transconductance operational amplifier. The internal Voltage Reference is fixed by bandgap, and trimmed
to 0.48 % accuracy at room temperature.
3. When the positive input at Ictrl is lower than -50 mV, and the voltage is decreased by 1 mV, the sinking
current at the output out is increased by 7 mA.
4. Considering Ictrl pin directly connected to the hot (negative) end of the current sense resistor and Isense
pin connected to the cold end of the current sense resistor through a decoupling resistor (see fig.3), the
internal current sense threshold is triggered when the voltage on pin Ictrl is -50 mV. The current loop
reference precision takes into account the cumulative effects of the internal voltage reference deviation as
well as the input offset voltage of the transconductance operational amplifier.
200 400 mV
4/10 Doc ID 17014 Rev 1
SEA05 Application information
)
5
5 Application information
Figure 4. Application information
ȝ
Note: A 15
exceed the AMR of Ictrl pin.
As example a potential dangerous phenomenon could happen during converter output
short-circuit.
Consider the steady state operation of the circuit during voltage mode regulation (i.e. the
output is at its nominal voltage). The output capacitor is fully charged at V
short (i.e. with negligible impedance) is applied at the output, instantly the positive pin of the
electrolytic capacitor is connected to the SEA05 ground. Since the capacitor acts like a
battery, all its voltage is applied across the R
down to –Vo. This could damage the IC in case the Ictrl pin AMR is violated.
9FF
9
9
9
P9
Ω
resistor in series to Ictrl pin helps to protect the IC in case of negative voltage that
,FWUO ,VHQVH
9FVWK
5VHQVH
,
2XW
9FWUO
*QG
55
2
9
pin and therefore the Ictrl pin is pulled
sense
9
5
9R
5
2
PD[ #
. If an abrupt
o
9,
VHQVH
5
In reality the short is not so severe because it has a some impedance, the electrolytic
capacitor has an ESR and it starts discharging as soon as the short is applied. The Ictrl pin
is brought to a negative voltage anyway. The pin internal structure has been design to be
robust against negative voltage but, since the severity of this phenomenon is proportional to
the output voltage, for some applications an external resistor in series with Ictrl pin helps
protect the IC.
The resistor added in series with Ictrl pin introduces an error in the current sense threshold
voltage.
This error can be calculated considering the Ictrl pin current: this current multiplied by the
value of the external resistor gives the current sense threshold variation.
As example if we add a 15 Ω resistor in series to Ictrl pin, we have
I
current = Ibias = 6 µA and therefore the error
ctrl
6 µA x 15 Ω = 80 µV, the error is 80 µV / 50 mV = 0.16%
Doc ID 17014 Rev 1 5/10
Voltage and current control SEA05
h
=
∗
6 Voltage and current control
6.1 Voltage control
The voltage loop is controlled via a first transconductance operational amplifier, the voltage
divider R1, R2, and the optocoupler which is directly connected to the output. Its possible to
choose the values of R1 and R2 resistors using Equation 1-2:
Equation 1
)RR(
+
21
R
2
Equation 2
VctrlV
o
∗=
where Vo is the desired output voltage.
As an example, with R1 = 100 kΩ and R2 = 15 kΩ Vo = 19.17 V
6.2 Current control
The current loop is controlled via the second trans-conductance operational amplifier, the
sense resistor R
Equation 3
Equation 4
where I
is the desired limited current, and V
omax
control loop.
, and the optocoupler. The control equation verifies:
sense
∗=
RR
21
IR
maxosense
R =
sense
−
O
)VctrlV(
Vctrl
Vcst
Vcsth
I
maxo
is the threshold voltage for the current
csth
As an example, with I
Note that the R
sense
omax
= 1 A, V
= 50 mV, then R
csth
sense
= 50 m Ω.
resistor should be chosen taking into account the maximum dissipation
(Plim) through it during full load operation.
Equation 5
P
As an example, with I
= 1 A, and V
omax
LimVcsthlomax
csth
⋅=
= 50 mV, Plim = 50 mW.
Therefore, for most adaptor and battery charger applications, it is suitable a low power
resistor to make the current sensing function.
6/10 Doc ID 17014 Rev 1
SEA05 Compensation
(
)
(
)
V
threshold is achieved internally by a voltage divider tied to an internal voltage
csth
reference. Its middle point is tied to the positive input of the current control operational
amplifier, and its foot has to be connected to lower potential point of the sense resistor as
shown in
Figure 4. The resistors of this voltage divider are matched to provide the best
possible precision. The current sinking outputs of the two trans-conductance operational
amplifiers are common (to the output of the IC). 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.
(with power supply of the device independent from the output voltage)
Figure 5. Output voltage versus output current
V
Vo
Vo l tag e reg ul ati o n
Vo l tag e reg ul ati o n
Current regulation
Current regulation
7 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 as shown in
Vcc of the device indepe nde nt from output voltage
Vcc of the device indepe nde nt from output voltage
Figure 4.
Io
Io
Doc ID 17014 Rev 1 7/10
Package mechanical data SEA05
8 Package mechanical data
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK
specifications, grade definitions and product status are available at:
ECOPACK
Table 6. SOT23-6L mechanical data
θ (degrees) 0° 10° 0° 10°
®
packages, depending on their level of environmental compliance. ECOPACK®
®
is an ST trademark.
www.st.com.
mm. inch
Dim.
Min. Typ. Max. Min. Typ. Max.
A 0.9 1.45 0.035 0.057
A1 0 0.1 0 0.0039
A2 0.9 1.3 0.035 0.0512
b 0.35 0.5 0.014 0.02
c 0.09 0.2 0.004 0.008
D 2.8 3.05 0.11 0.120
E 1.5 1.75 0.059 0.0689
e 0.95 0.037
H 2.6 3 0.102 0.118
L 0.1 0.6 0.004 0.024
Note: Dimensions per JEDEC MO178AB
Figure 6. SOT23-6L package dimensions
8/10 Doc ID 17014 Rev 1
SEA05 Revision history
9 Revision history
Table 7. Document revision history
Date Revision Changes
26-Apr-2010 1 Initial release.
Doc ID 17014 Rev 1 9/10
SEA05
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