ST STCF02 User Manual
General features
■ Buck-boost DC/DC Converter
■ Drives one power white led:
up to 600mA between 2.7 to 4.5V
■ 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
- Shutdown mode with NTC
- Flash mode up to 600 mA
- Medium flash mode
- Torch mode: up to 250 mA
■ Adjustable current in all three modes
■ LED disconnected from the battery in
shutdown mode
■ Programmable safety shutdown in flash mode
■ LED short and open circuit protection
■ Overvoltage protection
■ < 1µA Shutdown current
■ QFN20 4mm x 4 mm package
Applications
■ Cell phone and smart phones
■ Camera flashes/strobes
■ PDAS and digital still cameras
STCF02
High power white led driver
QFN20 (4mm x 4mm)
Description
The STCF02 is a high efficiency power supply
solution to drive a single flash LED in camera
phone, PDAs and other hand-held devices. It is a
buck-boost converter that guarantees a proper
LED current control over the battery voltage
(particularly in the case, when the output voltage
is lower than the input voltage); the output current
control ensures a good current regulation over the
forward voltage spread characteristics of the
Flash LED.
Three logic input signals can select 5 modes of
operation: Shutdown mode (quiescent current
less than 1µA typ), Shutdown mode with NTC
active, Torch mode (drives the LED up to 250mA),
Flash mode (up to 600mA), and Medium flash
mode (reduces the flash current).
This highly efficient converter is able to accept
input current from the battery (lower than 1.5A),
while limiting the peak inductor current to 2.3A
(typ). Other features include Soft start control,
thermal shutdown, short circuit protection,
overvoltage protection, and LED temperature
protection. An alternative to LED temperature
protection is that a safety flash time-out feature
can be implemented instead. This device is
available in a QFN20, 4mm x 4mm, no-lead
package (height is less than 1mm).
Order code
Part number Package Packaging
STCF02PNR QFN20 (4x4 mm) 4500 parts per reel
February 2007 Rev. 6 1/19
www.st.com
19
Contents STCF02
Contents
1 Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Pin connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4 Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6 Detailed operating description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.2 Buck-Boost converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.3 Flash mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.4 Medium flash mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.5 Torch mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.6 Shutdown mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.7 Soft start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.8 LED Failure Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.9 Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.10 Thermal shutdown protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.11 Sensing of LED temperature by NTC resistor . . . . . . . . . . . . . . . . . . . . . . . . 14
6.12 Safety shutdown in flash mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2/19
STCF02 Application
1 Application
Figure 1. Application circuit
Table 1. External components
Symbol Parameter Min. Typ. Max. Unit
R
FLASH
R
TORCH
R
C
C
NTC Negative thermistor - NCP18WF104J03RB - Thick film type 100 kΩ
C
COMP
R
C1 Ceramic Capacitor 47 pF
Sensing flash current resistor - thick film type (0805) 0.27 Ω
Sensing torch current resistor - thick film type (0603) 6.2 Ω
Setting resistor for middle flash mode - thick film type (0402) 8200 Ω
MF
Two Input filtering capacitor TDK C1608X5R0J106MT - Ceramic
I
type (0603) 6.3V
Output capacitance - Ceramic type 0603 6.3V 4.7 µF
O
L TDKVLF5014A-4R7
Compensation capacitor - 0402 100 820 pF
Reference resistor - 0402 15 kΩ
X
INDUCTANCE 4.7 µH
DCR 0.12 Ω
10 2x10 µF
Note: - The external components proposal should be considered as a design reference guide. The
performances mentioned in the electrical characteristics table are not guaranteed for all the
possible electrical parameters of the components included in this list. On the other hand the
operation of STCF02 is not limited with the use of the external components listed above.
- The C
is optional and may be used if the error amplifier bandwidth (which by default is
COMP
set to 2 KHz) has to be decreased because of an unstable driver function. Unstable operation
could be caused by using different values of inductor and output capacitor then recommended.
3/19
Pin connections STCF02
2 Pin connections
Figure 2. Pin configuration (bottom view)
Table 2. Pin description
Pln N° Symbol Name and function Note
External coil is connected between this pin and VLX1. It should be
1 VLX2 Inductor connection
2 RX Rx Resistor connection
V
3
4 NTC NTC Resistor connection
5FB1
6RTBY
7FB2
8, 10 GND Signal ground
9COM1
11 COM2
12 VBAT Supply voltage Supply pin of the device.
13 PVBAT Power supply voltage Power supply pin of the device.
14 VLX1A
15 VLX1B
16 EN3 Enable Pin 3
17 EN2 Enable Pin 2
Output voltage Anode of the LED is connected to this pin.
O
Feedback pin for torch
mode
TORC H
Bypass
R
Feedback pin for flash
mode
Compensation
connection
Compensation
connection
Inductor connection
placed as close as possible to the device in order to minimize
resistance which cause losses.
Rx resistor is connected between this pin and ground to set LED over
temperature threshold.
This pin is used for the LED temperature sensing using an external
NTC resistor.
This pin is used for current sensing in Torch mode – Cathode of the
Flash LED and RTorch resistor are connected to this pin.
This pin is used to short-circuit the R
MIDDLE FLASH MODE.
This pin is used to sense the voltage across R
directly connected to the non-grounded terminal of R
This is the signal ground pin related to digital and analog signals and
must be connected as close as possible to the sensing resistor.
Optional external compensation should be connected to these pins.
Optional external compensation should be connected to these pins.
External coil is connected between these pins and VLX2. They should
be placed as close as possible to the device in order to minimize
resistance which causes losses. It is mandatory to connect VLX1A
and VLX1B together.
Digital input that allows selection of the operational modes of the
device (refer to truth table).
Digital input that allows selection of the operational modes of the
device (refer to truth table).
during FLASH and
TORCH
FLASH
. It must be
.
FLASH
4/19
STCF02 Pin connections
Pln N° Symbol Name and function Note
18 PGND Power ground
19 RMFL
20 EN1 Enable Pin 1
Exp-
pad
PGND Power ground
Middle flash resistor
connection
Figure 3. Block diagram
Power ground pin for power analog circuit. To be connected to the
PCB ground plane.
This pin is used for the current setting in Middle Flash Mode – RMF
resistor is connected to this pin.
Digital input that allow selecting the operational modes of the device
(refer to truth table).
To be connected to the PCB Ground Plane for optimal electrical and
thermal performance.
5/19
Maximum ratings STCF02
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
EN1,2,3 Enable input -0.3 to 6 V
V
O
VLX1A-VLX1B Inductor connection 1
VLX2 Inductor connection 2
FB1 Feedback for torch current -0.3 to 3 V
FB2 Feedback for flash current -0.3 to 3 V
RTBY MOS Switch connection -0.3 to 3 V
RX Connection for reference resistor -0.3 to 3 V
RMFL Connection for setting resistor for middle flash -0.3 to 6 V
NTC LED temperature sensing connection -0.3 to 6 V
COM1,COM2 Compensation connection -0.3 to 3 V
T
OP
T
STG
V
ESD
1. STCF02 is guaranteed to meet specification from 0°C to 70°C – specifications over the -40°C to 85°C operating
temperature range are assured by design, characterization and correlation with statistical process control.
Output voltage -0.3 to 6 V
+ 0.3
I
O
+ 0.3
V
V
Ambient operating temperature
(1)
-0.3 to V
-0.3 to V
-40 to + 85 °C
Storage temperature range -65 to + 150 °C
ESD rating 2 KV
Table 4. Thermal data
Symbol Parameter Value Unit
R
thJA
(*) Typical Application on a two layer board.
Thermal resistance junction-ambient (*) 59 °C/W
6/19
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