STCF06TBR Datasheet STCF06TBR | P13-P15

STCF06 Detailed description

Doc ID 14549 Rev 3 13/35

7 Detailed description

7.1 Introduction

The STCF06 is a buck-boost converter, dedicated to power and control the current of a

power white LED in a camera cell phone. The device operates at a typical constant

switching frequency of 1.8 MHz. It regulates the LED current up to 1.5 A and supports LED

with forward voltage ranging from 2.5 V to 5.0 V. The input voltage supply range from 2.7 V

to 5.5 V allows operation from a single cell Lithium-Ion battery. The I²C bus is used to control

the device operation and for diagnostic purposes. The current in torch mode is adjustable up

to 370 mA. Flash mode current is adjustable up to 1500mA for an input voltage higher than

3.5 V, 1300 mA for an input voltage of 3.0 V at least and 1000 mA when the input voltage is

2.7 V. The Aux LED current can be adjusted from 0 to 20 mA. The device uses an external

NTC resistor to sense the temperature of the white LED. These two last functions may not

be needed in all applications, and in these cases the relevant external components can be

omitted.

7.2 Buck-boost converter

The regulation of the PWM controller is done by sensing the current of the LED through

external sensing resistors (R

and R

, see application schematic). Depending on the

forward voltage of the flash LED, the device automatically can change the operation mode

between buck (step down) and boost (step up) mode.

Three cases can occur: Boost region (V

> V

BAT

): this configuration is used in most of the

cases, as the output voltage V

= V

fLED

+ I

LED

x R

is higher than V

BAT

; Buck region (V

BAT

); Buck / Boost region (V

~ V

BAT

7.3 Logic pin description

7.3.1 SCL, SDA pins

These are the standard clock and data pins as defined in the I²C bus specification. External

pull-up is required according to I²C bus specifications. The recommended maximum voltage

of these signals should be 3.0 V.

7.3.2 TRIG pin

This input pin is internally AND-ed with the TRIG_EN bit to generate the internal signal that

activates the flash operation. This gives to the user the possibility to accurately control the

flash duration using a dedicated pin, avoiding the I²C bus latencies (hard-triggering). No

internal pull-up nor pull-down is provided.

7.3.3 ATN pin

This output pin (open-drain, active LOW) is provided to better manage the information

transfer from the STCF06 to the microprocessor. Because of the limitations of a single

master I²C bus configuration, the microprocessor should regularly poll the STCF06 to verify

if certain operations have been completed, or to check diagnostic information. Alternatively,

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Detailed description STCF06

14/35 Doc ID 14549 Rev 3

the microprocessor can use the ATN pin to be advised that new data are available in the

STAT_REG, thus avoiding continuous polling. Then the information can be read in the

STAT_REG by a read operation via I²C that, besides, automatically resets the ATN pin. The

STAT_REG bits affecting the ATN pin status are mapped in Ta bl e 1 5 . No internal pull-up is

provided.

7.3.4 ADD pin

With this pin it is possible to select one of the 4 possible I²C slave addresses. No internal

pull-up nor pull-down is provided. The pin has to be connected to either GND, V

,SCL or

SDA to select the desired I²C slave address (see Tabl e 7)

7.3.5 TMSK pin

This pin can be used to implement the TX masking function. This function has effect only for

flash current settings higher than 370 mA (bit FDIM=7hex). Under this condition, when this

pin is pulled high by the microprocessor, the current flowing in the LED is forced at 370 mA

typ. No internal pull-up or pull-down is provided; to be externally wired to GND if TX masking

function is not used. The value corresponds to R

resistor 0.15 ohm.

7.4 Power-on reset

This mode is initiated by applying a supply voltage above the V

PW_ON RESET

threshold

value. An internal timing (~1 µs) defines the duration of this status. The logic blocks are

powered, but the device doesn't respond to any input. The registers are reset to their default

values, the ATN and SDA pins are in high-Z, and the I²C slave address is internally set by

reading the ADD pin configuration. After the internally defined time has elapsed, the

STCF06 automatically enters the Stand-by mode.

7.5 Shutdown, shutdown with NTC

In this mode only the I²C interface is alive, accepting I²C commands and register settings.

The device enters this mode: automatically from power-on reset status; by resetting the

PWR_ON bit from other operation modes. Power consumption is at the minimum (1 µA max)

if NTC is not activated (NTC_ON=0). If PWR_ON and NTC_ON is set, the T1 is switched

ON (see Figure 1), allowing the microprocessor to measure the LED temperature through its

A/D converter.

Table 7. Address table

ADD pin A7 A6 A5 A4 A3 A2 A1 A0

GND0110000R/W

VBAT0110001R/W

SDA0110010R/W

SCL0110011R/W

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STCF06 Detailed description

Doc ID 14549 Rev 3 15/35

7.6 Ready mode

In this mode all internal blocks are turned ON, but the DC-DC converter is disabled and the

White LED is disconnected. The NTC circuit can be activated to monitor the temperature of

the LED and I²C commands and register settings are allowed to be executed immediately.

Only in this mode the auxiliary LED is operational and can be turned ON and set at the

desired brightness using the AUX REGISTER. The device enters this mode: from Stand-by

by setting the PWR_ON bit; from flash operation by resetting the TRIG pin or the TRIG_EN

bit or automatically from flash operation when the time counter reaches zero; from torch

operation by resetting the TCH_ON bit. The device automatically enters this mode also

when an overload or an abnormal condition has been detected during flash or torch

operation (Table 16: Status register details:).

7.7 Single or multiple flash using external (microprocessor)

temporization

To avoid the I²C bus time latency, it is recommended to use the dedicated TRIG pin to define

the flash duration (hard-triggering). The TRIG_EN bit of CMD_REG should be set before

starting each flash operation, because it could have been reset automatically in the previous

flash operation. The flash duration is determined by the pulse length that drives the TRIG

pin. As soon as the flash is activated, the system needs typically 1.2 ms to ramp up the

output current on the Power LED. The internal time counter will time-out flash operation and

keep the LED dissipated energy within safe limits in case of Software deadlock; FTIM

by strobing the TRIG pin. Time out counter will cumulate every flash on-time until the

defined time out is reached unless it is reloaded by updating the CMD_REG. After a single

or multiple flash operations are timed-out, the device automatically goes into Ready mode

by resetting the TRIG_EN bit, and also resets the F_RUN bit. The ATN pin is pulled down to

inform the microprocessor that the STAT_REG has been updated.

7.8 External (microprocessor) temporization using TRIG_EN bit

Even if it is possible, it is not recommended to use the TRIG_EN bit to start and stop the

flash operation, because of I²C bus latencies: this would result in inaccurate flash timing.

Nevertheless, if this operation mode is chosen, the TRIG pin has to be kept High (logic level

or wired to V

BAT

), leaving the whole flash control to the I²C bus. Also in this operation mode

the Time Counter will Time-out flash operation and keep the energy dissipated by the LED

within safe limits in case of SW deadlock.

7.9 Single flash using internal temporization

Flash triggering can be obtained either by TRIG pin (hard-triggering) or by I²C commands

(soft-triggering). The first solution is recommended for an accurate start time, while the

second is less accurate because of the I²C bus time latency. Stop time is defined by the

STCF06 internal temporization and its accuracy is determined by the internal oscillator. For

hard-triggering, it is necessary to set the TRIG_EN bit in advance. For soft-triggering, the

TRIG pin has to be kept High (logic level or wired to V

BAT

) and the flash can be started by

setting the FTIM and the TRIG_EN through I²C (both are located in the CMD REG). There is

a delay time between the moment the flash is triggered and when it appears. This delay is

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STCF06TBR

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LED Lighting Drivers 1.5A WHITE LED DRVR

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