DEMO CIRCUIT 818 LTC2924 QUICK START GUIDE LTC2924 Quad Power Supply Sequencer DESCRIPTION Demonstration circuit 818 is a Quad Power Supply Se- The circuit board is assembled with four IRL3714ZS N- quencer featuring the LTC2924. channel DD packaged MOSFETs capable of controlling up to 10A loads for connecting each of four rails with the an Demonstration circuit 818 can configure the LTC2924 to associated load. The board is designed to also accept sequence up to 4 power supplies via any combination of SO-8 packaged MOSFETs for lower current operation. pass FETS or power supply enable control inputs. The In addition to the output voltage dividers, the circuit 0.61V reference of the LTC2924 permits the DC818 to be board also has two capacitors for sequence and Power easily modified by simple resistor changes to work with Good signal timing adjustments, one resistor for setting any voltage level from 5V down to 0.8V. The schematic the hysteresis current injected into each output voltage provides a table of resistor values for common supply divider and two configuration jumpers for cascading voltages: 5V, 3.3V, 3.0V, 2.8V, 2.5V, 1.8V, 1.6V, 1.2V and boards for additional channels. 1.0V. Refer to the data sheet for equations to calculate LTC is a trademark of Linear Technology Corporation other voltages and hysteresis levels. Convenient test points are provided to facilitate evaluation of the power up and power down sequencing. Additional jumper op- tions are provided to permit cascading multiple DC818s for additional channels. PERFORMANCE SUMMARY SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V Input Supply Range 3.0 6.0 V CC I Input Supply Current V = 3.6V, I = 100mA 1.5 3.0 mA CC IN LOAD V ON, Low to High Threshold 0.6000 0.6060 0.6121 V ON(TH) V ON, High to Low Threshold 0.6013 0.6074 0.6135 V OFF(TH) V IN1-IN4 Low to High Threshold 0.6020 0.6081 0.6142 V INON(TH) V IN1-IN4 High to Low Threshold 0,6026 0.6087 0.6148 V INOFF(TH) V OUT1-OUT4 Gate Drive Voltage V +4.5 V +6 V OUT(EN) CC CC I OUT1-OUT4 On Current 8.6 10 11.2 A OUT(EN) OPERATING PRINCIPLES The active high ON pin initiates the power on sequence LTC2924 enables a successive power supply. Each sup- when the applied voltage exceeds 0.61V. Upon sequence ply is enabled by driving a 10uA current out of the appro- initiation, the Sequencer TIMER capacitor C is charged priate OUTn pin. This current is derived from a charge TMR by a 5uA current, generating a sequencing time pulse of pump capable of enhancing the gate of a NMOS pass FET C (uF)/5. At the end of each sequence timeout, the or driving a power supply enable pin. A capacitor can be TMR LTC2924 connected to the OUTn pins to control the slew rate of the last power supply has turned on. The power off se- each MOSFET controlled supply. quence is initiated by pulling the ON pin voltage below 0.61V after a power on sequence has completed. The As the power supply turns on, the resistive divider con- power off sequence turns off the power supply in the re- nected to the IN1 pin starts to drive up the voltage at the verse order of the power on sequence. OUT4 is turned off IN1 pin. When the voltage at this pin exceeds 0.61V, a first. The timer function is used between each supply be- comparator signals the logic that the supply is on. The ing sequenced down. timer circuit is enabled again and the cycle repeats until QUICK START PROCEDURE Demonstration circuit 818 is easy to set up to evaluate the data sheet to change the dividers to support other the performance of the LTC2924. voltages. Install all four jumpers in position 1. Attach optional loads to TP11, TP12, TP13 and TP14 (up to 10 amps depending on acceptable voltage drop). Connect an ON signal source to the ON pin circuit (TP7 or TP8, the latter provides a voltage divider which can be Initiate the turn on sequence by raising the ON signal configured as an under voltage lockout.) The voltage on source so that TP7 is above 0.62V and observe the load TP7 should be less than 0.55V. voltage transitions on the four channel scope (see figure 1). Connect four external power supply outputs (3.3V, 2.5V, 1.8V, and 1.2V) to appropriate INPUT pins (TP3, TP4, Drop the ON pin voltage below 0.55V (or to ground) to TP5, and TP6). Refer to the table on the schematic or observe the turn off sequence (see Figure 2). NOTE: Output voltage decay will vary with load and capacitance. Figure 1. Power up mode