Maxim MAX6877 User's Manual
Contents
1. case tpeLay becomes the default 200us 5 Pick the MOSFETs for each channel Ensure that the MAX6877 gate drive circuit can drive the gate capacitance of the MOSFET Multiple MAX6877 parts can be connected together by connecting the power good output of the first device to the enable input EN active low UV of the next device For more information see the data sheet Application Note 3918 www maxim ic com an3918 More Information For technical Support www maxim ic com support For samples www maxim ic com samples Other questions and comments www maxim ic com contact Automatic Updates Would you like to be automatically notified when new application notes are published in your areas of interest Sign up for EE Mail Related Parts MAX6877 QuickView Full PDF Data Sheet Free Samples AN3918 AN 3918 APP3918 Appnote3918 Appnote 3918 Copyright by Maxim Integrated Products Additional legal notices www maxim ic com legal2. SAXLAVI Maxim gt App Notes gt MICROPROCESSOR SUPERVISOR CIRCUITS Keywords sequencing sequencer monitor reset voltage tracking voltage tracker Sep 20 2006 APPLICATION NOTE 3918 User s Guide for the MAX6877 Power Supply Tracker Sequencer Abstract This application note is a step by step User s Guide for designing with the MAX6877 voltage tracker and sequencer The note explains how to make suitable component calculations FROM DC DCs 3 3v I TO LOADS i 1 5 wv G O a a Hi HE IN1 IN2 INS GATE GATE GATES TRACKING MODE SET1 OUT MAAXLAA OUT2 _ akak MAX6B77 OUTS SLEW TIMEOUT ABP Cear T Cstew Crmeout 1uF j 4 I SEQUENCING MODE GAD MARGIN TRAISEQ FAULT AND PORST OMITTED FOR CLARITY Figure 1 The basic circuit for the MAX6877 MAX6877 Overview Tracks or sequences up to three voltages Closed loop tracking control with programmable slew rate Program thresholds with resistors Program slew rate and timing delays with capacitors Fault output and power good output Description The MAX6877 voltage tracker Sequencer can track or sequence up to three voltages Use the TRACK SEQ pin to select tracking or sequencing The device will either track or sequence the three voltages but it cannot track and sequence simultaneously Power up begins when EN active low UV is asserted and all three input voltages are above their thresholds In the example circuit in Figure 1 EN active low UV is con
3. nected to the 12V bus so the circuit will turn on when the bus exceeds its threshold and turn off when it falls under its threshold To create a basic design with the MAX6877 such as the one in Figure 1 follow these steps 1 Select the input voltage thresholds for IN1 IN2 and IN3 The input voltages must exceed these thresholds for power up to begin Use the following formula to set the resistor divider values for IN1 For IN2 or IN3 replace R with R3 or Rs and R gt with Rg or Re VIHRESH 0 5 a 2 Select the EN active low UV threshold using the following formula EN active low UV can also be used as a logic level input to control power up If not used connect EN active low UV to ABP VTHRESH 1 286 x 1 a 3 Set the voltage slew rate This is the rate at which the voltages at the outputs OUT1 OUT2 OUT3 ramp up and down Select capacitor Cc pw by using the following formula _ 9 35 x 10 SR CSLEW where Coc Fw is in farads and SR is in V s Cc pw must be in the range of 100pF lt Co ew lt 1nF 4 In sequencing mode only the voltages come up one after another separated by a time delay which is set by Capacitor Cpe ay using the following formula tneLay 200us 500KQ2 x Cpe ay where CpeLay IS in farads and tpg ay iS in seconds tpg ay is also the delay time from when all thresholds are exceeded to the start of sequencing or tracking Cpg ay can be safely left out of the circuit in which
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