LM3565

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SNVS957 – JANUARY 2013

APPLICATION INFORMATION

Torch or Assist (Continuous Current) Operation

There are two different continuous current modes on the LM3565: Torch and Assist.

Torch Mode is enabled through the use of the dedicated Torch pin. The Torch pin functionality can be enabled

and disabled by setting the value of the ETEN bit in the TX-Control Register (Address 0x03). ETEN = '1' allows

an external Torch while ETEN = '0' does not.

The primary method to enable Assist Mode is by setting the Output Mode bits (OM1 and OM0) to '10' and setting

the Output Enable bit (OEN) to a '1' in the Control Register (0x07). Assist Mode will remain active in I2C-

compatible Mode until the OEM bit is set to '0'.

The secondary Assist Mode enabling method involves using the Strobe pin. By setting the SEN bit in the Stobe

Signaling Register (Address 0x06) to a '1', then setting the Output Mode bits (OM1 and OM0) to '10' and setting

the Output Enable bit (OEN) to a '1' in the Control Register (0x07), the LM3565 will be configured to enable

Assist Mode upon the Strobe pin transitioning state from low to high. In this configuration, Assist Mode will

remain active until the OEN bit is set to '0'. Transitioning the Strobe pin from high to low does not automatically

clear the OEN. In Assist Mode, the Strobe Signal Usage bit (SSU in Strobe Signaling Register 0x06) is ignored,

and the Strobe pin is always set to be edge sensitive.

The LM3565 can drive two LEDs at continuous current levels of 60 mA or 90 mA. The current is set in the

Current Set Register utilizing the AS0 bit (Address 0x02, AS0). Writing a '0' (default) sets the assist current to 60

mA while writing a '1' sets the assist current to 90 mA.

In Torch or Assist Mode, the LED current is ramped up to 90 mA in 30 mA steps at 20 µs intervals, then reduced

to 60 mA if the assist target current is set to 60 mA. The assist current is terminated in one step.

Flash (Pulsed Current) Operation

A flash event using the LM3565 can be initiated though the I2C-compatible control interface, and through the use

of the Strobe pin.

When using the I2C-compatible Control Mode, a flash event is initiated when the Output Mode bits (OM1 and

OM0) are set to '11' and the Output Enable bit (OEN) is set to a '1' in the Control Register (0x07). In I2C-

compatible Mode, the flash event will remain active as long as the OEN bit is set to a '1' and will terminate upon

a time-out event. The safety timer duration can be set in 2 ms intervals ranging from 2 ms to 512 ms by writing

the desired value to the FT7-FT0 bits in the Timer Register (Address 0x05, with the default timer set to 72

msec.).

The Strobe pin provides added system flexibility in that it allows an additional external device (Camera Module,

GPU etc.) to trigger a flash event. To initiate a Strobe event in I2C-compatible Control Mode, the Strobe Enable

(SEN) bit in the Strobe Signaling Register (0x06) must first be set to a '1', and the Output Enable (OEN) bits and

Output Mode bits (OM1 and OM0) in the Control Register (Address 0x07) must be set to '1's.

Following the setting of the SEN and OEN bits, the user must choose to have an edge-sensitive or level-sensitive

strobe event. Writing a '1' to the Strobe Signal Usage (SSU) bit in the Control Register (Address 0x06), the

LM3565 will be configured to be level sensitive, while writing a '0' configures the part to be edge-sensitive. In

both cases, the strobe flash event is started upon the Strobe pin being driven high.

In an edge-sensitive event, the flash duration will stay active until the flash duration timer lapses regardless of

the state of the Strobe pin. If a level-sensitive strobe is used, the flash event will remain active as long as the

Strobe pin is held high and as long as the flash duration time has not lapsed.

In Flash Mode, the LED current is ramped up and down in 30 mA steps at 20 µs intervals.

At the end of a flash event, whether initiated through the Control Register or Strobe pin, the LM3565 will force

the OEN bit to a '0' and will place the LM3565 back into the Standby state.

Copyright © 2013, Texas Instruments Incorporated

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