MAX1720 View Datasheet(PDF) - ON Semiconductor

Part Name

Description

Manufacturer

MAX1720

Switched Capacitor Voltage Inverter with Shutdown

ON Semiconductor 

MAX1720

Capacitor Selection

In order to maintain the lowest output resistance and

output ripple voltage, it is recommended that low ESR

capacitors be used. Additionally, larger values of C1 will

lower the output resistance and larger values of C2 will

reduce output voltage ripple. (See Equation 3).

Table 1 shows various values of C1, C2 and C3 with the

corresponding output resistance values at 25°C. Table 2

shows the output voltage ripple for various values of C1, C2

and C3. The data in Tables 1 and 2 was measured not

calculated.

Table 1. Output Resistance vs. Capacitance

(C1 = C2 = C3), Vin = 4.75 V and Vout = −4.0 V

C1 = C2 = C3

(mF)

Rout

(W)

0.7

129.1

1.4

69.5

3.3

37.0

7.3

26.5

10

25.9

24

24.1

50

24

Table 2. Output Voltage Ripple vs. Capacitance

(C1 = C2 = C3), Vin = 4.75 V and Vout = −4.0 V

C1 = C2 = C3

(mF)

Output Voltage Ripple

(mV)

0.7

382

1.4

342

3.3

255

7.3

164

10

132

24

59

50

38

Voltage Inverter

The most common application for a charge pump is the

voltage inverter (Figure 14). This application uses two or

three external capacitors. The C1 (pump capacitor) and C2

(output capacitor) are required. The input bypass capacitor,

C3, may be necessary depending on the application. The

output is equal to −Vin plus any voltage drops due to loading.

Refer to Tables 1 and 2 for capacitor selection. The test setup

used for the majority of the characterization is shown in

Figure 14.

Layout Considerations

As with any switching power supply circuit, good layout

practice is recommended. Mount components as close

together as possible to minimize stray inductance and

capacitance. Also, use a large ground plane to minimize noise

leakage into other circuitry.

Capacitor Resources

Selecting the proper type of capacitor can reduce switching

loss. Low ESR capacitors are recommended. The MAX1720

was characterized using the capacitors listed in Table 3. This

list identifies low ESR capacitors for the voltage inverter

application.

Table 3. Capacitor Types

Manufacturer/Contact

AVX

843−448−9411

www.avxcorp.com

Part Types/Series

TPS

Cornell Dubilier

508−996−8561

www.cornell−dubilier.com

ESRD

Sanyo/Os−con

619−661−6835

www.sanyovideo.com/oscon.htm

SN

SVP

Vishay

603−224−1961

www.vishay.com

593D

594

Input Supply Bypassing

The input voltage, Vin should be capacitively bypassed to

reduce AC impedance and minimize noise effects due to the

switching internals in the device. If the device is loaded from

Vout to GND, it is recommended that a large value capacitor

(at least equal to C1) be connected from Vin to GND. If the

device is loaded from Vin to Vout, a small (0.7 mF) capacitor

between the pins is sufficient.

−Vout

+

Vin

+

1

OSC

2

3

6

5

+

4

Capacitors = 10 mF

Figure 18. Voltage Inverter

http://onsemi.com

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