DC2118A Analog Devices

DEMO MANUAL DC2118A LTC4040 Battery Charger and Backup Power Manager DESCRIPTION Demonstration circuit 2118A is a combination step-down and status indicated by the FAULT LED. Charging can be battery charger and step-up battery backup regulator us- enabled/disabled with the ENCHG jumper. ing the LTC 4040 monolithic system power manager. The Battery Backup DC2118A has an input voltage range from 4.8V to 5.5V with overvoltage protection (OVP) to 40V, as limited by Following an input power failure, the circuit automatically the external MOSFET. The input current is monitored to shifts to battery backup boost mode to regulate the VSYS prioritize the load up to the 2.5A threshold before charge output rail. The backup mode system output voltage is current is reduced. initially programmed for 5V. The input power failure status is indicated by the PFO LED. Battery Charging If VSYS ever falls below the programmed reset threshold As initially configured, DC2118A is programmed for 2A voltage, the RST LED will change states to indicate the charge current limit when in charge mode. The charge need to reset the system and recharge the battery. Backup voltage is jumper-selectable in 8 discrete steps from regulation can be enabled/disabled with the ENBST jumper. 3.45V to 3.6V for LiFePO chemistry or 3.95V to 4.1V for 4 For convenience, all LEDs can be disabled with the LED Li-ion chemistry, according to the F2/F1/F0 programming jumper to reduce the quiescent current of the system. input settings. Design files for this circuit board are available at The charge current limit is adjustable via the PROG pin I (A) BAT V + V (V) BAT CHRG DEMO MANUAL DC2118A PERFORMANCE SUMMARY 2.25 4.2 5 5 V SYS BACKUP POWER 2.00 4.0 V BAT STARTED FAIL TIMER 9600mAh Li-Ion 4 4 START 1.75 3.8 V = 5V IN RPROG = 1.00k 1.50 3.6 I V BAT BAT 3 3 1.25 3.4 TERMINATION I BAT 1.00 3.2 CHRG 2 2 0.75 3.0 TIMER 0.50 2.8 1 1 9600mAh Li-Ion RESTART V = 5V 0.25 2.6 SYS C/8 I = 2A SYS 0 2.4 0 0 0 1 2 3 4 5 6 7 8 9 10 0:00 0:30 1:00 1:30 2:00 2:30 TIME (Hrs) TIME (Hrs) dc2118 F01 dc2118a F02 Figure 1. Typical Battery Charge Cycle Figure 2. Typical Battery Discharge Cycle QUICK START PROCEDURE Demonstration circuit 2118A is easy to set up to evaluate NOTE: While DC2118A is robust to overvoltage condi- the performance of LTC4040. Refer to Figure 2 for proper tions up to 40V on DCIN, DO NOT exceed this limit or measurement equipment setup and follow the procedure damage may occur to MOSFET Q1 and IC U1. below. 5. Turn on and adjust the system load as necessary. 1. The jumpers are set as below for a typical 4.1V charg- Charging current will be limited when input current ing application: exceeds 2.5A. JP1 NTC INT 6. The CHRG LED will toggle off when the charge current has dropped below 250mA. The timer will continue to JP2 ENCHG ON run and charging will continue until the timer period JP3 ENBST ON ends. Multiple timer periods may be necessary to fully charge a large capacity battery, such as the one used JP4 F1 1 to obtain Figure 1. JP5 F0 1 7. If the battery voltage does not increase above the low JP6 LEDS ON battery threshold during the precondition time or the thermistor value exceeds the normal range, CHRG will JP7 F2 1 toggle off and FAULT will toggle on indicating a bad 2. With all power off, connect the input supply, system battery. load, and meters as shown in Figure 3. Backup Mode Charge Mode 8. Turn off the input power supply to evaluate backup 3. Connect the battery as shown in Figure 3 to charge at mode. 4.1V, 2A. For alternate charge voltage settings, refer 9. The PFO LED will toggle on indicating input power to Table 1. failure. 4. Turn on the input power supply to evaluate charge 10. Adjust the system load as necessary. mode. Adjust the input voltage and current limit to the desired value. dc2118af 2 I (A) BAT V (V) BAT