SOT23, Switched-Capacitor
Voltage Inverters with Shutdown
MAX1719/MAX1720/MAX1721
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
IN
= +5V, SHDN = GND (MAX1719),
SHDN
= IN (MAX1720/MAX1721), C1 = C2 = C3, T
A
= +25°C, unless
otherwise noted.)
MAX1721
START-UP FROM SHUTDOWN
MAX1720/21toc13
MAX1719/MAX1721
OUTPUT CURRENT vs. CAPACITANCE
MAX1720/21toc14
MAX1719/MAX1721
OUTPUT VOLTAGE RIPPLE vs. CAPACITANCE
350
300
V
IN
= +4.75V, V
OUT
= -4.0V
250
200
150
100
50
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
CAPACITANCE (µF)
V
IN
= +3.15V, V
OUT
= -2.5V
V
IN
= +1.9V, V
OUT
= -1.5V
MAX1720/21toc15
35
30
V
OUT
2V/div
OUTPUT CURRENT (mA)
25
20
15
10
V
IN
= +1.9V, V
OUT
= -1.5V
5
0
V
IN
= +3.15V, V
OUT
= -2.5V
V
IN
= +4.75V, V
OUT
= -4.0V
400
OUTPUT VOLTAGE RIPPLE (mVp-p)
V
SHDN
5V/div
50µs/div
R
L
= 1kΩ
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
CAPACITANCE (µF)
Pin Description
PIN
MAX1719
MAX1720
MAX1721
NAME
FUNCTION
1
2
3
4
5
–
6
1
2
3
4
–
5
6
OUT
IN
C1-
GND
SHDN
SHDN
C1+
Inverting Charge-Pump Output
Power-Supply Positive Voltage Input
Negative Terminal of Flying Capacitor
Ground
Noninverting Shutdown Input. Drive this pin low for normal operation; drive it high for
shutdown mode.
OUT is actively pulled to ground during shutdown.
Inverting Shutdown Input. Drive this pin high for normal operation; drive it low for
shutdown mode.
OUT is actively pulled to ground during shutdown.
Positive Terminal of Flying Capacitor
Detailed Description
The MAX1719/MAX1720/MAX1721 capacitive charge
pumps invert the voltage applied to their input. For high-
est 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
IN
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
IN
. The actual voltage at the output is more positive
than -V
IN
, since switches S1–S4 have resistance and the
load drains charge from C2.
_______________________________________________________________________________________
5
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
