LM2796TLEV

User's Guide SNVA086A – May 2004 – Revised April 2013 AN-1321 LM2796 Evaluation Board 1 Board Operation 1.1 Basic Connections To operate the LM2796 evaluation board, connect a supply voltage (2.7V-5.5V) between board connectors VIN and GND. Default Jumper Connections: • EN: Connects the “+” post to the middle post of the EN header strip. This connects VIN to the EN pin of the LM2796, enabling the part. • ENA: Connects the “+” post to the middle post of the ENA header strip. This connects VIN to the ENA pin of the LM2796, enabling D1A-D4A outputs • ENB: Connects the “+” post to the middle post of the ENB header strip. This connects VIN to the ENB pin of the LM2796, enabling D1B-D3B outputs. • LEDS_ON: Jumper connects the two posts of the LEDS_ON header strip. This connects the cathodes of all 7 LEDs to GND, establishing the LED current path. When these connections are all made correctly, all LEDs will be ON. 1.2 RSET: Setting LED Currents The resistance of the RSET resistor sets the DC output currents of the LM2796 according to equation: IDxx = 100 X (1.25V / Rset) (1) The default RSET on the evaluation board is 8.3kΩ and gives a DC output current of 15mA (typ.). Component Rset’ is an optional leaded resistor replacement for the surface mount Rset, provided for ease of use. 1.3 EN, ENA, and ENB Headers: LED Activation and PWM Brightness Control The header strips EN, ENA, and ENB can be used to enable/disable the LM2796 and/or the LED (output) currents. The connections to the ENx pins provided by these posts can also be used to connect pulsewidth modulated (PWM) signals to the LM2796 in order to adjust the average brightness of the LEDs. On each of these header strips, the post labeled “+” is connected to VIN. The post labeled “-“ is connected to GND. The middle post connects to EN, ENA, and ENB, respectively. Jumpers can be used to connect each ENx pin to either VIN or GND. Connecting EN to VIN enables the charge pump and other internal circuitry of the LM2796. Connecting EN to GND places the part in Shutdown mode. When the part in enabled (EN = VIN), connecting ENA to VIN enables the D1A-D4A LEDs. Connecting ENA to GND disables these LEDs. Similarly, connecting ENB to VIN enables the D1B-D3B LEDs, and connecting ENB to GND disables them. A pulse signal (PWM) can be connected to the ENA and/or ENB pins to adjust the brightness of the respective LED banks. The duty cycle of the pulse signal determines the net brightness, as perceived by the human eye. For example, with a duty cycle of 50%, the LEDs will only be ON for 50% of the time, and the perceived brightness will be approximately half of what the brightness is when the output current flows continuously through the LEDs. Recommended frequency range for PWM signals: 100Hz to 1kHz. All trademarks are the property of their respective owners. SNVA086A – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1321 LM2796 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 1 Board Operation www.ti.com It is recommended that ENA and ENB pins be used for PWM brightness adjustment (dimming). Toggling the voltage on these pins turns the internal LM2796 current sources on and off, and the charge pump stays ON continuously. Placing a PWM signal on the EN pin repeatedly turns the internal charge pump ON and OFF. Each time the charge pump is activated, significant inrush current can be expected as the large external capacitors are quickly recharged. This could inject noise on the input line. 1.4 Using the LEDS on Headers to Measure Output Currents or to Drive Different LEDS By removing the LEDS_ON jumper, LM2796 output currents can easily be measured. Removing the jumper disconnects the cathodes of all LEDs from GND, breaking the LED current paths. By placing a current meter between the two header pins, as shown on the following page in Figure 1, the sum total of all LED currents can be measured. With the LEDS_ON jumper removed, the current of an individual output can be measured by placing a current meter between a Dxx header and GND, as shown in Figure 2. With such a connection, the voltage on pin Dxx will be almost 0V because the series resistance of the current meter is likely to be quite small. Since the regulated output currents of the LM2796 are almost completely independent of Dxx pin voltage (provided VDxx is not too high to inhibit regulation), this measurement will still be quite accurate. With the LEDS_ON jumper removed, the LM2796 can drive external LEDs simply by connecting each LED between a Dxx output and GND. The LEDs on the evaluation board need not be removed for this type of test/evaluation. C1 1 PF C1+ VIN 2.7V to 5.6V C2 1 PF C1- C2+ C2- EN ENA ENB POUT VIN 3/2× Charge Pump LM2796 CIN CPOUT 1 PF 1 PF ISET GND D1A D2A D3A D4A D1B D2B D3B RSET LEDS_ON+ A I = 6 IDxx LEDS_ON- Figure 1. Measuring Current of all LEDs by Removing LEDs_ON Jumper and Placing a Current Meter Between the Two LEDS_ON Header Posts 2 AN-1321 LM2796 Evaluation Board SNVA086A – May 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Board Operation www.ti.com C1 1 PF VIN 2.7V to 5.6V C1+ C2 1 PF C1- C2+ C2- EN ENA ENB POUT VIN 3/2× Charge Pump CIN CPOUT LM2796 1 PF 1 PF ISET GND D1A D2A D3A D4A D1B D2B D3B RSET VD1A | 0V I = ID1A A LEDS_ON+ VD3B | VLEDm I=0 ALL LEDs OFF I = ID3B A Series LED or Resistor Optional to Set VDxx | 3.6V LEDM Figure 2. Measuring Current of All Individual Dxx Outputs by Removing the LEDS_ON Jumper and Placing Current Meters Between the Dxx Pins and GND SNVA086A – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1321 LM2796 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 3 Schematic 2 www.ti.com Schematic EN C1 1 PF VIN C1+ 2.7V to 5.5V VIN C2 1 PF C1- C2+ C2- + ENA + ENB + - - - EN ENA ENB POUT 3/2× Charge Pump CIN LM2796 CPOUT 1 PF 1 PF ISET GND D1A D2A D3A D4A D1B D2B D3B RSET or RSET¶ D1B-D3B D1A-D4A LEDS_ON 3 4 Bill of Materials Component Symbol Value Package [U.S. (Metric)] Dimensions (mm) Temperature Characteristic Manufacturer Part # LM2796 -- YZR0018 DSBGA 2.1 x 2.4 x 0.6 -- Texas Instruments LM2796 Cin, Cout 2.2µF, 6.3V 0603 (1608) 1.6 x 0.8 x 0.8 X5R TDK C1608X5R0J225K C1, C2 1µF, 10V 0603 (1608) 1.6 x 0.8 x 0.8 X5R TDK C1608X5R1A105K Dxx White LEDs -- 1.5 x 2.3 x 1.4 -- OSRAM LWM67C-T1U1-3C5D Rset 8.3kΩ 0603 (1608) 1.6 x 0.8 x 0.8 -- Vishay-Dale CRCW06048251F Rset' (optional) -- -- -- -- -- AN-1321 LM2796 Evaluation Board SNVA086A – May 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated LM2796 Evaluation Board Layout www.ti.com 4 LM2796 Evaluation Board Layout Figure 3. Top Layer Figure 4. Bottom Layer (top view, unmirrored) SNVA086A – May 2004 – Revised April 2013 Submit Documentation Feedback AN-1321 LM2796 Evaluation Board Copyright © 2004–2013, Texas Instruments Incorporated 5 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. 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