ST SEA05L User Manual

Advanced constant voltage and constant current controller

V

V

CC

with very efficient LED pilot-lamp driver

Features

■ Constant voltage and constant current control

■ Very efficient LED pilot-lamp driver

■ Wide operating V

■ Low quiescent consumption: 250 µA

■ Voltage reference: 2.5 V

■ Voltage control loop accuracy ± 0.5%

■ Current sense threshold: 50 mV

■ Current control loop accuracy ± 4%

■ Low external component count

■ Open-drain output stage

■ SOT23-6L package

Applications

■ AC-DC adapter with LED pilot-lamp

■ Battery chargers with LED pilot-lamp

■ SMPS with LED pilot-lamp

range (3.5 V - 36 V)

CC

SEA05L

Preliminary data

SOT23-6L (plastic package)

Figure 1.

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.

Block diagram

2.5 V

1.23 V

50mV

2

GND

+

-

+

-

1

Isense

6

OSC

5

Out

3

ctrl

4

LD

Description

The external components needed to complete the
two control loops are:

The device is a highly integrated solution for
SMPS applications, with an LED pilot-lamp
requiring a dual control loop to perform CV
(constant voltage) and CC (constant current)
regulation.

The IC allows very efficient LED pilot-lamp driving
which helps to reduce the standby consumption of
the SMPS. It integrates a voltage reference, two
op-amps (with OR-ed open-drain outputs), a low­side current sensing circuit and an LED pilot-lamp
driver pin implemented with an open-drain mosfet

- 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 adequately rated
in terms of power dissipation

- the frequency compensation components (R-C
networks) for both loops.

driven by square waveform with 12.5% duty cycle
at 1 kHz that allows reducing LED consumption.

February 2011 Doc ID 18462 Rev 1 1/12

This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to
change without notice.

The device is ideal for space-critical applications.

Table 1. Device summary

Order code Package Packing

SEA05LTR SOT23-6L Tape & reel

www.st.com

1

Contents SEA05L

Contents

1 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.1 Voltage and current control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2 Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3 LD pin function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2/12 Doc ID 18462 Rev 1

SEA05L Operation

1 Operation

Table 2. Absolute maximum ratings

Symbol Pin Parameter Value Unit

V

CC

Vout 5 Open-drain voltage –0.3 to V

Iout 5 Max. sink current 20 mA

V

LD

I

LD

Isense 1 Analog input –0.3 to V

Vctrl 3 Analog input –0.3 to V

1. Vctrl cannot exceed VCC and cannot exceed 12 V.

Table 3. Thermal data

Symbol Parameter Value Unit

R

th j-amb

Tj

op

Tstg Storage temperature –55 to 150

Figure 2. Pin configuration

6 DC supply voltage –0.3 to 38 V

CC

4 Open-drain voltage –0.3 to V

4 Max. sink current 15 mA

Thermal resistance, junction-to-ambient 250 °C/W

Junction temperature operating range –40 to 150

Isense

1

1

1

1

6

6

6

6

Vcc

CC

CC

CC

< 12

(1)

V

V

V

V

°C

GND

Vctrl

Table 4. Pin functions

Pin number Name Function

Inverting input of the current loop op-amp. The pin is typically used for the

1 Isense

2GND

current control loop, connecting it to the positive 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 has to be tied as close as possible to the ground output
terminal of the converter to minimize load current effect on the voltage
regulation setpoint.

2

2

2

2

3

3

3

3

Doc ID 18462 Rev 1 3/12

5

5

5

5

4

4

4

4

Out

LD

AM04985v1

Operation SEA05L

Table 4. Pin functions (continued)

Pin number Name Function

Inverting input of the voltage loop op-amp. The pin is typically used for the

3Vctrl

4LD

5OUT

6V

voltage control loop and is connected to the midpoint of a resistor divider
that senses the output voltage.

Open-drain output able to sink 5 mA (peak), driven by the internal oscillator
at 1 kHz square waveform with 12.5% duty cycle. The internal mosfet starts
to switch when V

is above the turn-on threshold (typ. 3 V) and it is off (LD

CC

high impedance) when VCC is below the UVLO of the IC. The pin can be
connected to an external LED pilot-lamp with a resistor in series in order to
limit the LED current

Common open-drain output of the two internal op-amps. The pin, only able
to sink current, is typically 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 the IC pins as possible, might be useful to get a clean

CC

supply voltage.

4/12 Doc ID 18462 Rev 1