Selection of external components for automotive remote antenna voltage regulator and current-sense amplifier

Abstract: This application note helps system designers properly select the external components used with the MAX16946 remote antenna regulator and current-sense amplifier (CSA) to ensure that the automotive antenna detection subsystem meets the target requirements. An electronic calculator is provided to help calculate the parameters of the MAX16946 external key components. The calculator is also used to determine the device's operating range and analog output voltage accuracy.

introduction

The MAX16946 is a high-voltage regulator with a high-precision current-sense amplifier (CSA) designed to provide the hidden power supply for remote antennas in automobiles. The device provides short-circuit protection, current limit protection and open load detection. The current limit of current limit protection and open load protection can be set by external resistors. To ensure that the antenna detection circuit meets the target requirements, the engineer must correctly select external components.

Figure 1 shows the typical application of MAX16946. The main external components and their functions are as follows:

RSENSE is a resistor, through which the load current is detected, and CSA measures and amplifies the voltage across the resistor. Therefore, the sense resistor is very important to determine the overall system accuracy.

R5 and R6 set the regulator output voltage.

The external capacitance of COMP ensures the stability of the regulator under any operating conditions.

R1 and R2 set the current threshold during the fault condition. If the current is maintained at the current threshold for the shielding time of 100ms (minimum), the output is turned off, triggering / SC output low level, retry after 1100ms.

R3 and R4 set the open load detection threshold, when the load current is lower than this threshold, trigger / OL output low level.

When the output is turned off and LOUT attempts to maintain current, the Schottky diode DOUT provides transient negative voltage protection for the MAX16946 OUT pin. Without this diode, OUT may be -0.3V below its absolute maximum voltage, which is not allowed.

Figure 1. Typical operating circuit of the MAX16946 remote antenna CSA and switch

When using CSA and switches for antennas, designers must usually determine the range of working load, normal operating conditions, short circuit and current limit (Figure 2). In addition, the accuracy of the CSA analog output voltage must be verified.

Figure 2. Operating range of the current-sense amplifier

Use the MAX16946 calculator to determine the correct current-sense resistor and resistor divider. These resistor values ​​are used to set the current limit and open load threshold. The calculator considers the tolerance of external components and the MAX16946. By calculating the tolerance range of each design parameter, the designer can ensure that the design parameters are within the range specified by the system specifications.