SCL

SDA

data

change

allowed

data

valid

data

change

allowed

data

valid

data

change

allowed

LM3642

SNVS891H – SEPTEMBER 2012 – REVISED SEPTEMBER 2015

www.ti.com

Device Functional Modes (continued)

Table 1. Status of Mode Bits

MODE CHANGE REQUIRED

STATUS OF MODE BITS IN THE ENABLE REGISTER AFTER A FLASH

Using Level Triggered STROBE to Flash

Mode bits are cleared after a single flash. To reflash, 0x23 will have to be written

to 0x0A.

7.4.4 Torch Mode

In Torch Mode, the current source (LED) is programmed via the Current Control Register. Torch Mode is

activated by the Enable Register and/or by Enabling the part in TX/Torch pin configuration. Once the Torch Mode

is enabled the current source will ramp up to the programmed Torch current level. The Ramp-Up and Ramp-

Down times are independently adjustable via the Torch Ramp Register. Torch Mode is not affected by Flash

Timeout. In the LM3642, the programmable torch current ranges from 48.4 mA to 375 mA. With the LM3642LT

option, the programmable torch current ranges from 24 mA to 187 mA.

7.4.5 Indicator Mode

This mode is activated by the Enable Register. The LM3642 can be programmed to a current level that is 1/8th

the torch current value in the Current Control Register. LM3642LT has only one setting of indicator current at 5

mA.

7.5 Programming

7.5.1 I2C-Compatible Interface

7.5.1.1 Data Validity

The data on SDA line must be stable during the HIGH period of the clock signal (SCL). In other words, state of

the data line can only be changed when SCL is LOW.

Figure 12. Data Validity Diagram

A pullup resistor between the controller's VIO line and SDA must be greater than [(VIO – VOL) / 3 mA] to meet

the VOL requirement on SDA. Using a larger pullup resistor results in lower switching current with slower edges,

while using a smaller pullup results in higher switching currents with faster edges.

7.5.1.2 Start and Stop Conditions

START and STOP conditions classify the beginning and the end of the I2C session. A START condition is

defined as SDA signal transitioning from HIGH to LOW while SCL line is HIGH. A STOP condition is defined as

the SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master always generates START and

STOP conditions. The I2C bus is considered to be busy after a START condition and free after a STOP condition.

During data transmission, the I2C master can generate repeated START conditions. First START and repeated

START conditions are equivalent, function-wise.

12

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