Detailed description, Typical operating characteristics (continued), Pin description – Rainbow Electronics MAX1721 User Manual
Page 5
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.
MAX1719/MAX1720/MAX1721
SOT23, Switched-Capacitor
Voltage Inverters with Shutdown
_______________________________________________________________________________________
5
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.)
0
100
50
150
300
350
250
200
400
0
1.0 1.5 2.0 2.5
0.5
3.0 3.5 4.0 4.5 5.0
MAX1719/MAX1721
OUTPUT VOLTAGE RIPPLE vs. CAPACITANCE
MAX1720/21toc15
CAPACITANCE (
µ
F)
OUTPUT VOLTAGE RIPPLE (mVp-p)
V
IN
= +4.75V, V
OUT
= -4.0V
V
IN
= +3.15V, V
OUT
= -2.5V
V
IN
= +1.9V, V
OUT
= -1.5V
50
µ
s/div
MAX1721
START-UP FROM SHUTDOWN
R
L
= 1k
Ω
V
OUT
2V/div
MAX1720/21toc13
V
SHDN
5V/div
Noninverting Shutdown Input. Drive this pin low for normal operation; drive it high for
shutdown mode.
OUT is actively pulled to ground during shutdown.
SHDN
5
Ground
GND
4
Negative Terminal of Flying Capacitor
C1-
3
Power-Supply Positive Voltage Input
IN
2
Inverting Charge-Pump Output
OUT
1
FUNCTION
NAME
0
10
5
20
15
30
25
35
MAX1719/MAX1721
OUTPUT CURRENT vs. CAPACITANCE
MAX1720/21toc14
CAPACITANCE (
µ
F)
OUTPUT CURRENT (mA)
V
IN
= +1.9V, V
OUT
= -1.5V
V
IN
= +4.75V, V
OUT
= -4.0V
V
IN
= +3.15V, V
OUT
= -2.5V
0
1.0 1.5 2.0 2.5
0.5
3.0 3.5 4.0 4.5 5.0
Positive Terminal of Flying Capacitor
C1+
6
Pin Description
Inverting Shutdown Input. Drive this pin high for normal operation; drive it low for
shutdown mode.
OUT is actively pulled to ground during shutdown.
SHDN
–
5
6
–
4
3
2
1
MAX1720
MAX1721
MAX1719
PIN