LM3559 datasheet(14/50 Pages) TI1

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LM3559

SNVS624B – JUNE 2011 – REVISED JUNE 2016

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Feature Description (continued)

8.3.3 Independent LED Control

Bits [4:3] of the enable register provide for independent turnon and turnoff of the LED1 or LED2 current sources.

The LED current is adjusted by writing to the Torch Brightness or Flash Brightness Registers. Both the Torch

Brightness and the Flash Brightness Register provide for independent current programming for the LED currents

in either LED1 or LED2. (See Torch Brightness Register and Flash Brightness Register descriptions.)

8.3.4 Hardware Torch

With Configuration Register 1 Bit [7] = 1, TX1/TORCH is configured as a hardware-torch-mode enable. In this

mode (TORCH mode), a high at TX1/TORCH turns on the LED current at the programmed torch current setting.

The STROBE input and I2C-enabled flash takes precedence over torch mode. In hardware-torch mode, both

LED1 and LED2 current sources turn off after a flash event ,and Configuration Register 1 Bit [7] is reset to 0. In

this situation, to re-enter torch mode via hardware torch, the hardware-torch enable bit (Configuration Register 1

Bit [7]) must be reset to 1. Figure 26 details the functionality of the TX1/TORCH/GPIO1 input.

8.3.5 Fault Protections

8.3.5.1 Overvoltage Protection

The output voltage is limited to typically 5 V (5.075 V maximum). In situations such as the current source open,

the LM3559 raises the output voltage in order to keep the LED current at its target value. When VOUT reaches 5

V the overvoltage comparator trips and turns off both the internal NFET and PFET switches. When VOUT falls

below 4.88 V (typical), the LM3559 begins switching again.

8.3.5.2 Current Limit

The LM3559 features 4 selectable current limits: 1.4 A, 2.1 A, 2.7 A, and 3.2 A. These are programmable

through the I2C-compatible interface via bits [6:5] of the Flash Duration Register. When the current limit is

reached, the LM3559 stops switching for the remainder of the switching cycle.

Since the current limit is sensed in the NMOS switch there is no mechanism to limit the current when the device

operates in pass mode. In situations where there could potentially be large load currents at OUT and the LM3559

is operating in pass mode, the load current must be limited to 3 A. In boost mode or pass mode, if VOUT falls

below approximately 2.3 V the part stops switching, and the PFET operates as a current source, limiting the

current to typically 350 mA. This prevents damage to the LM3559 and prevents excessive current draw from the

battery during output short-circuit conditions.

8.3.5.3 Flash Timeout

The flash-timeout period sets the amount of time that the flash current is being sourced from current sources

LED1 and LED2. Bits [4:0] of the Flash Duration Register set the flash-timeout period. There are 32 different

flash-timeout durations in steps of 32 ms giving a flash timeout range of 32 ms to 1024 ms (see Table 5).

8.3.5.4 Indicator LED/Thermistor (LEDI/NTC)

The LEDI/NTC pin serves a dual function, either as a programmable LED message indicator driver, or as a

comparator input for negative temperature coefficient (NTC) thermistors.

8.3.5.4.1

Message Indicator Current Source (LEDI/NTC)

LEDI/NTC is configured as a message indicator current source by setting Configuration Register 1 bit [4] = 0.

The indicator current source is enabled/disabled via Enable Register bit [6]. Enable Register bit [7] programs the

message indictor for blinking mode. When the message indicator is set for blinking mode the pattern

programmed into the Indicator Register and Indicator Blinking Register is sent to the message indicator current

source.

The Indicator Blinking Register controls the following (see Table 17):

1. Number of blank periods (BLANK#. This has 16 settings. tBLANK = tACTIVE × BLANK# , where tACTIVE = tPERIOD

× PERIOD#

2. Pulse width (tPULSE) has 16 settings between 0 and 480 ms in steps of 32 ms. The pulse width is the duration

which the indicator current is at its programmed set point at the end of the ramp-up time.

LM3559 Datasheet(PDF) 14 Page - Texas Instruments

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