DEMO CIRCUIT 817A QUICK START GUIDE LTC2927 Single Power Supply Tracking Controller DESCRIPTION Demonstration circuit DC817A is intended for Design files for this circuit board are available. evaluating the performance of the LTC2927 Single Call the LTC factory. Power Supply Tracking Controller. The board , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT and PowerPath are trademarks of Linear Technology Corporation. contains two LTC2927s tied to a common ramping signal, providing tracking and sequencing for two power supplies. As assembled, DC817A operates directly with two DC222 buck outputs. PERFORMANCE SUMMARY Specification s are at T = 25C A SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V Input Supply Voltage Range 2.6 5.5 V CC V Supply Undervoltage Lockout V 2.2 2.5 2.7 V CC(UVLO) CC RISING V Supply Undervoltage Lockout Hysteresis 25 mV CC(UVLO) V ON Pin Threshold Voltage V 1.210 1.230 1.250 V ON(TH) ON RISING V ON Pin Hysteresis 30 75 150 mV ON(HYST) V TRACK Pin Voltage V = -10A 0.77 0.8 0.82 V TRACK TRACK V = -1mA 0.77 0.8 0.82 V TRACK V FB Pin Clamp Voltage 1AI 1mA 1.5 2.0 2.3 V FB(CLAMP) FB OPERATING PRINCIPLES The LTC2927 controls the output voltage of a Any slave power supply, which has an accessible power supply by introducing a small current into the inverting feedback node of less than 1.5V, and a supplys feedback node. When this current is at its feedback divider current in the range of 10A to maximum, the supplys output is forced to zero 1mA, may be controlled with the LTC2927. decreasing this current to zero allows the supplys Tracking behavior is configured using two resistors, output to rise to its normal, regulated output. RTA and RTB. A valid Vcc supply for the LTC2927 must be present before the tracked supply is The RAMP pin is driven by an internally generated enabled or powered up. constant current source, which when loaded with capacitor, produces a linear voltage ramp. By Boost converters and certain linear regulators are varying the injected current under the control of this generally incompatible with the LTC2927 control master ramping signal, the slave supply output is technique. made to follow the master ramp in a predictable DC817A includes two LTC2927 controllers driven fashion. by a common ramp signal. The first controller 1 generates the ramp signal and monitors Vcc with the master ramp rate, and RTA1, RTB1, RTA2, and its ON pin. The second controllers RAMP pin is RTB2 to control the relative behavior of the two driven by REMPBUF of the first its ON pin is supplies. Hold-off time, ramp rate, and offset are all defeated by being tied to V . defined by the resistors. For details on calculating CC these component values, consult the LTC2927 data To reconfigure DC817A for use with other supplies, sheet. five components may be changed: C3 to control QUICK START PROCEDURE As a design example, DC817A is populated for The tracking waveforms are shown in Figure 2 and operation with two DC222 slave supplies, using the Figure 3. Also shown in Figure 2 and Figure 3 is an LT1735 Buck Regulator, which are configured for optional enable waveform, which is simply a 3.3V and 2.5V output. The first LTC2927 controls switch closure to ground on U1s ON pin (see the 3.3V supply, while the second controls the 2.5V Figure 1 for location of this pad). This may be supply. driven by an open collector, such as an enable signal from a microcontroller or separate supply Connect the slave supplies as shown in Figure 1, monitor. attaching both the RUN/SS and VOSENSE lines to the DC817A. Next apply 5V to all boards the outputs will begin tracking up once the ON pin of . U1 detects a valid 5V input. Figure 1. Test Setup 2