Datasheet

Operation

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VBIAS, GND Header:—The left pin of this header (VBIAS) connects to R3 and C4. If a thermistor is

installed at RTH, connect the bias supply for the thermistor resistive divider at VBIAS. The right

side of this pin connects to GND.

VI/O, TX Jumper:—The left pin of this jumper (VI/O) connects to the middle pin of the bottom left jumper

on the board (VUSB, VI/O, IN). The right pin (TX) connects directly to the TX1/TORCH input of the

LM3554. There is an internal 300-kΩ pull-down resistor on TX1/TORCH.

VIN/VUSB Jumper:—Left pin of this jumper connects to VL (input side of the inductor). The right pin of

this jumper connects to the USB interface board's power supply.

A2 Header:—The A2 header connects across a 0.1Ω current sense resistor (R2) in series with LED2.

A1 Header:—The A1 header connects across a 0.1Ω current sense resistor (R1) in series with LED1.

SW, GND Header:—The top pin of this header (SW) connects to the SW pin of the LM3554. The bottom

pin connects to GND.

IN, VL Jumper:—The left pin of this jumper connects to IN . The right pin connets to VL (input side of the

inductor). This jumper connects the VL supply to CIN.

VUSB, VI/O, IN Jumper:—Three-pin jumper. The left pin connects to the 3.3V supplied from the USB

Interface Board. The middle pin connects to the LM3554 Evaluation Boards pull-ups. The right pin

connects to IN of the LM3554.

RESET, GND Jumper:—The left pin (RESET) connects to HWEN/GPIO1 of the LM3554 and to the

R_RESET pull-up resistor (10 kΩ). The right pin connects to GND. Connecting a jumper here will

force the LM3554 into shutdown.

VI/O, STROBE Jumper:—Left pin of this jumper connects to the middle pin of the bottom left jumper on

the board (VUSB, VI/O, IN). The right pin connects to the STROBE input on the LM3554.

Connecting a jumper here will force the LM3554 into hardware flash mode.

OUT Header:—This header connects to the OUT pin of the LM3554.

2.2 Operation with the Texas Instruments USB Interface Board

The USBL and USBR connectors (16-pin bottom mounted connectors on each side of the board) plug

directly into the Texas Instruments USB Interface Board. The connectors are keyed so the boards will fit

together only one way. The 3-position header at the bottom left of the board (VUSB, VI/O, IN) connects

the logic voltages to IN or to the 3.3V regulator (VUSB) coming from the USB board. Connecting a jumper

across VIN/VUSB at the top right of the board allows for power (at the VL pin) to come from the Texas

Instruments USB Interface Board. This is useful for demonstrating the device without an external power

supply. This can only be used for low-current Torch and Flash currents which keep the input current below

500 mA. This is due to the 500-mA current limit available from the USB port. This input voltage from the

USB Board can be 3.3V or 5V, depending on the (J1) jumper setting on Texas Instruments USB Interface

Board (See USB Interface Module for Applications (SNOU007) for details). High current requirements

such as the higher Flash and Torch currents require an external supply at VL. Also, ensure the VIN/VUSB

jumper is left open when connecting an external supply to the VL pin when operating with Texas

Instruments USB Interface Board as this will cause a conflict with the power supply from the Interface

Board and the external supply connected to VL.

AN-1742 LM3554 Evaluation Board SNVA646B–January 2009–Revised July 2013

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