DEMO MANUAL DC2208A LTC4420 18V Dual Input Micropower PowerPath Prioritizer with Backup Supply Monitoring Description Demonstration circuit DC2208A uses the LTC 4420 to the DC2208A is 3.26V to 3.53V. If V2DIS is connected provide backup switchover, keeping the output load pow- to GND, V2UV TEST is ON, and V2 drops below the un- ered during brownout or power loss conditions. Priority is dervoltage level, the LTC4420 disconnects OUT from V2. assigned by supply connection to the V1 and V2 inputs. If the bottom resistor of the divider, R7, is connected to The power source connected to the V1 input has a higher GND, V2 is not monitored for undervoltage condition and priority, and it is monitored continuously by adjustable the load can be powered by any voltage from 1.8V to 18V. comparator (ADJ) with the proper threshold arranged by Recommended V2 voltage is 5V. an external resistive divider. If the input voltage V1 ex- ceeds 1.55V (1.8V worst case) and the ADJ pin is above The LTC4420s internal overcurrent (0.5A to 1.6A) and 1.097V for at least 64ms after V1 has powered up, and thermal protection circuitry allow safe prioritization in then stays above 1.047V, V1 is considered valid, and the critical operation modes. Overtemperature protection LTC4420 connects V1 to load (OUT pin). If V1 drops be- terminates prioritizer operation when the junction tem- low 1.52V, or the ADJ pin voltage is lower than 1.047V, V1 perature exceeds 125C. is considered invalid, and LTC4420 switches V2 to load, Another inherent featurereverse supply protection if the V2DIS pin voltage is above 0.9V. If the V2DIS pin protects the prioritizer input-output and load when voltage is below 0.2V, V2 to load connection is activated negative voltage (up to 15V) is applied to any supply only if V2UV is >0.387V. input, V1 or V2. The DC2208A is populated to provide switchover when V1 The LTC4420s break-before-make switching method pre- is below 9.92V 0.32V. The upper limit for V1 is the maxi- vents cross conduction between input channels during mum operating voltage of 18V recommended V1 voltage switch over connection to any input occurs only if the input is 12V. The resistive divider of the auxiliary comparator voltage exceeds the output by 50mV. This eliminates reverse CMP1, R1R2, is adjusted to trigger the comparator when current flow from the output into selected input supply. VCMP1 TOP turret voltage is in the range 9.82V to 10.69V. Design files for this circuit board are available at The second rail, V2, is monitoring periodically through DEMO MANUAL DC2208A p erformance s Specifications are at T = 25C A SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V Comparator CMP1, V2UV Hysteresis CMP1, V2UV Rising 7.5 10 12.5 mV HYSTC I Switch Current Limit V1 = V2,= 8.4V 0.5 1.1 1.6 A LIM V Reverse Comparator Threshold (V1, V2) V for PowerPath Turn-On 25 50 75 mV REV OUT t Break-Before-Make Time V1 = V2 = 5V, I < 10mA 1 2.5 5 s SWITCH OUT V Demo Board Switchover Voltage 9.6 9.92 10.24 V 1 SWITCHOVER V Demo Board V1 Alarmed Voltage 9.82 10.42 10.69 V 1 ALARM V Demo Board V2UV Voltage 3.26 3.38 3.53 V 2UV t Time Between V2UV Monitoring Event V2TEST 80 132 180 s LTEST o V V W The DC2208A is intended to provide a particular prioritizer V2UV (E7): Undervoltage comparator noninverting input. implementation. VCMP2 TOP (E6): Noninverting input of the comparator The board includes the LTC4420, 18V dual input micro- V2UV for V2 undervoltage monitoring. power PowerPath prioritizer with backup supply monitor- CMP1 (E4): Auxiliary comparator CMP1 noninverting input. ing (U1), LDO regulator with 2.5V output voltage (U2, GND (E5 and E11): Common ground. LT1763) for powering LEDs and logic, dual inverter buf- fer (U3), three LEDs (D7D9) for visual information, two OUT (E9): Terminal for load connection (up to 0.5A). jumpers (JP1, JP2) for selecting a power source for LDO LDO EXT (E14): Positive terminal for external auxiliary and three jumpers (JP4JP6) for setting monitoring pa- 3.5V to 20V power supply. rameters, push button (SW1) for enabling freshness seal mode, a few turrets for connecting the board to power V2P5V (E10): LDO output voltage terminal (2.5V). sources, load and measuring instruments. Auxiliary com- GNDSW (E12): Pulsed GND Output. ponentsLDO and logicare placed on the bottom side. The DC2208A design allows adjusting the operating Jumpers voltage of each channel to any voltage within the full LDO (JP1): ON/OFF switch for powering LDO. operating range. LDO POWER (JP2): Power supply selection for LDO. Provision is made for increasing the hysteresis of the V2UV TEST (JP6): Selection of Monitoring Mode for V2. auxiliary comparator (marked in data sheet as CP1) by placing optional resistor R17. V2DIS (JP4): V2 channel enable or disable. V2TEST (JP5): Enable or disable V2 test. Turrets V1 (E1): 12V supply input the voltage should not exceed LEDs +18V, and should not be lower than 15V. D7: Indicates LDO output voltage. V2 (E8): 5V supply input the voltage should not exceed D8: Indicates first auxiliary comparator output stage +18V, and should not be lower than 15V. (CMPOUT1 pin). ADJ (E3): Adjustable comparator noninverting input for D9: Indicates that V2 is above undervoltage threshold in setting switchover threshold level. the monitoring mode. VCMP1 TOP (E2): Input for voltage monitored by first auxiliary comparator CMP1. dc2208af 2 ie er ummary