Rainbow-electronics MAX1697 Manual de usuario descargar pdf (Pagina 7)

Detailed Description

The MAX1697 capacitive charge pumps invert the volt-

age applied to their input. For highest performance, use

low equivalent series resistance (ESR) capacitors (e.g.,

ceramic).

During the first half-cycle, switches S2 and S4 open,

switches S1 and S3 close, and capacitor C1 charges to

the voltage at IN (Figure 2). During the second half-

cycle, S1 and S3 open, S2 and S4 close, and C1 is level

shifted downward by V

volts. This connects C1 in par-

allel with the reservoir capacitor C2. If the voltage across

C2 is smaller than the voltage across C1, charge flows

from C1 to C2 until the voltage across C2 reaches

-V

. The actual voltage at the output is more positive

than -V

, since switches S1–S4 have resistance and the

load drains charge from C2.

Efficiency Considerations

The efficiency of the MAX1697 is dominated by its qui-

escent supply current (I

) at low output current and by

its output impedance (R

OUT

) at higher output current; it

is given by:

I x R

OUT

OUT Q

OUT OUT

η≅

−













MAX1697

60mA, SOT23 Inverting Charge Pump

with Shutdown

_______________________________________________________________________________________ 7

100

200

150

300

250

350

450

400

500

0 2341 567 9810

MAX1697T

OUTPUT RIPPLE vs. CAPACITANCE

MAX1697 TOC27

CAPACITANCE (µF)

OUTPUT RIPPLE (mV)

= +1.9V, V

OUT

= -1.5V

= +3.15V, V

OUT

= -2.5V

= +4.75V, V

OUT

= -4.0V

100

200

150

300

250

350

450

400

500

0 2341 567 9810

MAX1697U

OUTPUT RIPPLE vs. CAPACITANCE

MAX1697 TOC28

CAPACITANCE (µF)

OUTPUT RIPPLE (mV)

= +1.9V, V

OUT

= -1.5V

= +3.15V, V

OUT

= -2.5V

= +4.75V, V

OUT

= -4.0V

Pin Description

Positive Terminal of the Flying

Capacitor

Inverting Charge-Pump Output

Power-Supply Voltage Input. Input

range is 1.5V to 5.5V.

Negative Terminal of the Flying

Capacitor

4 Ground

Shutdown Input. Drive this pin high

for normal operation; drive it low for

shutdown mode. OUT is actively

pulled to ground during shutdown.

PIN FUNCTIONNAME

C1+

OUT

C1-

GND

SHDN

Typical Operating Characteristics (continued)

(Circuit of Figure 1, capacitors from Table 2, V

= +5V, SHDN = IN, T

= +25°C, unless otherwise noted.)

E: (

OFF

C1+ C1-

SHDN

OUT

GND

INPUT

1.5V to 5.5V

NEGATIVE

OUTPUT

-1

MAX1697

Figure 1. Typical Application Circuit

1 2 3 4 5 6 7 8 9 10 11

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Rainbow-electronics MAX1697 Manual de usuario Pagina 7

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