60mA, SOT23 Inverting Charge Pump

with Shutdown

_______________________________________________________________________________________

9

Surface-Mount

Tantalum

PRODUCTION

METHOD

714-969-2491

803-946-0690

PHONE

603-224-1961

603-224-1430

714-960-6492

803-626-3123

FAX

MANUFACTURER

AVX

Matsuo

Sprague

SERIES

TPS series

267 series

593D, 595D series

714-969-2491

803-946-0690

AVX

Matsuo

714-960-6492

803-626-3123

X7R

X7R

Surface-Mount

Ceramic

Table 2. Capacitor Selection to Minimize

Output Resistance

Table 3. Capacitor Selection to Minimize

Capacitor Size

Table 1. Low-ESR Capacitor Manufacturers

Voltage Inverter

The most common application for these devices is a

charge-pump voltage inverter (Figure 1). This applica-

tion requires only two external components—capacitors

C1 and C2—plus a bypass capacitor, if necessary.

Refer to the

Capacitor Selection section for suggested

capacitor types.

Cascading Devices

Two devices can be cascaded to produce an even

larger negative voltage (Figure 4). The unloaded output

by the output resistance of the first device multiplied by

the quiescent current of the second. When cascading

more than two devices, the output resistance rises dra-

matically. For applications requiring larger negative

voltages, see the MAX865 and MAX868 data sheets.

Paralleling Devices

Paralleling multiple MAX1697s reduces the output resis-

tance. Each device requires its own pump capacitor

(C1), but the reservoir capacitor (C2) serves all devices

(Figure 5). Increase C2’s value by a factor of

n, where n

is the number of parallel devices. Figure 5 shows the

equation for calculating output resistance.

Combined Doubler/Inverter

In the circuit of Figure 6, capacitors C1 and C2 form the

inverter, while C3 and C4 form the doubler. C1 and C3

are the pump capacitors; C2 and C4 are the reservoir

capacitors. Because both the inverter and doubler use

part of the charge-pump circuit, loading either output

causes both outputs to decline toward GND. Make sure

the sum of the currents drawn from the two outputs

does not exceed 60mA.

Heavy Load Connected to a

Positive Supply

Under heavy loads, where a higher supply is sourcing

current into OUT, the OUT supply must not be pulled

above ground. Applications that sink heavy current into

OUT require a Schottky diode (1N5817) between GND

and OUT, with the anode connected to OUT (Figure 7).

Layout and Grounding

Good layout is important, primarily for good noise per-

formance. To ensure good layout, mount all compo-

nents as close together as possible, keep traces short

to minimize parasitic inductance and capacitance, and

use a ground plane.

MAX1697R

MAX1697S

MAX1697T

MAX1697U

12

35

125

250

22

6.8

2.2

1

12

12

12

12

PART

FREQUENCY

(kHz)

CAPACITOR

(µF)

TYPICAL

MAX1697R

MAX1697S

PART

MAX1697T

MAX1697U

FREQUENCY

(kHz)

CAPACITOR

(µF)

TYPICAL

12

35

125

250

10

3.3

1

0.47

17

17

17

17