MAX1697 Maxim, MAX1697 Datasheet - Page 7

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

(Circuit of Figure 1, capacitors from Table 2, V
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
allel with the reservoir capacitor C2. If the voltage across
PIN
1
2
3
4
5
6
500
450
400
350
300
250
200
150
100
NAME
SHDN
50
GND
OUT
C1+
0
C1-
IN
0
OUTPUT RIPPLE vs. CAPACITANCE
_______________________________________________________________________________________
1
2
Detailed Description
Inverting Charge-Pump Output
Power-Supply Voltage Input. Input
range is 1.5V to 5.5V.
Negative Terminal of the Flying
Capacitor
Ground
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 the Flying
Capacitor
IN
V
3
CAPACITANCE ( F)
IN
V
volts. This connects C1 in par-
60mA, SOT23 Inverting Charge Pump
IN
= +4.75V, V
MAX1697T
4
= +3.15V, V
V
IN
5
= +1.9V, V
Pin Description
OUT
6
FUNCTION
OUT
= -4.0V
7
= -2.5V
OUT
8
= -1.5V
IN
9
= +5V, SHDN = IN, T
Typical Operating Characteristics (continued)
10
A
TE: (
Figure 1. Typical Application Circuit
C2 is smaller than the voltage across C1, charge flows
from C1 to C2 until the voltage across C2 reaches
-V
than -V
load drains charge from C2.
The efficiency of the MAX1697 is dominated by its qui-
escent supply current (I
its output impedance (R
is given by:
= +25°C, unless otherwise noted.)
1.5V to 5.5V
IN
C3
INPUT
. The actual voltage at the output is more positive
OFF
IN
ON
500
450
400
350
300
250
200
150
100
50
, since switches S1–S4 have resistance and the
0
0
OUTPUT RIPPLE vs. CAPACITANCE
1
2
5
I
OUT
IN
SHDN
2
I
OUT
V
with Shutdown
IN
V
3
CAPACITANCE ( F)
IN
= +4.75V, V
C1+
6
I
V
MAX1697U
= +3.15V, V
Q
MAX1697
Efficiency Considerations
IN
4
= +1.9V, V
Q
OUT
GND
C1
1
) at low output current and by
5
4
OUT
) at higher output current; it
I
C1-
OUT
6
OUT
= -4.0V
OUT
3
= -2.5V
7
= -1.5V
V
OUT
IN
R
8
OUT
1
9
10
R
L
C2
NEGATIVE
OUTPUT
-1 · V
IN
7