ST SEA05L User Manual

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Advanced constant voltage and constant current controller

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)

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

GND

Isense

OSC

Out

ctrl

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

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

Vout 5 Open-drain voltage –0.3 to V

Iout 5 Max. sink current 20 mA

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

th j-amb

Tstg Storage temperature –55 to 150

Figure 2. Pin configuration

6 DC supply voltage –0.3 to 38 V

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

Vcc

< 12

(1)

°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.

Doc ID 18462 Rev 1 3/12

Out

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

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

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

supply voltage.

4/12 Doc ID 18462 Rev 1

SEA05L Operation

Table 5. Electrical characteristics (–25 C° < Tj < 125 °C, VCC = 20 V; unless otherwise specified)

Symbol Parameter Test condition Min. Typ. Max. Unit

Device supply

Voltage operating range 3.5 36 V

Quiescent current

(Ictrl = Vsense = 0, OUT = open)

250 500 µA

Voltage control loop op-amp

(2)

(1)

13.5 S

Tj = 25 °C 2.488 2.5 2.512 V

Transconductance (sink current only)

Vctrl Voltage reference default value

Ibias Inverting input bias current 25 nA

Current control loop

csth

Transconductance (sink current only)

Current sense threshold at I(Iout) = 1 mA

(3)

(4)

1.5 7 S

48 50 52 mV

Ibias Non-inverting input source current 6 µA

Output stage

OUTlow

Low output level at 2 mA sink current 200 400 mV

LED driver

LED driver sink current capability (peak) 10 mA

LED driver current modulation frequency 0.6 1 1.4 kHz

LD_LKG

1. If the voltage on Vctrl (the negative input of the amplifier) is higher than the positive amplifier input, and it is increased by

2. The internal voltage reference is set at 2.5 V. The voltage control loop precision takes into account the cumulative effects of

3. When the inverting input at Isense is greater than 50 mV, and the voltage is increased by 1 mV, the sinking current at the

4. The internal current sense threshold is triggered when the voltage on pin Isense is 50 mV. The current control loop

Low output level at 5 mA sink current

LDlow

(internal mosfet on)

LED driver leakage current (internal mosfet off)

1mV, the sinking current at the output OUT will be increased by 3.5 mA.

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.

output Out will be increased by 7 mA.

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.

450 900 mV

0.5 µA

Doc ID 18462 Rev 1 5/12

Application information SEA05L

2 Application information

Figure 3. Typical application schematic

0.1μF LED

1.23 V

2.5 V

50mV

GND

Rsense

Isense

OSC

2.1 Voltage and current control

Voltage control

Out

05.0

sense

AM04986v1

ctrl

5.2*

max

The voltage loop is controlled via a transconductance operational amplifier, the voltage divider R choose the values of R

, R2, and the optocoupler which is directly connected to the output. It is possible to

and R2 resistors using Equation 1 and Equation 2:

Equation 1

)(

VctrlV

∗=

Equation 2

)(

VctrlV

where V

As an example, with R

6/12 Doc ID 18462 Rev 1

∗=

Vctrl

is the desired output voltage.

= 100 kΩ and R2 = 15 kΩ VO = 19.17 V.

SEA05L Application information

Current control

The current loop is controlled via a transconductance operational amplifier, the sense resistor R

The control equation verifies:

Equation 3

Equation 4

sense

, and the optocoupler.

sense

VIR =∗

max

csthOsense

csth

maxO

where I control loop. As an example, with I

Note that the R (P

) through it during full load operation.

lim

is the desired limited current, and V

Omax

omax

resistor should be chosen, taking into account the maximum dissipation

sense

= 1 A, V

is the threshold voltage for the current

csth

= 50 mV, then R

csth

sense

= 50 mΩ.

Equation 5

IVP ∗=

maxlim Ocsth

As an example, with I

= 1 A and V

Omax

= 50 mV, P

csth

= 50 mW.

lim

Therefore, for most adaptor and battery charger applications, a low-power resistor is suitable for the current sensing function.

threshold is achieved internally by a voltage divider tied to an internal precise voltage

csth

reference. Its midpoint is tied to the positive input of the current control operational amplifier, and its endpoint is connected to GND. The resistors of this voltage divider are matched to provide the best precision possible. The current sinking outputs of the two transconductance operational amplifiers are common (to the output of the IC). This makes an OR function which ensures that whenever the current or the voltage reaches excessively high values, the optocoupler is activated.

The relationship 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).

Doc ID 18462 Rev 1 7/12

Application information SEA05L

Figure 4. Output voltage versus output current

Vout

Voltage regulation

Current regulation

2.2 Compensation

The voltage control transconductance operational amplifier can be fully compensated. Both its output and negative input are directly accessible for external compensation components.

2.3 LD pin function

The device provides a unique feature that allows highly efficient driving of an LED pilot-lamp. The main benefit of this new feature is to allow reducing the standby power consumption of the SMPS with the LED pilot-lamp.

The LD pin is an open-drain output able to sink 5 mA (peak), driven by the internal oscillator at 1 kHz (typ.) square waveform with 12.5% duty cycle (see Figure 6). The internal mosfet starts to switch when V impedance) when V

Connecting the LED pilot-lamp, with a resistor in series in order to limit the LED current, to pin LD (as shown in Figure 5) reduces the power consumption of the LED while keeping the same driving peak current. The LED driving current modulation frequency of 1 kHz (typ.) eliminates the visual perception of flickering.

(

Vcc of the device independent from output voltage)

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

Iout

is below the UVLO of the IC.

AM04987v1

8/12 Doc ID 18462 Rev 1

SEA05L Application information

Figure 5. Connection of LED to pin LD

1.23 V

GND

2.5 V

50mV

1 2

Isen se

OSC

LED

Out

Vctrl

LED

Figure 6. LED current waveform with a typical frequency of 1 kHZ

T=1ms (f=1kHz)

ton=125 µs (T/8)

LED

AM04988v1

AM04989v1

Doc ID 18462 Rev 1 9/12

Package mechanical data SEA05L

3 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: www.st.com. ECOPACK

Table 6. SOT23-6L (2.90 mm x 2.80 mm) package mechanical data

packages, depending on their level of environmental compliance. ECOPACK®

is an ST trademark.

Sym

Min Typ Max Min Typ Max

A 1.45 0.057

A1 0.00 0.15 0.000 0.006

A2 0.90 1.15 1.30 0.035 0.045 0.051

b 0.30 0.50 0.012 0.020

c 0.08 0.22 0.003 0.009

D 2.90 0.114

E 2.80 0.110

E1 1.60 0.063

e 0.95 0.037

e1 1.90 0.075

L 0.30 0.45 0.60 0.012 0.018 0.024

è 0° 4° 8° 0° 4° 8°

N 6 6

mm inches

Note: Dimensions per JEDEC MO178AB

Figure 7. SOT23-6L (2.90 mm x 2.80 mm) package mechanical drawing

10/12 Doc ID 18462 Rev 1

7049717_G

SEA05L Revision history

4 Revision history

Table 7. Document revision history

Date Revision Changes

23-Feb-2011 1 Initial release.

Doc ID 18462 Rev 1 11/12

SEA05L

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12/12 Doc ID 18462 Rev 1

ST SEA05L User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Table 1. Device summary

1 Operation

Table 2. Absolute maximum ratings

Table 3. Thermal data

Figure 2. Pin configuration

Table 4. Pin functions

2 Application information

Figure 3. Typical application schematic

2.1 Voltage and current control

Figure 4. Output voltage versus output current

2.2 Compensation

2.3 LD pin function

Figure 5. Connection of LED to pin LD

Figure 6. LED current waveform with a typical frequency of 1 kHZ

3 Package mechanical data

Table 6. SOT23-6L (2.90 mm x 2.80 mm) package mechanical data

Figure 7. SOT23-6L (2.90 mm x 2.80 mm) package mechanical drawing

4 Revision history

Table 7. Document revision history