ST STLED25 User Manual

Features

■ Operating input voltage range from 2.3 V to

5.5 V

■ ± 7.5% LED current accuracy

■ Two LEDs in series per channel

■ High side current source

■ Up to 125 mA of total LED current

■ 86% efficiency at 100 mA

■ PWM dimming with automatic shutdown time

window

■ 2.5 MHz switching frequency

■ CSP 12 bumps 0.4 mm. pitch 1.4 x 1.8 mm.

Applications

■ LCD backlight with up to 10 LEDs

■ Cellular phones

■ PDAs

Description

STLED25

5 channels step-up white LED driver

Datasheet − production data

Flip-Chip 12 bumps (1.4 x 1.8 mm.)

continue operating driver channels that are
functioning normally, while avoiding excessive
power consumption or associated thermal issues.
The control technique is able to maintain the
efficiency close to 87% at medium load and
higher than 85% at light or full load. The device
also includes soft-start control, inrush current
limit, thermal shutdown and inductor peak current
limit. The STLED25 is packaged in a 12-bump
CSP (1.4 x 1.8 mm, 0.5 mm height).

The STLED25 is a fixed frequency, high efficiency,
boost DC-DC converter with five parallel high side
current sources. It is capable of providing 125 mA
of total current with a maximum voltage of 7.5 V
on each channel. Each current source supports
single or dual LED connection. The output voltage
of the step-up converter is automatically set at
100 mV above the highest voltage required on
any driver, to guarantee proper operation of the
linear current sources. The device implements a
self-test feature to detect failure of any of the
LEDs and to disable the related channel. The
failure status is reset as soon the IC is disabled.
This mode of failure detection allows the device to

Table 1. Device summary

Order code Package Packaging

STLED25JR Flip-Chip12 Tape and reel

May 2012 Doc ID 022323 Rev 3 1/30

This is information on a product in full production.

www.st.com

30

Contents STLED25

Contents

1 Application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5 Typical application performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.1 Quiescent current consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.2 Switching frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.3 Continuous output current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.4 Efficiency at 100 mA I

5.5 Efficiency at 75 mA I

5.6 Efficiency at 50 mA I

5.7 Absolute channel accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.8 Current matching between LED strings . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.9 PWM dimming linearity 0.39 - 10% . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5.10 PWM dimming linearity 10 - 100% . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5.11 Inductor peak current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

5.12 Maximum continues output current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

OUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

OUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

OUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6 Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

6.1 Boost DC-DC converter operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

6.2 Current setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

6.3 EN13 and EN45 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

6.4 Modes of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6.5 Undervoltage lockout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6.6 Overtemperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6.7 Open LED protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6.8 Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6.9 Short LED protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2/30 Doc ID 022323 Rev 3

STLED25 Contents

7 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

7.1 External passive components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

7.1.1 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

7.1.2 Input and output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

7.2 Recommended PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

8 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Doc ID 022323 Rev 3 3/30

Application schematic STLED25

1 Application schematic

Figure 1. STLED25 application schematic

Table 2. Typical external components

Component Manufacturer Part number Value Size

C

IN

C

OUT

L Samsung CIG21K4R7SCE 4.7 µH 0805

R

SET

1. For 20 mA per branch.

Murata GRM155R60J155M 1.5 µF 0402

Murata GRM219R61A106ME47 10 µF 0805

(1)

25 k

0402

Note: All the above components refer to a typical application. Operation of the device is not limited

to the choice of these external components.

4/30 Doc ID 022323 Rev 3

STLED25 Application schematic

Figure 2. Functional block diagram

Doc ID 022323 Rev 3 5/30

Pin configuration STLED25

2 Pin configuration

Figure 3. Pin configuration (top view)

VIN ISET D1

EN13 EN45 D2

GND D5 D3

SW VOUT D4

AM09921v1

Table 3. Pin description

Pin name Pin number Description

VIN A1 Supply from battery

ISET A2

D1 A3 String 1 controlled by EN13

EN13 B1 Positive polarity. EN13 & 45 Low = IC shutdown

EN45 B2 Positive polarity. EN13 & EN45 Low = IC shutdown

D2 B3 String 2 controlled by EN13

GND C1 Power ground and IC ground

D5 C2 String 5 controlled by EN45

D3 C3 String 3 controlled by EN13

SW D1 Inductor connection to internal switch

VOUT D2 DC-DC output to V

D4 D3 String 4 controlled by EN45

Resistor to GND from 1.28 V (typ.) internal reference: 390x current
multiplier

capacitor

OUT

6/30 Doc ID 022323 Rev 3

STLED25 Maximum ratings

3 Maximum ratings

Table 4. Absolute maximum ratings

Symbol Parameter Value Unit

VIN Supply voltage -0.3 to +6 V

SW Switching node -0.3 to + 11 V

VOUT Output voltage -0.3 to +10 V

D1-D5 LED strings -0.3 to +10 V

EN13, EN45 Signal pins -0.3 to VIN V

ISET Current setting -0.3 V to 2 V

Machine model ± 200

ESD

Charged device model ± 500

VHuman body model ± 2000

T

T

AMB

T

J

STG

Operating ambient temperature -30 to 85 °C

Maximum operating junction temperature +150 °C

Storage temperature -65 to 150 °C

Table 5. Thermal data

Symbol Parameter Value Unit

R

THJA

1. This parameter corresponds to a 4-layer PCB board with 1 inch² of cooling area.

Junction to ambient thermal resistance

(1)

62 °C/W

Doc ID 022323 Rev 3 7/30

Electrical characteristics STLED25

4 Electrical characteristics

- 30 °C < TA < 85 °C, VIN = 3.7 V; V
= 25 °C, unless otherwise specified.

T

A

Table 6. Electrical characteristics

= 7.5 V, EN13 = EN45 = VIN, typical values are at

OUT

Symbol Parameter Test conditions Min. Typ. Max. Unit

General section

V

IN

Operating input voltage 2.3 3.7 5.5 V

Iq Shutdown mode EN13 = EN45 = 0 0.5 2 µA

V

rising 1.9 2.0

V

ν

V

OVP

UVLO

f

SW

I

OUT

I

PK

ν

DC-DC

OVP

HYST

Undervoltage lockout
threshold

Switching frequency 2.25 2.5 2.75 MHz

Continuous output current

Inductor peak current 550 650 mA

OUT

(1)

= 6.2 V;

Application efficiency
(V

= 3.7 V; V

IN

see application schematic)

DC-DC converter efficiency I

Overvoltage protection 8.8 9.05 9.3 V

Overvoltage protection
hysteresis

IN

VIN falling 1.7 1.8

(1)

V

= 2.5 V, V

IN

I

= 50 mA 84

OUT

I

= 75 mA 86

OUT

I

= 100 mA 86

OUT

= 100 mA 88

OUT

= 6.2 V 125 mA

OUT

250 mV

V

%

T

SHDN

Hysteresis 20 °C

LEDs current

Thermal shutdown 150 °C

I

D1-D5

V

SCP

I

LED

I

SET

V

CSH

Current matching -5.5 +5.5 %

Short-circuit protection on
LEDs

Absolute channel accuracy

Voltage reference R

Current mirror I

Measured on the Dx pins 1.28 V

5 mA < I

= 2.5 V to 5.5 V

V

IN

2.5 mA < I
= 2.5 V to 5.5 V

V

IN

SET

/ I

LED

< 25 mA,

LED

< 5 mA,

LED

= 200 k to 15 k 1.28 V

SET

Current source headroom
voltage

8/30 Doc ID 022323 Rev 3

-7.5 +7.5 %

-10 10 %

390 A/A

135 mV

STLED25 Electrical characteristics

Table 6. Electrical characteristics (continued)

Symbol Parameter Test conditions Min. Typ. Max. Unit

I

RIPPLE

PWM

I

LED_LEAK

I

LED_MAX

LED peak-to-peak current

(1) (2)

ripple

LIN

PWM linearity

(1) (2)

LED driver leakage in OFF
state

LED driver max current 25 mA

Line_tr Line transient response

D

f

DIM

DIM

PWM dimming frequency 100 800 Hz

Duty cycle of PWM dimming 0.39 100 %

Logic inputs

R

I

V

V

LK-I

EN

IL

IH

Internal pull-down resistor 100 kΩ

EN low-level input voltage

EN high-level input voltage

EN input leakage current

(1)

VIN = 2.5 V; I
all channels,
EN13

PWM

= 2.5 V; I

V

IN

all channels,
EN13

PWM

1/255 PWM, 300 Hz, 20 mA
on all drivers, V

LED

= EN45

LED

= EN45

IN

= 20 mA at

PWM

= 20 mA at

PWM

= 2.5 V

(3)

500 µA

4000

10 %

25/255 PWM, 300 Hz, 20
mA on all drivers, VIN = 2.5 V

(3)

= 7.5 V 0.5 µA

V

OUT

2%

VINTR=+/-350mV,10µs step 30 %

V

= 2.7 V to 4.5 V 0.68

IN

= 2.3 V to 5.5 V 0.55

V

IN

V

= 2.7 V to 4.5 V 1.07

IN

= 2.3 V to 5.5 V 1.14

V

IN

= V

V

EN

internal pulldowns

= 4.2 V, 100 k

IN

42 µA

V

V

Power switches

P-channel on resistance 880

R

DSON

I

LKG-LX

1. Not tested in production

2. 10% value reduction at V

3. The PWM linearity is measured on the mean value of the output current in PWM mode in the 100 ms window. The
frequency of the PWM is 300 Hz

N-channel on resistance 450

LX leakage current VIN=VLX=4.8V; VEN=0 1 µA

= 2.3 V

IN

Doc ID 022323 Rev 3 9/30

mΩ