IS31LT3954A IS32LT3954A DEMO BOARD GUIDE DESCRIPTION FEATURES The IS31LT3954A/IS32LT3954A is a DC-to-DC Wide input voltage supply from 4.5V to 38V switching converter that integrates an N-channel - Withstand 40V load dump MOSFET to operate in a buck configuration. The True average output current control device can operate from a wide input voltage 3A maximum output over operating temperature between 4.5V and 38V and provides a constant range current of up to 3A for driving a single LED or multiple Cycle-by-cycle current limit series connected LEDs. Integrated high-side MOSFET switch The external resistor, R , is used to set a constant ISET Dimming via direct logic input or power supply LED output current, while allowing the output voltage voltage to be automatically adjusted for a variety of LED Internal control loop compensation configurations. Under-voltage lockout (UVLO) and thermal The IS31LT3954A/IS32LT3954A operates in a fixed shutdown protection frequency mode during switching. There is an 2 A low power shutdown external resistor connected between the VCC and Spread spectrum to optimize EMI TON pins used to configure the on-time (switching Robust fault protection and reporting function: frequency). The switching frequency is dithered for - Pin-to-GND short spread spectrum operation which will spread the electromagnetic energy into a wider frequency band. - Component open/short faults This function is helpful for optimizing EMI - Adjacent pin-to-pin short performance. - LED open/short - Thermal shutdown A logic input PWM signal applied to the enable (EN) Shared fault flag for multiple device operation to pin will adjust the average LED current. The LED meet One-Fail-All-Fail brightness is proportional to the duty cycle of the PWM signal. AEC-Q100 Qualified - IS32LT3954A only True average output current operation is achieved with fast transient response by using cycle-by-cycle, RECOMMENDED EQUIPMENT controlled on-time method. In addition, IS31LT3954A/IS32LT3954A integrates 38VDC power supply various fault protections for robust operation. 1 pcs of LED panel (3W LEDs, 4LEDs in parallel Detection of these faults is reported by the FAULTB and then 10 LEDs in series on each panel) I/O pin. Multiple devices can have their FAULTB pins Multi-meter connected to create a One-Fail-All-Fail system operation. RECOMMENDED INPUT AND OUTPUT RATINGS The IS31LT3954A/IS32LT3954A is available in an SOP-8-EP package with an exposed pad for Input: 4.5~38VDC enhanced thermal dissipation. It operates from 4.5V Output: 1~10 LEDs in series/3A to 38V over the temperature range of -40C to +125C. ABSOLUTE MAXIMUM RATINGS QUICK START Input voltage 42VDC Caution: Do not exceed the conditions listed above, otherwise the board will be damaged. PROCEDURE The IS31LT3954A/IS32LT3954A DEMO Board is fully assembled and tested. Follow the steps listed below to verify board operation. Caution: Do not turn on the power supply until all connections are completed. 1) Connect the positive terminal of the power supply to the VCC of the board and the negative terminal Figure 1: Photo of IS31LT3954A/IS32LT3954A Evaluation Board of the power supply to the GND of the board. Lumissil Microsystems www.lumissil.com 1 Rev. C, 09/15/2020 IS31LT3954A IS32LT3954A DEMO BOARD GUIDE 2) Connect the negative of the one of the LED panel the PWM signal, the JP6 must be open to avoid (LED arrays) to the LED- terminal. And connect PWM generator damage. the positive of the LED panel (LED arrays) to the 5) Set FAULTB pin to VCC by JP5 or feedback to a LED+ terminal. MCU. Note: when feedback to the MCU, the JP5 3) Select R register on the DEMO Board by must be open and pulled up on MCU site to avoid ISET JP1~JP4 to set output current, that I =0.2/ MCU damage. OUT R . ISET 6) Turn on the power supply and the LED panels 4) Select EN/PWM pin to VCC by JP6 or connect to (LED arrays) will be lighted up. a PWM signal generator. Note: when connect to ORDER INFORMATION Part No. Temperature Range Package IS31LT3954A-GRLS4-EB -40C to +125C (Industrial) SOP-8-EP, Lead-free IS32LT3954A-GRLA3-EB -40C to +125C (Automotive) For pricing, delivery, and ordering information, please contacts Lumissils analog marketing team at analog Lumissil.com or (408) 969-6600. 2.2 DETAILED DESCRIPTION 2 OUTPUT CURRENT SETTING 1.8 1.6 The LED current is configured by an external sense 1.4 resistor, R , with a value determined as follows ISET 1.2 Equation (1): 1 I V /R (1) 0.8 LED FB ISET 0.6 Where V = 0.2V (Typ.). FB 0.4 Note that R = 0.0667 is the minimum allowed ISET 0.2 value of sense resistor to maintain switch current 0 0 100 200 300 400 500 600 700 800 900 1000 1100 below the specified maximum value. RTON (k ) Table 1 R Resistance Versus Output Current ISET Figure 2 Operating Frequency vs. R Resistance TON R ( ) Nominal Average Output Current (mA) ISET The approximate operating frequency can be 0.2 1000 calculated by below Equation (2) and (3): 0.1 2000 k R R V TON INT OUT t (2) ON 0.0667 3000 V CC The R should be a 1% resistor with enough power ISET tolerance and good temperature characteristic to 1 f (3) SW ensure accurate and stable output current. k R R TON INT FREQUENCY SELECTION Where k= 0.00458, with f in MHz, t in s, and R SW ON TON During switching the IS31LT3954A/IS32LT3954A and R (internal resistance, 20k ) in k. INT operates in a consistent on-time mode. The on-time is Higher frequency gets smaller components size but adjusted by an external resistor, R , which is TON increases the switching losses and high-side MOSFET connected between the VCC and TON pins. gate driving current, and may not allow sufficiently high or low duty cycle. Lower frequency gives better performance at larger components size. INDUCTOR Inductor value involves trade-offs in performance. Larger inductance reduces inductor current ripple that Lumissil Microsystems www.lumissil.com 2 Rev. C, 09/15/2020 fSW (MHz)