DEMO MANUAL DC1973A LT8697 USB 5V 2.5A Output, 42V Input Synchronous Buck with Cable Drop Compensation Description Demonstration circuit 1973A is a USB 5V 2.5A output, 42V When probing the board, pay attention to GND and C GND. input synchronous buck with cable drop compensation On the demonstration board, they are connected together by featuring the LT 8697. The LT8697 is a compact, high default through R13 so a user can connect the ground clip efficiency, high speed synchronous monolithic step-down of a probe to C GND. However, if a user wants to evaluate switching regulator designed to power 5V USB applica- an actual cable, the cable will replace R4 and R13. The tions. Top and bottom power switches, compensation copper between pads of R13 should be cut open. In this components and other necessary circuits are inside of case, C GND is no longer the same as GND. A differential the LT8697 to minimize external components and simplify measurement is needed to probe across the point of load. design. A precise output voltage and programmable cable The demonstration board also includes a USB socket. drop compensation maintain accurate 5V regulation at the With the proper configuration of jumpers X1, X2, X3 and USB socket at the end of a long cable. X4, the USB can be configured for different applications. The circuit runs at 2MHz to minimize external components See Table 1 for configurations. size and to avoid AM band. The demo board has an EMI A 500mA onboard step load can also be activated to evalu- filter installed. The conducted EMI performance of the ate the load transient response of the circuit. To active the board is shown on Figure 2. The figure shows the circuit step load, simply set jumper X5 to V+. passes the EN55022 Class B with a wide margin. The LT8697 data sheet gives a complete description of When the load current is being drawn from VCABLE, the the part, operation and application information. The data load current is limited by the current limit of the LT8697 sheet must be read in conjunction with this quick start or by 5.8V limit at VOUT, whichever comes first. The guide for demo circuit 1973A. rated load current of the demonstration circuit is set at Design files for this circuit board are available at 2.1A, enough for all USB applications. If higher voltage or DEMO MANUAL DC1973A Description Figure 1. LT8697 Demo Circuit EMI Performance, Switching Frequency = 2MHz Table 1. Configure X1 X4 for Different USB Applications X1 X2 X3 X4 J3 Do Not Care Do Not Care Do Not Care OPEN Not in USE OPEN OPEN SHORT SET USB - DCP D+ D- OPEN SET USB - APPLE 2.1A dc1973af 2