Rainbow Electronics MAX1697 User Manual

Page 9

MAX1697

60mA, SOT23 Inverting Charge Pump

with Shutdown

_______________________________________________________________________________________

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

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
voltage is normally -2

, but this is reduced slightly

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

125

250

6.8

2.2

PART

FREQUENCY

(kHz)

CAPACITOR

(µF)

TYPICAL
R

OUT

(

Ω)