SEA05
Advanced constant voltage and constant current controller
Features
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Constant voltage and constant current control
Wide operating V
CC
range [3.5 - 36] 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
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
2.5 V
1.23 V
Vcc
6
Applications
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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 op-
amps (with OR-ed open-drain outputs), and a low-
side 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
Table 1.
+
-
+
-
5
3
Out
Vctrl
2
1
Isense
Gnd
4
Ictrl
Device summary
Package
SOT23-6L
Packing
Tape and reel
Order code
SEA05TR
April 2010
Doc ID 17014 Rev 1
1/10
www.st.com
10
Pin description
SEA05
1
Pin description
Figure 2.
Pin configuration
Isense
GND
Vctrl
Note:
1
2
3
6
5
4
Vcc
Out
Ictrl
The adjacent pins have the same AMR to increase the robustness of the IC against
accidental short circuit among pins.
Table 2.
n.
1
Pin description
Name
Isense
Function
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.
Supply Voltage of the device. A small bypass capacitor (0.1 µF typ.) to GND,
located as close to IC’s pins as possible, might be useful to get a clean supply
voltage.
2
GND
3
4
Vctrl
Ictrl
5
OUT
6
Vcc
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Doc ID 17014 Rev 1
SEA05
Maximum ratings
2
Maximum ratings
Table 3.
Symbol
Vcc
Vout
Iout
Ictrl
Isense
Vctrl
Absolute maximum ratings
Pin
6
5
5
4
1
3
Dc supply voltage
Open-drain voltage
Max sink current
Analog input
Analog input
Analog input
Parameter
Value
-0.3 to 38
-0.3 to Vcc
20
-0.3 to Vcc
-0.3 to 3.3
-0.3 to 3.3
Unit
V
V
mA
V
V
V
Table 4.
Symbol
R
thJA
Tj
op
T
STG
Thermal data
Parameter
Thermal resistance, junction-to-ambient
Junction temperature operating range
Storage temperature
Value
250
-40 to 150
°C
-55 to 150
Unit
°C/W
3
Typical application schematic
Figure 3.
Typical application schematic
0.1μF
Vcc
2.5 V
1.23 V
6
R1
5 Out
3 Vctrl
Vo
+
-
+
-
1
0V
2
Gnd
R2
4
-50 mV
Ictrl
Vcsth
Rsense
Io
Isense
V
O
=
R
1
+
R
2
* 2.5
V
R
2
I
O
max
=
0 .05
V
R
sense
Doc ID 17014 Rev 1
3/10
Electrical characteristics
SEA05
4
Electrical characteristics
-25 °C <T
J
< 125 °C, V
CC
= 20 V; unless otherwise specified
Table 5.
Symbol
Device supply
Vcc
Icc
Voltage operating range
Quiescent current (Ictrl =I
sense = 0 V, OUT = open)
3.5
200
36
300
V
µA
Electrical characteristics
Parameter
Test condition
Min.
Typ.
Max.
Unit
Voltage control loop op-amp
Gm
v
V
ctrl
Ibias
Transconductance
(sink current only)
(1)
Voltage reference default
value
(2)
Inverting input bias current
T
J
= 25 °C
1
2.488
2.48
25
3.5
2.5
2.512
V
2.52
nA
S
Current control loop
Gm
i
V
Transconductance
(sink current only)
(3)
Current sense threshold
V
csth
= V
(Isense)
-V
(Ictrl)
(4)
@ I
(Iout)
= 1 mA
Non-inverting input source
current @ V(Ictrl) = -50 mV
1.5
7
S
csth
46
50
54
mV
Ibias
6
µA
Output stage
V
OUTlow
Low output level @ 2 mA
sink current
200
400
mV
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.
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Doc ID 17014 Rev 1
SEA05
Application information
5
Application information
Figure 4.
Application information
Note:
A 15
Ω
resistor in series to Ictrl pin helps to protect the IC in case of negative voltage that
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
o
. If an abrupt
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
sense
pin and therefore the Ictrl pin is pulled
down to –Vo. This could damage the IC in case the Ictrl pin AMR is violated.
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
ctrl
current = Ibias = 6 µA and therefore the error
6 µA x 15
Ω
= 80 µV, the error is 80 µV / 50 mV = 0.16%
Doc ID 17014 Rev 1
5/10
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