ST STCF07 User Manual

High power buck-boost white LED driver

Features

■ Buck-boost DC-DC converter

■ Drives one power LED up to 1 A in flash mode

■ Drives one power LED up to 800 mA in

continuous mode

■ LED temperature protection

■ Output current control

■ 1.8 MHz (typ.) fixed frequency PWM

■ Synchronous rectification

■ High efficiency across the total input voltage

range

■ Operational modes:

– Shutdown mode
– High current mode: up to 1 A
– Low current mode: from 20 mA

■ Adjustable current in both modes

■ Peak inductor limited to 2.3 A (typ.)

■ LED disconnected from the battery in

shutdown mode

■ NTC LED temperature protection

■ Overvoltage protection: 5.3 V

■ Short-circuit protection

■ Overtemperature protection

■ ULVLO function

■ 1 µA max shutdown current

■ QFN16 (4 x 4 x 1 mm) 16 leads

Applications

STCF07

QFN16 (4 x 4 mm)

Description

The STCF07 is a dedicated, size-optimized
solution for driving a power LED. The device is a
buck-boost converter which guarantees proper
LED current control over all possible battery
voltage and LED forward voltage conditions. The
output current control ensures good current
regulation over the forward voltage spread
characteristics of high-brightness LEDs. The
device includes various functions to protect the
chip and the power LEDs. These include soft-start
control as well as detection and protection of chip
overtemperature and shorted LEDs. An optional
external NTC is supported to protect the LEDs
against overheating. It is possible to separately
program the current intensity in HIGH and LOW
mode using the SEL pin. The device is housed in
a 16-lead QFN16 (4 x 4 mm) package with a
height less than 1 mm.

■ Camera flash for mobile phones

■ Power supply for high power LEDs

Table 1. Device summary

Order code Package Packaging

STCF07PNR QFN16 (4 x 4 mm) Tape and reel

April 2011 Doc ID 16757 Rev 2 1/26

www.st.com

26

Contents STCF07

Contents

1 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

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

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

4 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

6 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

7 Logic pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

7.1 CSEL pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

7.2 FAULT pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

7.3 ENABLE pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

8 Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

8.1 Buck-boost converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

8.2 High current mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

8.3 Low current mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

8.4 Shutdown mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

8.5 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

8.6 STCF07 protection features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8.6.1 Peak current and short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . 13

8.6.2 Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8.6.3 Thermal shutdown protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8.6.4 Sensing of LED temperature with the NTC resistor . . . . . . . . . . . . . . . . 13

8.6.5 Undervoltage lockout function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

9 PCB design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9.1 PCB design rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9.2 PCB design of the demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . 16

9.3 Schematic of the demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2/26 Doc ID 16757 Rev 2

STCF07 Contents

10 Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

11 External component selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

11.1 Input and output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

11.2 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

11.3 LED selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

11.4 RHC selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

11.5 RLC selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

11.6 NTC and RX resistor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

12 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

13 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Doc ID 16757 Rev 2 3/26

Block diagram STCF07

1 Block diagram

Figure 1. STCF07 block diagram

VLX2VLX1AVLX1B

VLX2VLX1AVLX1B

CURRENT

PVBAT

PVBAT

VBAT

VBAT

GND

GND

ENABLE

ENABLE

CSEL

CSEL

FAULT

FAULT

OVER

OVER
TEMP

TEMP

CURRENT

PROTECTION

PROTECTION

LOGIC

LOGIC

MX

MX

VOUT

VOUT

FB1

FB1

BANDGAP

BANDGAP

REF

REF

SOFT

SOFT

START

START

REF

REF

DRIVER

DRIVER

OSC

OSC

NTC

NTC

CONTROL

CONTROL

PNGD RX NTC

PNGD RX NTC

FB2

FB2

FB2S

FB2S

4/26 Doc ID 16757 Rev 2

STCF07 Pin configuration

2 Pin configuration

Figure 2. STCF07 pin connections (top view)

Table 2. STCF07 pin description

Pin n° Symbol Description

1 VLX2 Inductor VLX2 connection

8RXR

resistor connection

X

2 NTC NTC resistor connection

3 VOUT Output voltage

4 FB1 Feedback pin [I

5FB2R

bypass

TR

6 FB2S Feedback pin [I

*(RHC+RLC)]

LED

LED*RHC

]

14 GND Signal ground

13 CSEL Current selection

7 EN Enable

16 FAULT Diagnostic

9 PVBAT Power supply voltage

10 VBAT Supply voltage

11 VLX1A Inductor VLX1 connection

12 VLX1B Inductor VLX1 connection

15 PGND Power ground

Exposed pad PGND

To be connected to the PCB ground plane for optimal electrical and
thermal performance

Doc ID 16757 Rev 2 5/26

Maximum ratings STCF07

3 Maximum ratings

Table 3. Absolute maximum ratings

Symbol Parameter Value Unit

VBAT Signal supply voltage -0.3 to 6 V

PVBAT Power supply voltage -0.3 to 6 V

VLX1A, VLX1B Inductor connection 1 -0.3 to V

VLX2 Inductor connection 2 -0.3 to V

+0.3 V

I

+0.3 V

I

VOUT Output voltage -0.3 to 6 V

FB1, FB2, FB2S Feedback and sense voltage -0.3 to 3 V

R

X

CSEL Current selection -0.3 to V

EN Enable -0.3 to V

FAULT Diagnostic -0.3 to V

Connection for reference resistor -0.3 to 3 V

+0.3 V

I

+0.3 V

I

+0.3 V

I

NTC Connection for LED temperature sensing -0.3 to 3 V

ESD Human body model ±2kV

P

T

T

STG

TOT

OP

T

J

Continuous power dissipation (at TA = 70 °C) 800 mW

Operating junction temperature range -40 to 85 °C

Junction temperature -40 to 150 °C

Storage temperature range -65 to 150 °C

Note: Absolute maximum ratings are those values beyond which damage to the device may occur.

Functional operation under these condition is not implied.

Table 4. Thermal data

Symbol Parameter Value Unit

(1)

R

thJA

1. Junction-to-ambient thermal resistance in JEDEC still air chamber. Thermal test board JESD51-7 (leaded surface mount
packages).

6/26 Doc ID 16757 Rev 2

Thermal resistance junction-ambient 31 °C/W

STCF07 Application information

4 Application information

Figure 3. Application schematic diagram

L

L

V

V

IN

IN

C

C

IN

IN

VLX1 VLX1

VLX1 VLX1

PVBAT

PVBAT

VBAT

VBAT

ENABLE

ENABLE

CSEL

CSEL

FAULT

FAULT

GND PGND

GND PGND

RX

RX

VLX2

VLX2

VOUT

VOUT

FB1

FB1

FB2

FB2

FB2S

FB2S

NTC

NTC

NTC

NTC

LED

LED

R

R

LC

LC

R

R

HC

HC

C

C

OUT

OUT

R

R

X

X

Optional components

Optional components

Note: Represents a typical application schematic for an output current of 800 mA (max) in

continuous mode operation. For pulse/flash mode operation it is possible to increase the
maximum output current up to 1 A. If the battery voltage is higher than 3.1 V, the chip is
capable of delivering the maximum output current of up to 1 A in continuos mode.

Table 5. List of external components

Component Manufacturer Part number Value Size

C

NTC MURATA NCP18WF104J03RB 100 kΩ 0805

1. For 800 mA output current performance.

2. For 1000 mA output current performance.

Welwyn LR1206-R20FI

R

R

C

HC

LC

IN

OUT

KOA SR732BTTDR160F

Tyco Electronics CRL1220T1R8J 1.8 Ω 0805

TDK C1608X5R0J106MT 10 µF 0603

TDK C1608X5R0J475M 4.7 µF 0603

VLF4014ST-2R2M1R9

LTDK

VLF5014S-2R2M2R3

R

X

Tyco Electronics 1-1879132-9 15 kΩ 0402

LED Luxeon LXHL_PW09

(1)

(2)

(2)

(1)

0.2 Ω 1206

0.16 Ω 1206

2.2 µH / 1.4 A 3.5x3.8x1.4 mm

2.2 µH / 2.3 A 4.6x4.8x1.4 mm

Note: The above-listed external components refer to a typical application. Operation of the

STCF07 is not limited to the use of these components.

Doc ID 16757 Rev 2 7/26

Electrical characteristics STCF07

5 Electrical characteristics

TA = 25 °C, VI = 3.6 V, 2 x CI = 10 µF, CO = 1 µF, L = 2.2 µH, RHC = 0.22 Ω, RLC = 1.8 Ω,
R

= 15 kΩ

X

Table 6. Electrical characteristics

Symbol Parameter Test conditions Min. Typ. Max. Unit

V

I

UVLO Undervoltage lockout V

V

PW_ONRESET

I

O

V

OUT

ILIM Inductor peak current

Input voltage supply 2.7 5.5 V

= 2.7 V 2.2 V

I

Power ON reset threshold VI rising 2.3 V

Output current - high current
level

Output current - high current
level

Output current - low current
level

CSEL = VI; VI = 2.7 V to 5.5 V;
R

= 0.16 Ω, P

HC

CSEL = V
R

HC

; VI = 3.2 V to 5.5 V;

I

= 0.16 Ω, P

CSEL = GND; V
R

+ R

LC

~ 2 Ω

HC

= 3.4 W

OUT

= 4 W

OUT

= 3.3 V to 5.5 V;

I

1000

1000

20

Regulated voltage range 2.5 5.3 V

V

= 2.7 V, V

I

operation

shorted during

OUT

2.3 A

FB1 Feedback voltage Low current (CSEL = 0 V) 152 160 168 mV

FB2 Feedback voltage High current (CSEL = VI) 152 160 168 mV

= GND

)

I

90 mΩ

1.8 mA

00.4

1.4 3

R

ON_

FB1-FB2 ON resistance

Quiescent current in
shutdown mode

I

Q

Quiescent current in high
current mode

f

s

Frequency VI = 2.7 V 1.8 MHz

n Efficiency V

OVP

OV

HYST

Output overvoltage
protection

Overvoltage hysteresis VI = 5.5 V, no load 0.3 V

OTP Overvoltage protection V

OT

V

V

NTC

HYST

NTC

RX

LEAK

V

IL

V

IH

Overvoltage hysteresis VI = 5.5 V 20 °C

NTC voltage reference VI = 2.7 V to 5.5 V 1.8 V

NTC voltage threshold I

RX-NTC switch OFF leakage

Input logic signal level CSEL,
EN

High current (CSEL = V
IO = 800 mA

EN = GND 1 µA

EN = V

5.5 V; R

; CSEL = VI; VI = 3.3 V to

I

= 0.22 Ω

HC

= 3.2 to 4.2 V, IO = 800 mA 85 %

I

VI = 5.5 V, no load 5.5 V

= 5.5 V 140 °C

I

= 1 mA Max 1.2 V

NTC

Shutdown mode,

= 2 V - V

V

NTC

= 2.7 V to 5.5 V

V

I

RX

mA

1µA

V

8/26 Doc ID 16757 Rev 2