LP38841EVAL

User's Guide SNVA156A – June 2006 – Revised April 2013 AN-1457 LP3884X-ADJ Evaluation Board 1 Introduction The LP38841-ADJ and LP38842-ADJ are ultra low dropout linear regulators that provide adjustable output voltages and load currents up to 800 mA (LP38841) and 1.5A (LP38842). This document describes the evaluation board provided to demonstrate the performance of these parts. 2 Basic Application Circuit The basic application circuit shown in Figure 1 reflects the electrical connections and component identifiers used on the evaluation board. TP1 TP2 TP6 IN VIN U1 LP3884X-ADJ R3 51k S/D S/D VOUT OUT BIAS GND BIAS 1.2V R1 9.31k C4 220pF C3 4.7 PF ADJ R2 5.62k C1 0.1 PF C2 10 PF TP3 TP4 TP5 GND Figure 1. Basic Application Circuit Schematic 3 Capacitor C4 (Feedforward Compensation) The feedforward capacitor C4 is used to provide increased phase margin. Any good quality X5R/X7R dielectric ceramic capacitor can be used. The value of capacitance for C4 depends on the value of R1. C4 may be calculated using the formula in Equation 1: C4 = 1 / (2 X π X 70k X R1) (1) The value of C4 is calculated after R1 is selected to set the output voltage needed for the specific application. All trademarks are the property of their respective owners. SNVA156A – June 2006 – Revised April 2013 Submit Documentation Feedback AN-1457 LP3884X-ADJ Evaluation Board Copyright © 2006–2013, Texas Instruments Incorporated 1 Setting the Output Voltage 4 www.ti.com Setting the Output Voltage The first build of evaluation boards used R1/R2 values, which set the output voltage to 1.2 V. The nominal output voltage is easily changed by replacing R1. The formula that can be used to calculate the new value of R1 for a different output voltage is shown in Equation 2: VOUT = VADJ (R1/R2) + VADJ (2) Solved for R1: R1 = (VOUT - VADJ) / VADJ X R2 (3) The evaluation board is shipped with a 5.62 kΩ resistor installed at R2. 5 Power Dissipation Power dissipation must be limited so that the junction temperature does not exceed 125°C. Power dissipation can be calculated using Equation 4: PDISS = ((VIN - VOUT) X ILOAD ) + (VIN X IQ(VIN)) + (VBIAS X IQ(VBIAS)) (4) In calculating junction temperature, a value of θJ-A (junction-to-ambient thermal resistance) of approximately 50°C/W should be assumed for this board. Junction temperature (TJ) is calculated using Equation 5: TJ = PDISS X θ(J-A) + TAMBIENT = PDISSX 50 + TAMBIENT (5) Table 1. Component List PCB U1 TP1, TP2, TP3, TP4, TP5, TP6 LP38842 Test point terminal, NEWARK 97H6311 VIN CONNECTOR Banana jack (RED): DIGI-KEY 108-0902-001 VOUT CONNECTOR Banana jack (BLUE): DIGI-KEY 108-0910-001 GROUND CONNECTOR S/D CONNECTOR BIAS CONNECTOR 2 551012613-001 Rev A Banana jack (BLACK): DIGI-KEY 108-0903-001 Banana jack (YELLOW): DIGI-KEY 108-0907-001 Banana jack (GREEN): DIGI-KEY 108-0904-001 R1 Banana, 0805 case, 9.31 kΩ, 1% DIGI-KEY 311-(9.31K)CCT-ND R2 Resistor, 0805 case, 5.62 kΩ, 1% DIGI-KEY 311-(5.62K)CCT-ND R3 R3: resistor, 0805 case, 51 kΩ, 5% DIGI-KEY 311-(51K)ACT-ND C1 Ceramic capacitor, 0805 case, 0.1 µF, X5R/X7R dielectric: DIGI-KEY 478-3351-1-ND C2 Ceramic capacitor, 10 µF, Taiyo-Yuden #LMK325BJ106MN C3 Ceramic capacitor, 4.7 µF, Taiyo-Yuden # JMK316BJ475MD C4 Ceramic capacitor, 0805 case, 220 pF, X5R/X7R dielectric: DIGI-KEY 311-1123-1-ND AN-1457 LP3884X-ADJ Evaluation Board Copyright © 2006–2013, Texas Instruments Incorporated SNVA156A – June 2006 – Revised April 2013 Submit Documentation Feedback PCB Layout Diagram www.ti.com 6 PCB Layout Diagram GND GND TP3 C1 +BIAS SD TP2 TP4 S/D BIAS U1 TP5 R3 TP1 VIN VIN C2 R1 TP6 VOUT C4 R2 VOUT C3 NSC LP3884XMR-ADJ Figure 2. Top View SNVA156A – June 2006 – Revised April 2013 Submit Documentation Feedback AN-1457 LP3884X-ADJ Evaluation Board Copyright © 2006–2013, Texas Instruments Incorporated 3 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. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. 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