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MAX660

SNOS405B – NOVEMBER 1999 – REVISED MAY 2017

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Copyright © 1999–2017, Texas Instruments Incorporated

10 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

10.1 Application Information

The MAX660 CMOS charge-pump voltage converter is a versatile, unregulated switched-capacitor inverter or

doubler. Operating from a wide 1.5-V to 5.5-V supply voltage, the MAX660 uses two low-cost capacitors to

provide 100 mA of output current without the cost, size, and EMI related to inductor-based converters. With an

operating current of only 120 µA and operating efficiency greater than 90% at most loads, the MAX660 provides

ideal performance for battery-powered systems. MAX660 devices can be operated directly in parallel to lower

output impedance, thus providing more current at a given voltage.

10.2 Typical Applications

10.2.1 Voltage Inverter

Figure 14. MAX660 Voltage Inverter

10.2.1.1 Design Requirements

For typical switched capacitor applications, use the parameters in Table 2:

Table 2. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Input voltage

5.5 V (maximum)

Negative output voltage

–1.5 V to –5.5 V

Output current

100 mA

10.2.1.2 Detailed Design Procedure

The main application of MAX660 is to generate a negative supply voltage. The voltage inverter circuit uses only

two external capacitors as shown in the Figure 14. The range of the input supply voltage is 1.5 V to 5.5 V. For a

supply voltage less than 3.5 V, the LV pin must be connected to ground to bypass the internal regulator circuitry.

This gives the best performance in low-voltage applications. If the supply voltage is greater than 3.5 V, LV may

be connected to ground or left open. The choice of leaving LV open simplifies the direct substitution of the

MAX660 for the LMC7660 switched capacitor voltage converter.

The output characteristics of this circuit can be approximated by an ideal voltage source in series with a resistor.

The voltage source equals

−(V+). The output resistance Rout is a function of the ON resistance of the internal

MOS switches, the oscillator frequency, and the capacitance and ESR of C1 and C2. A good approximation is: