By adding a single component to a 3V-only or 5V-only board, you can operate conventional CMOS analog switches with performance approaching that specified with dual ±15V supplies. This simple modification provides fast switching, low on-resistance, CMOS/TTL compatibility, low-power consumption, and a signal range (±VCC
) that exceeds the input supply range (VCC
Simply add a dual-output charge-pump voltage converter (IC1), which produces ±2VCC
outputs from a single VCC
input. These unregulated voltages ensure reliable switch operation for VCC
levels as low as 2.5V.
Figure 1. The MAX865 dual-output charge pump (IC1) provides a local bipolar power supply for the MAX4659 CMOS analog switch (IC2).
supply voltage of 3V for the MAX865
charge pump produces ±6V rails for the switch (IC2). Using the MAX4659
CMOS analog switch results in a switch on-resistance of less than 30Ω, a transition time of less than 200ns, and low leakage current. Raising the VCC
voltage to 5V generates ±10V rail supplies for the switch, reducing the on-resistance to less than 25Ω and transition times to less than 100ns. See the Typical Operating Characteristics
in the MAX4659 data sheet for more information.
While the charge pump is capable of powering additional switches and/or low-power op amps, more than a few milliamps of load current degrades performance by lowering the unregulated supply rails.