MAX1720EUT-T [MAXIM]

Switched Capacitor Converter, 0.025A, 21kHz Switching Freq-Max, CMOS, PDSO6, SOT-23, 6 PIN;
MAX1720EUT-T
型号: MAX1720EUT-T
厂家: MAXIM INTEGRATED PRODUCTS    MAXIM INTEGRATED PRODUCTS
描述:

Switched Capacitor Converter, 0.025A, 21kHz Switching Freq-Max, CMOS, PDSO6, SOT-23, 6 PIN

光电二极管
文件: 总8页 (文件大小:563K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
19-1439; Rev 2; 4/04  
SOT23, Switched-Capacitor  
Voltage Inverters with Shutdown  
General Description  
Features  
The ultra-small MAX1719/MAX1720/MAX1721 monolithic,  
CMOS charge-pump inverters accept input voltages  
ranging from +1.5V to +5.5V. The MAX1720 operates at  
12kHz, and the MAX1719/MAX1721 operate at 125kHz.  
High efficiency, small external components, and logic-  
controlled shutdown make these devices ideal for both  
battery-powered and board-level voltage conversion  
applications.  
1nA Logic-Controlled Shutdown  
6-Pin SOT23 Package  
99.9% Voltage Conversion Efficiency  
50µA Quiescent Current (MAX1720)  
+1.5V to +5.5V Input Voltage Range  
25mA Output Current  
Oscillator control circuitry and four power MOSFET  
switches are included on-chip. A typical MAX1719/  
MAX1720/MAX1721 application is generating a -5V  
supply from a +5V logic supply to power analog circuitry.  
All three parts come in a 6-pin SOT23 package and can  
deliver a continuous 25mA output current.  
Requires Only Two 1µF Capacitors  
(MAX1719/MAX1721)  
For pin-compatible SOT23 switched-capacitor voltage  
inverters without shutdown (5-pin SOT23), see the  
MAX828/MAX829 and MAX870/MAX871 data sheets. For  
applications requiring more power, the MAX860/MAX861  
Ordering Information  
deliver up to 50mA. For regulated outputs (up to -2 x V ),  
IN  
refer to the MAX868. The MAX860/MAX861 and MAX868  
are available in space-saving µMAX packages.  
PIN-  
SOT  
PART  
TEMP RANGE  
PACKAGE TOP MARK  
MAX1719EUT -40°C to +85°C 6 SOT23-6  
MAX1720EUT -40°C to +85°C 6 SOT23-6  
MAX1721EUT -40°C to +85°C 6 SOT23-6  
AACA  
AABS  
AABT  
Applications  
Local Negative Supply from a Positive Supply  
Small LCD Panels  
GaAs PA Bias Supply  
Handy-Terminals, PDAs  
Battery-Operated Equipment  
Pin Configuration  
Typical Operating Circuit  
1µF  
TOP VIEW  
OUT  
IN  
1
2
3
C1+  
6
5
4
C1+  
C1-  
OUT  
NEGATIVE  
OUTPUT  
INPUT  
1.5V to 5.5V  
IN  
-1 · V  
IN  
MAX1719  
MAX1720  
MAX1721  
SHDN (SHDN)  
GND  
25mA  
MAX1721  
1µF  
C1-  
SHDN  
ON  
OFF  
GND  
SOT23-6  
( ) ARE FOR MAX1719  
________________________________________________________________ Maxim Integrated Products  
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at  
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.  
SOT23, Switched-Capacitor  
Voltage Inverters with Shutdown  
ABSOLUTE MAXIMUM RATINGS  
IN to GND.................................................................-0.3V to +6V  
OUT to GND .............................................................-6V to +0.3V  
Continuous Power Dissipation (T = +70°C)  
A
6-Pin SOT23 (derate 8.7mW/°C above +70°C).................696mW  
Operating Temperature Range ...........................-40°C to +85°C  
Junction Temperature......................................................+150°C  
Storage Temperature Range.............................-65°C to +150°C  
Lead Temperature (soldering, 10s) .................................+300°C  
C1+, SHDN, SHDN to GND.........................-0.3V to (V + 0.3V)  
IN  
C1- to GND...............................................(V  
- 0.3V) to +0.3V  
OUT  
OUT Output Current..........................................................100mA  
OUT Short Circuit to GND..............................................Indefinite  
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional  
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to  
absolute maximum rating conditions for extended periods may affect device reliability.  
ELECTRICAL CHARACTERISTICS  
(V = +5V, SHDN = GND (MAX1719), SHDN = IN (MAX1720/MAX1721), C1 = C2 = 10µF (MAX1720), C1 = C2 = 1µF  
IN  
(MAX1719/MAX1721), circuit of Figure 1, T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)  
A
A
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
1.25  
1.5  
TYP  
MAX  
5.5  
5.5  
5.5  
5.5  
90  
UNITS  
T
A
T
A
T
A
T
A
= +25°C  
MAX1720  
R = 10kΩ  
L
= 0°C to + 85°C  
= +25°C  
Supply Voltage Range  
V
V
IN  
1.4  
MAX1719/MAX1721  
R = 10kΩ  
L
= 0°C to + 85°C  
1.5  
MAX1720  
50  
Quiescent Supply Current  
(Note 3)  
I
T
A
= +25°C  
µA  
µA  
CC  
MAX1719/MAX1721  
350  
650  
SHDN = IN (MAX1719),  
SHDN = GND  
(MAX1720/MAX1721)  
T
= +25°C  
= +85°C  
0.001  
0.02  
1
A
A
Shutdown Supply Current  
I
SHDN  
T
MAX1720  
7
12  
125  
99.9  
23  
17  
Oscillator Frequency  
f
T
= +25°C  
A
kHz  
%
OSC  
MAX1719/MAX1721  
70  
99  
180  
Voltage Conversion Efficiency  
Output Resistance (Note 1)  
I
= 0, T = +25°C  
OUT  
OUT  
A
T
T
= +25°C  
50  
65  
A
R
I
= 10mA  
O
= 0°C to +85°C  
A
SHDN = IN (MAX1719), SHDN = GND  
(MAX1720/MAX1721), OUT is internally  
forced to GND in shutdown  
OUT to GND  
Shutdown Resistance  
R ,  
O SHDN  
4
12  
+2.5V V +5.5V  
2.0  
IN  
V
V
SHDN/ SHDN Input Logic High  
SHDN/ SHDN Input Logic Low  
SHDN/ SHDN Bias Current  
IH  
V
V +2.5V  
V
- 0.2  
IN (MIN)  
IN  
IN  
+2.5V V +5.5V  
0.6  
0.2  
IN  
V
V
IL  
V
V +2.5V  
IN  
IN (MIN)  
T
T
= +25°C  
= +85°C  
-100  
0.05  
10  
100  
A
SHDN/ SHDN = GND  
I , I  
IL IH  
nA  
µs  
or V  
IN  
A
MAX1720  
800  
80  
Wake-Up Time from Shutdown  
I
= 5mA  
OUT  
MAX1719/MAX1721  
2
_______________________________________________________________________________________  
SOT23, Switched-Capacitor  
Voltage Inverters with Shutdown  
ELECTRICAL CHARACTERISTICS  
(V = +5V, SHDN = GND (MAX1719), SHDN = IN (MAX1720/MAX1721), C1 = C2 = 10µF (MAX1720), C1 = C2 = 1µF  
IN  
(MAX1719/MAX1721), circuit of Figure 1, T = -40°C to +85°C, unless otherwise noted.) (Note 2)  
A
PARAMETER  
SYMBOL  
CONDITIONS  
MAX1720  
MAX1719/MAX1721  
MIN  
1.5  
TYP  
MAX  
5.5  
UNITS  
Supply Voltage Range  
V
R = 10kΩ  
L
V
IN  
1.6  
5.5  
MAX1720  
100  
750  
21  
Quiescent Current (Note 3)  
Oscillator Frequency  
I
µA  
CC  
MAX1719/MAX1721  
MAX1720  
6
f
kHz  
OSC  
MAX1719/MAX1721  
60  
99  
200  
Voltage Conversion Efficiency  
Output Resistance (Note 1)  
Output Current  
I
= 0  
%
OUT  
OUT  
R
I
= 10mA  
65  
25  
O
I
Continuous, long-term  
mA  
RMS  
OUT  
SHDN = IN (MAX1719), SHDN = GND  
(MAX1720/MAX1721), OUT is internally  
forced to GND in shutdown  
OUT to GND Shutdown  
Resistance  
R ,  
O SHDN  
12  
+2.5V V +5.5V  
2.1  
IN  
V
V
V
SHDN/ SHDN Input Logic High  
SHDN/ SHDN Input Logic Low  
IH  
V
V +2.5V  
V
- 0.2  
IN (MIN)  
IN  
IN  
+2.5V V +5.5V  
0.6  
0.2  
IN  
V
IL  
V
V +2.5V  
IN  
IN (MIN)  
Note 1: Capacitor contribution (ESR component plus (1/f  
) · C) is approximately 20% of output impedance.  
OSC  
Note 2: All specifications from -40°C to +85°C are guaranteed by design, not production tested.  
Note 3: The MAX1719/MAX1720/MAX1721 may draw high supply current during startup, up to the minimum operating supply voltage.  
To guarantee proper startup, the input supply must be capable of delivering 90mA more than the maximum load current.  
Typical Operating Characteristics  
(Circuit of Figure 1, V = +5V, SHDN = GND (MAX1719), SHDN = IN (MAX1720/MAX1721), C1 = C2 = C3, T = +25°C, unless other-  
IN  
A
wise noted.)  
OUTPUT VOLTAGE  
vs. OUTPUT CURRENT  
MAX1720  
EFFICIENCY vs. OUTPUT CURRENT  
MAX1719/MAX1721  
EFFICIENCY vs. OUTPUT CURRENT  
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
0
-1  
-2  
-3  
-4  
-5  
V
= +2V  
IN  
V
= +1.5V  
= +3.3V  
IN  
V
= +5V  
V
= +5V  
IN  
IN  
V
= +3.3V  
V
= +1.5V  
IN  
IN  
V
= +3.3V  
IN  
V
= +1.5V  
V = +2V  
IN  
IN  
V
= +2V  
IN  
V
IN  
V
= +5V  
IN  
0
5
10 15 20 25 30 35 40 45 50  
OUTPUT CURRENT (mA)  
0
5
10 15 20 25 30 35 40 45 50  
OUTPUT CURRENT (mA)  
0
5
10 15 20 25 30 35 40 45 50  
OUTPUT CURRENT (mA)  
_______________________________________________________________________________________  
3
SOT23, Switched-Capacitor  
Voltage Inverters with Shutdown  
Typical Operating Characteristics (continued)  
(Circuit of Figure 1, V = +5V, SHDN = GND (MAX1719), SHDN = IN (MAX1720/MAX1721), C1 = C2 = C3, T = +25°C, unless oth-  
IN  
A
erwise noted.)  
SUPPLY CURRENT  
vs. INPUT VOLTAGE  
OUTPUT RESISTANCE  
vs. INPUT VOLTAGE  
SHUTDOWN SUPPLY CURRENT  
vs. TEMPERATURE  
80  
70  
60  
50  
40  
30  
20  
10  
30  
25  
20  
15  
10  
5
450  
400  
350  
300  
250  
200  
150  
100  
50  
MAX1719/  
MAX1721  
V
= +5V  
IN  
MAX1719/  
MAX1721  
-40°C  
-40°C  
+85°C  
V
V
= +3.3V  
= +1.5V  
IN  
IN  
MAX1720  
MAX1720  
+85°C  
0
0
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5  
INPUT VOLTAGE (V)  
-40  
-15  
10  
35  
60  
85  
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5  
TEMPERATURE (°C)  
INPUT VOLTAGE (V)  
PUMP FREQUENCY  
vs. TEMPERATURE  
OUTPUT RESISTANCE  
vs. TEMPERATURE  
OUTPUT NOISE AND RIPPLE  
MAX1720/21toc09  
1000  
100  
10  
70  
V
V
= +1.5V  
IN  
60  
50  
40  
30  
20  
10  
V
OUT  
MAX1719/  
MAX1721  
V
= +1.5V  
IN  
V
IN  
V
= +2V  
IN  
V
= +5V  
IN  
MAX1719/MAX1721  
= +3.3V  
V
OUT  
MAX1720  
V
= +5V  
IN  
= +5V  
60  
IN  
V
= +1.5V  
-10  
IN  
MAX1720  
10µs/div  
= -3.17V, I = 5mA  
OUT  
-40  
-15  
35  
60  
85  
-40  
-15  
10  
35  
85  
V
= 3.3V, V  
IN  
OUT  
TEMPERATURE (°C)  
TEMPERATURE (°C)  
20mV/div, AC-COUPLED  
MAX1720  
OUTPUT VOLTAGE RIPPLE  
vs. CAPACITANCE  
MAX1720  
OUTPUT CURRENT vs. CAPACITANCE  
MAX1720  
START-UP FROM SHUTDOWN  
MAX1720/21toc10  
500  
450  
400  
350  
300  
250  
200  
150  
100  
50  
35  
30  
25  
20  
15  
10  
5
V
= +4.75V, V  
= -4.0V  
IN  
OUT  
V
OUT  
V
= +4.75V, V  
= -4.0V  
OUT  
IN  
2V/div  
V
= +3.15V, V  
= -2.5V  
IN  
OUT  
V
= +3.15V, V  
= -2.5V  
OUT  
IN  
V
= +1.9V, V  
= -1.5V  
IN  
OUT  
V
= +1.9V, V  
= -1.5V  
IN  
OUT  
V
SHDN  
5V/div  
0
0
0
5
10 15 20 25 30 35 40 45 50  
0
5
10  
15  
20  
25  
30  
500µs/div  
R = 1kΩ  
L
CAPACITANCE (µF)  
CAPACITANCE (µF)  
4
_______________________________________________________________________________________  
SOT23, Switched-Capacitor  
Voltage Inverters with Shutdown  
Typical Operating Characteristics (continued)  
(Circuit of Figure 1, V = +5V, SHDN = GND (MAX1719), SHDN = IN (MAX1720/MAX1721), C1 = C2 = C3, T = +25°C, unless  
IN  
A
otherwise noted.)  
MAX1719/MAX1721  
OUTPUT VOLTAGE RIPPLE vs. CAPACITANCE  
MAX1721  
START-UP FROM SHUTDOWN  
MAX1719/MAX1721  
OUTPUT CURRENT vs. CAPACITANCE  
MAX1720/21toc13  
400  
35  
30  
25  
20  
15  
10  
5
350  
300  
250  
200  
150  
100  
50  
V
V
= +4.75V, V  
= +3.15V, V  
= -4.0V  
= -2.5V  
IN  
IN  
OUT  
OUT  
V
OUT  
V
= +4.75V, V  
= -4.0V  
= -2.5V  
IN  
OUT  
2V/div  
V
= +3.15V, V  
OUT  
IN  
V
= +1.9V, V  
= -1.5V  
OUT  
IN  
V
= +1.9V, V  
= -1.5V  
IN  
OUT  
V
SHDN  
5V/div  
0
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0  
50µs/div  
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0  
CAPACITANCE (µF)  
R = 1kΩ  
L
CAPACITANCE (µF)  
Pin Description  
PIN  
NAME  
FUNCTION  
MAX1720  
MAX1721  
MAX1719  
OUT  
IN  
Inverting Charge-Pump Output  
1
2
3
4
1
2
3
4
Power-Supply Positive Voltage Input  
C1-  
GND  
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.  
5
SHDN  
Inverting Shutdown Input. Drive this pin high for normal operation; drive it low for  
shutdown mode. OUT is actively pulled to ground during shutdown.  
5
6
SHDN  
6
C1+  
Positive Terminal of Flying Capacitor  
cycle, S1 and S3 open, S2 and S4 close, and C1 is level  
Detailed Description  
shifted downward by V volts. This connects C1 in par-  
IN  
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).  
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  
IN  
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-  
than -V , since switches S1–S4 have resistance and the  
IN  
load drains charge from C2.  
_______________________________________________________________________________________  
5
SOT23, Switched-Capacitor  
Voltage Inverters with Shutdown  
f
C1  
1µF (10µF)  
V+  
V
OUT  
6
C1+  
3
C1-  
INPUT  
1.5V to 5.5V  
NEGATIVE  
OUTPUT  
2
5
1
C1  
C2  
R
L
IN  
OUT  
-1 · V  
IN  
C3  
25mA  
C2  
1µF (10µF)  
R
L
1µF (10µF)  
MAX1719*  
MAX1721  
ON  
OFF  
SHDN  
Figure 3a. Switched-Capacitor Model  
GND  
4
R
EQUIV  
V+  
V
NOTE: ( ) CAPACITORS ARE FOR MAX1720.  
OUT  
*ON/OFF POLARITY OF SHDN IS REVERSED FOR MAX1719.  
1
R
=
EQUIV  
f × C1  
C2  
R
L
Figure 1. Typical Application Circuit  
S1  
S2  
IN  
Figure 3b. Equivalent Circuit  
C1  
where the output impedance is roughly approximated  
by:  
C2  
S3  
S4  
1
V
= -(V )  
IN  
OUT  
R
+ 2R  
+ 4ESR + ESR  
SW C1 C2  
OUT  
f
(
× C1  
)
OSC  
The first term is the effective resistance of an ideal  
switched-capacitor circuit (Figures 3a and 3b), and  
SW  
Figure 2. Ideal Voltage Inverter  
R
is the sum of the charge pump’s internal switch  
resistances (typically 8to 9at V = +5V). The typi-  
IN  
Charge-Pump Output  
cal output impedance is more accurately determined  
The MAX1719/MAX1720/MAX1721 are not voltage reg-  
ulators: the charge pumps’ output resistance is  
approximately 23at room temperature (with V  
from the Typical Operating Characteristics.  
=
IN  
Shutdown Mode  
+5V), and V  
OUT  
The droop of the negative supply (V  
current draw from OUT (I  
verter’s output resistance (R ):  
approaches -5V when lightly loaded.  
OUT  
The MAX1719/MAX1720/MAX1721 have a logic-con-  
trolled shutdown input. Driving SHDN low places the  
MAX1720/MAX1721 in a low-power shutdown mode.  
The MAX1719’s shutdown input is inverted from that of  
the MAX1720/MAX1721. Driving SHDN high places the  
MAX1719 in a low-power shutdown mode. The charge-  
pump switching halts, supply current is reduced to  
1nA, and OUT is actively pulled to ground through a 4Ω  
resistance.  
V
will droop toward GND as load current increases.  
) equals the  
DROOP-  
) times the negative con-  
OUT  
O
V
= I  
x R  
OUT  
O
DROOP-  
The negative output voltage will be:  
= -(V - V )  
DROOP-  
V
OUT  
IN  
Efficiency Considerations  
The efficiency of the MAX1719/MAX1720/MAX1721 is  
dominated by its quiescent supply current (I ) at low  
Applications Information  
Capacitor Selection  
To maintain the lowest output resistance, use capaci-  
tors with low ESR (Table 1). The charge-pump output  
resistance is a function of C1’s and C2’s ESR.  
Therefore, minimizing the charge-pump capacitor’s  
ESR minimizes the total output resistance. Table 2  
gives suggested capacitor values for minimizing output  
resistance or minimizing capacitor size.  
Q
output current and by its output impedance (R  
higher output current; it is given by:  
) at  
OUT  
I
I
× R  
OUT  
OUT  
OUT  
η ≅  
1−  
I
+I  
V
OUT  
Q
IN  
6
_______________________________________________________________________________________  
SOT23, Switched-Capacitor  
Voltage Inverters with Shutdown  
Flying Capacitor (C1)  
Increasing the flying capacitor’s value reduces the out-  
IN  
+V  
2
1
2
1
put resistance. Above a certain point, increasing C1’s  
capacitance has a negligible effect because the output  
resistance becomes dominated by the internal switch  
resistance and capacitor ESR.  
3
4
3
4
MAX1719  
MAX1720  
MAX1721  
“1”  
MAX1719  
MAX1720  
MAX1721  
“n”  
C1  
C1  
V
OUT  
6
6
Output Capacitor (C2)  
Increasing the output capacitor’s value reduces the  
output ripple voltage. Decreasing its ESR reduces both  
output resistance and ripple. Lower capacitance values  
can be used with light loads if higher output ripple can  
be tolerated. Use the following equation to calculate the  
peak-to-peak ripple:  
C2  
5
5
C2  
SHDN (MAX1719)  
SHDN (MAX1720/  
MAX1721)  
V
= -nV  
IN  
OUT  
Figure 4. Cascading MAX1719s or MAX1720s or MAX1721s  
to Increase Output Voltage  
I
OUT  
V
=
+2 × I  
× ESR  
RIPPLE  
OUT C2  
2 × f  
× C2  
OSC  
Cascading Devices  
Two devices can be cascaded to produce an even  
larger negative voltage (Figure 4). The unloaded output  
Input Bypass Capacitor (C3)  
Bypass the incoming supply to reduce its AC impedance  
and the impact of the MAX1719/MAX1720/MAX1721’s  
switching noise. A bypass capacitor with a value equal  
to that of C1 is recommended.  
voltage is normally -2 x V , but this is reduced slightly  
IN  
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.  
The maximum load current and startup current of the  
nth cascaded circuit must not exceed the maximum  
output current capability of the (n - 1)th circuit to ensure  
proper startup.  
Voltage Inverter  
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.  
Table 1. Low-ESR Capacitor Manufacturers  
PRODUCTION  
MANUFACTURER  
SERIES  
PHONE  
FAX  
METHOD  
AVX  
Matsuo  
Sprague  
AVX  
TPS series  
267 series  
593D, 595D series  
X7R  
803-946-0690  
714-969-2491  
603-224-1961  
803-946-0690  
714-969-2491  
803-626-3123  
714-960-6492  
603-224-1430  
803-626-3123  
714-960-6492  
Surface-Mount  
Tantalum  
Surface-Mount  
Ceramic  
Matsuo  
X7R  
Table 2. Capacitor Selection for Minimum Output Resistance or Capacitor Size  
CAPACITORS TO MINIMIZE  
OUTPUT RESISTANCE  
CAPACITORS TO MINIMIZE SIZE  
PART  
f
(R = 40, TYP)  
OSC  
O
(R = 23, TYP)  
O
C1 = C2  
C1 = C2  
MAX1720  
12kHz  
10µF  
3.3µF  
MAX1719/MAX1721  
125kHz  
1µF  
0.33µF  
_______________________________________________________________________________________  
7
SOT23, Switched-Capacitor  
Voltage Inverters with Shutdown  
SHDN (MAX1719)  
SHDN (MAX1720)  
+V  
IN  
(MAX1721)  
+V  
IN  
2
1
2
1
5
3
2
1
D1, D2 = 1N4148  
3
4
6
3
4
6
MAX1719  
MAX1720  
MAX1721  
“1”  
MAX1719  
MAX1720  
MAX1721  
“n”  
C1  
4
6
C1  
MAX1719  
MAX1720  
MAX1721  
C1  
D1  
D2  
V
OUT  
V
= -V  
IN  
OUT  
5
C2  
C4  
5
SHDN (MAX1719)  
SHDN (MAX1720/  
MAX1721)  
C2  
V
= -V  
V
= (2V ) -  
IN  
OUT  
IN  
OUT  
(V ) - (V  
)
FD2  
FD1  
R
OF SINGLE DEVICE  
NUMBER OF DEVICES  
O
C3  
R
=
O
Figure 5. Paralleling MAX1719s or MAX1720s or MAX1721s to  
Reduce Output Resistance  
Figure 6. Combined Doubler and Inverter  
Paralleling Devices  
Paralleling multiple MAX1719s, MAX1720s, or  
MAX1721s reduces the output resistance. 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 calcu-  
lating output resistance.  
4
V+  
GND  
MAX1719  
MAX1720  
MAX1721  
R
L
1
OUT  
Figure 7. Heavy Load Connected to a Positive Supply  
Combined Doubler/Inverter  
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 25mA.  
OUT require a Schottky diode (1N5817) between GND  
and OUT, with the anode connected to OUT (Figure 7).  
Layout and Grounding  
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.  
Heavy Load Connected to a  
Positive Supply  
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  
Chip Information  
TRANSISTOR COUNT: 85  
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are  
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.  
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600  
© 2004 Maxim Integrated Products  
Printed USA  
is a registered trademark of Maxim Integrated Products.  

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