MAX1697 Maxim, MAX1697 Datasheet - Page 9

• Manufacturer Part Number: MAX1697
• Description: 60mA / SOT23 Inverting Charge Pump with Shutdown
• Manufacturer: Maxim

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.
Two devices can be cascaded to produce an even
larger negative voltage (Figure 4). The unloaded output
voltage is normally -2 · V
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 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.
Table 1. Low-ESR Capacitor Manufacturers
Table 2. Capacitor Selection to Minimize
Output Resistance
MAX1697U
MAX1697R
MAX1697S
MAX1697T
Surface-Mount
Tantalum
Surface-Mount
Ceramic
PART
PRODUCTION
METHOD
FREQUENCY
_______________________________________________________________________________________
(kHz)
125
250
12
35
IN
60mA, SOT23 Inverting Charge Pump
MANUFACTURER
, but this is reduced slightly
Paralleling Devices
Cascading Devices
Sprague
CAPACITOR
Matsuo
Matsuo
AVX
AVX
Voltage Inverter
(µF)
6.8
2.2
22
1
TYPICAL
R
OUT
12
12
12
12
593D, 595D series
(Ω)
TPS series
267 series
SERIES
X7R
X7R
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.
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).
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.
Table 3. Capacitor Selection to Minimize
Capacitor Size
MAX1697U
MAX1697R
MAX1697S
MAX1697T
PART
803-946-0690
714-969-2491
603-224-1961
803-946-0690
714-969-2491
FREQUENCY
PHONE
(kHz)
with Shutdown
Heavy Load Connected to a
125
250
12
35
Combined Doubler/Inverter
Layout and Grounding
CAPACITOR
(µF)
0.47
Positive Supply
3.3
10
1
803-626-3123
714-960-6492
603-224-1430
803-626-3123
714-960-6492
FAX
TYPICAL
R
OUT
17
17
17
17
(Ω)
9