Datasheet

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Preliminary data

This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to

change without notice.

February 2011 Doc ID 18462 Rev 1 1/12

SEA05L

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

range (3.5 V - 36 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

Description

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 low-

side current sensing circuit and an LED pilot-lamp

driver pin implemented with an open-drain mosfet

driven by square waveform with 12.5% duty cycle

at 1 kHz that allows reducing LED consumption.

Figure 1.

Block diagram

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 adequately rated

in terms of power dissipation

- the frequency compensation components (R-C

networks) for both loops.

The device is ideal for space-critical applications.

Table 1. Device summary

Order code Package Packing

SEA05LTR SOT23-6L Tape & reel

SOT23-6L (plastic package)

Out

ctrl

Isense

1.23 V

2.5 V

50mV

OSC

GND

www.st.com

Summary of content (12 pages)

PAGE 1
SEA05L Advanced constant voltage and constant current controller with very efficient LED pilot-lamp driver Preliminary data Features ■ Constant voltage and constant current control ■ Very efficient LED pilot-lamp driver ■ Wide operating VCC range (3.5 V - 36 V) ■ Low quiescent consumption: 250 µA ■ Voltage reference: 2.5 V ■ Voltage control loop accuracy ± 0.
PAGE 2
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 . . . . . . . . . . .
PAGE 3
SEA05L 1 Operation Operation Table 2. Absolute maximum ratings Symbol Pin VCC 6 Vout Value Unit DC supply voltage –0.3 to 38 V 5 Open-drain voltage –0.3 to VCC V Iout 5 Max. sink current 20 mA VLD 4 Open-drain voltage –0.3 to VCC V ILD 4 Max. sink current 15 mA Isense 1 Analog input Vctrl Parameter 3 –0.3 to VCC –0.3 to VCC < Analog input 12(1) V V 1. Vctrl cannot exceed VCC and cannot exceed 12 V. Table 3.
PAGE 4
Operation SEA05L Table 4. 4/12 Pin functions (continued) Pin number Name Function 3 Vctrl Inverting input of the voltage loop op-amp. The pin is typically used for the voltage control loop and is connected to the midpoint of a resistor divider that senses the output voltage. 4 LD 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 VCC is above the turn-on threshold (typ.
PAGE 5
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 36 V 500 µA Device supply VCC Voltage operating range ICC Quiescent current (Ictrl = Vsense = 0, OUT = open) 3.5 250 Voltage control loop op-amp Gmv Transconductance (sink current only)(1) Vctrl Voltage reference default value Ibias Inverting input bias current (2) Tj = 25 °C 1 3.5 2.488 2.5 S 2.
PAGE 6
Application information SEA05L 2 Application information Figure 3. Typical application schematic 0.1μ F LED 1.23 V V cc 6 2.5 V 5 + - 50m V R1 Out 3 Vo V ctrl + - R2 4 LD 2 1 GND Isen se OSC R sen se Io VO = 2.1 R1 + R 2 * 2.5 V R2 IO max = 0.05 V Rsense AM04986v1 Voltage and current control Voltage control The voltage loop is controlled via a transconductance operational amplifier, the voltage divider R1, R2, and the optocoupler which is directly connected to the output.
PAGE 7
SEA05L Application information Current control The current loop is controlled via a transconductance operational amplifier, the sense resistor Rsense, and the optocoupler. The control equation verifies: Equation 3 Rsense ∗ I O max = Vcsth Equation 4 Rsense = Vcsth I O max where IOmax is the desired limited current, and Vcsth is the threshold voltage for the current control loop. As an example, with Iomax = 1 A, Vcsth = 50 mV, then Rsense = 50 mΩ.
PAGE 8
Application information Figure 4. SEA05L Output voltage versus output current V out C urrent regulation V oltage regulation (V cc of the device independent from output voltage) Iout AM04987v1 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.
PAGE 9
SEA05L Application information Figure 5. Connection of LED to pin LD V cc LED 1.23 V IL E D V cc 6 2.5 V 5 + - 50m V Out R LED 3 V ctrl + - 4 LD 2 1 GND Isen se OSC AM04988v1 Figure 6.
PAGE 10
Package mechanical data 3 SEA05L Package mechanical data In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK® packages, depending on their level of environmental compliance. ECOPACK® specifications, grade definitions and product status are available at: www.st.com. ECOPACK® is an ST trademark. Table 6. SOT23-6L (2.90 mm x 2.80 mm) package mechanical data mm inches Sym Min Typ A Min Typ 1.45 A1 0.00 A2 0.90 b c Max 0.057 0.15 0.000 1.30 0.
PAGE 11
SEA05L 4 Revision history Revision history Table 7. Document revision history Date Revision 23-Feb-2011 1 Changes Initial release.
PAGE 12
SEA05L Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale.