MAX1720EUT+T [MAXIM]
Switched Capacitor Converter, 0.025A, 21kHz Switching Freq-Max, CMOS, PDSO6, SOT-23, 6 PIN;
| 型号： | MAX1720EUT+T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Switched Capacitor Converter, 0.025A, 21kHz Switching Freq-Max, CMOS, PDSO6, SOT-23, 6 PIN |
| 文件： | 总8页 (文件大小：124K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1439; Rev 1; 5/99
S OT2 3 , S w it c h e d -Ca p a c it o r
Vo lt a g e In ve rt e rs w it h S h u t d o w n
90/MAX721
Ge n e ra l De s c rip t io n
Fe a t u re s
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 (MAX1719/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
inve rte rs without s hutd own (5-p in SOT23), s e e the
MAX828/MAX829 and MAX870/MAX871 data sheets. For
applications requiring more power, the MAX860/MAX861
Ord e rin g In fo rm a t io n
deliver up to 50mA. For regulated outputs (up to -2 · 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
Ap p lic a t io n s
Local Negative Supply from a Positive Supply
Small LCD Panels
GaAs PA Bias Supply
Handy-Terminals, PDAs
Battery-Operated Equipment
P in Co n fig u ra t io n
Typ ic a l Op e ra t in g Circ u it
1µF
TOP VIEW
C1+
C1-
OUT
OUT
IN
1
2
3
C1+
6
5
4
NEGATIVE
OUTPUT
INPUT
1.5V to 5.5V
IN
-1 · V
IN
MAX1719
MAX1720
MAX1721
25mA
SHDN (SHDN)
GND
MAX1721
GND
1µF
C1-
SHDN
ON
OFF
SOT23-6
( ) ARE FOR MAX1719
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
S OT2 3 , S w it c h e d -Ca p a c it o r
Vo lt a g e In ve rt e rs w it h S h u t d o w n
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, 10sec) .............................+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 = -40°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
= +25°C
MAX1720
= 10kΩ
R
L
T
= 0°C to + 85°C
= +25°C
A
Supply Voltage Range
V
IN
V
T
A
1.4
MAX1719/MAX1721
R
= 10kΩ
L
T
A
= 0°C to + 85°C
1.5
MAX1720
50
Quiescent Supply Current
Shutdown Supply Current
I
CC
T
A
= +25°C
µA
µA
MAX1719/MAX1721
350
650
SHDN = IN (MAX1719),
SHDN = GND
(MAX1720/MAX1721)
T
= +25°C
= +85°C
0.001
0.02
1
A
I
SHDN
T
A
MAX1720
7
12
125
99.9
23
17
Oscillator Frequency
f
T
= +25°C
kHz
%
OSC
A
90/MAX721
MAX1719/MAX1721
70
99
180
Voltage Conversion Efficiency
Output Resistance (Note 1)
I
= 0, T = +25°C
OUT
A
T
A
= +25°C
50
65
R
I
= 10mA
Ω
O
OUT
T
A
= 0°C to +85°C
SHDN = IN (MAX1719), SHDN = GND
(MAX1720/MAX1721), OUT is internally
forced to GND in shutdown
OUT to GND
Shutdown Resistance
R ,
O
4
12
Ω
SHDN
+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
IL
V
V
≤ V ≤ +2.5V
IN
IN (MIN)
T
= +25°C
= +85°C
-100
0.05
10
100
A
SHDN/ SHDN = GND
or V
I , I
IL IH
nA
µs
IN
T
A
MAX1720
800
80
Wake-Up Time from Shutdown
I
= 5mA
OUT
MAX1719/MAX1721
2
_______________________________________________________________________________________
S OT2 3 , S w it c h e d -Ca p a c it o r
Vo lt a g e In ve rt e rs w it h S h u t d o w n
90/MAX721
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
IN
R
= 10kΩ
L
V
1.6
5.5
100
750
21
Quiescent Current
I
MAX1719/MAX1720/MAX1721
µA
CC
MAX1720
6
Oscillator Frequency
f
kHz
OSC
MAX1719/MAX1721
60
99
200
Voltage Conversion Efficiency
Output Resistance (Note 1)
Output Current
I
= 0
%
OUT
R
I
= 10mA
65
25
Ω
O
OUT
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
12
Ω
SHDN
+2.5V ≤ V ≤ +5.5V
2.0
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.
Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
(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
MAX1720
MAX1719/MAX1721
vs. OUTPUT CURRENT
EFFICIENCY vs. OUTPUT CURRENT
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
IN
= +2V
V
= +1.5V
= +3.3V
IN
V
IN
= +5V
V
IN
= +5V
V
IN
= +3.3V
V
IN
= +1.5V
V
IN
= +3.3V
V
IN
= +1.5V
V = +2V
IN
V
IN
= +2V
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
S OT2 3 , S w it c h e d -Ca p a c it o r
Vo lt a g e In ve rt e rs w it h S h u t d o w n
Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(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
= +3.3V
= +1.5V
IN
MAX1720
V
IN
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
= +1.5V
IN
60
50
40
30
20
10
V
OUT
MAX1721
V
IN
= +1.5V
V
= +2V
IN
V
= +5V
IN
MAX1719/MAX1721
MAX1720
90/MAX721
V
IN
= +3.3V
V
OUT
MAX1720
V
IN
= +5V
V
= +5V
60
IN
V
IN
= +1.5V
-10
10µs/div
= 3.3V, V = -3.17V, I = 5mA
20mV/div, AC-COUPLED
-40
-15
35
60
85
-40
-15
10
35
85
V
IN
OUT
OUT
TEMPERATURE (°C)
TEMPERATURE (°C)
MAX1720
MAX1720
OUTPUT CURRENT vs. CAPACITANCE
OUTPUT VOLTAGE RIPPLE
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
OUT
IN
V
2V/div
OUT
V
IN
= +4.75V, V = -4.0V
OUT
V
IN
= +3.15V, V = -2.5V
OUT
V
IN
= +3.15V, V = -2.5V
OUT
V
IN
= +1.9V, V = -1.5V
OUT
V
= +1.9V, V = -1.5V
OUT
IN
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
_______________________________________________________________________________________
S OT2 3 , S w it c h e d -Ca p a c it o r
Vo lt a g e In ve rt e rs w it h S h u t d o w n
90/MAX721
Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(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
MAX1721
MAX1719/MAX1721
OUTPUT VOLTAGE RIPPLE vs. CAPACITANCE
400
START-UP FROM SHUTDOWN
OUTPUT CURRENT vs. CAPACITANCE
MAX1720/21toc13
35
30
25
20
15
10
5
350
300
250
200
150
100
50
V
IN
= +4.75V, V = -4.0V
OUT
V
2V/div
OUT
V
= +4.75V, V = -4.0V
OUT
IN
V
IN
= +3.15V, V = -2.5V
OUT
V
IN
= +3.15V, V = -2.5V
OUT
V
= +1.9V, V = -1.5V
OUT
IN
V
IN
= +1.9V, V = -1.5V
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)
P in De s c rip t io n
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.
–
6
5
6
SHDN
C1+
Positive Terminal of Flying Capacitor
cycle, S1 and S3 open, S2 and S4 close, and C1 is level
De t a ile d De s c rip t io n
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 volta g e a c ros s C2 re a c he s
-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
load drains charge from C2.
IN
_______________________________________________________________________________________
5
S OT2 3 , S w it c h e d -Ca p a c it o r
Vo lt a g e In ve rt e rs w it h S h u t d o w n
f
C1
1µF (10µF)
V+
V
OUT
6
3
INPUT
1.5V to 5.5V
NEGATIVE
OUTPUT
C1+
C1-
2
5
1
C1
C2
R
L
IN
OUT
-1 · V
IN
C3
1µF (10µF)
25mA
C2
1µF (10µF)
R
L
MAX1719*
MAX1721
ON
OFF
SHDN
Figure 3a. Switched-Capacitor Model
GND
4
R
EQUIV
V+
V
OUT
NOTE: ( ) CAPACITORS ARE FOR MAX1720.
*ON/OFF POLARITY OF SHDN IS REVERSED FOR MAX1719.
1
R
EQUIV
=
f × C1
C2
R
L
Figure 1. Typical Application Circuit
S1
S3
S2
IN
Figure 3b. Equivalent Circuit
C1
The internal losses are associated with the IC’s internal
functions, such as driving the switches, oscillator, etc.
These losses are affected by operating conditions such
as input voltage, temperature, and frequency.
C2
S4
V
OUT
= -(V )
IN
The other two losses are associated with the voltage
converter circuit’s output resistance. Switch losses
occur because of the on-resistance of the MOSFET
s witc he s in the IC. Cha rg e -p ump c a p a c itor los s e s
occur because of their ESR. The relationship between
these losses and the output resistance is as follows:
Figure 2. Ideal Voltage Inverter
90/MAX721
Ch a rg e -P u m p Ou t p u t
The MAX1719/MAX1720/MAX1721 are not voltage reg-
ula tors : the c ha rg e p ump s ’ outp ut re s is ta nc e is
P
+ P
PUMP CAPACITOR LOSSES
SWITCH LOSSES
2
approximately 23Ω at room temperature (with V
=
IN
= I
R
O
OUT
+5V), and V
approaches -5V when lightly loaded.
OUT
1
V
OUT
will droop toward GND as load current increases.
R
+2R
+ 4ESR +ESR
O
SWITCHES C1 C2
f
C1
The droop of the negative supply (V ) equals the
DROOP-
(
)
OSC
current draw from OUT (I ) times the negative con-
OUT
verter’s output resistance (R ):
where f
is the oscillator frequency. The first term is
O
OSC
the e ffe c tive re s is ta nc e from a n id e a l s witc he d -
capacitor circuit. See Figures 3a and 3b.
V
= I
· R
DROOP-
OUT
O
The negative output voltage will be:
= -(V - V )
DROOP-
S h u t d o w n Mo d e
V
OUT
IN
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.
Effic ie n c y Co n s id e ra t io n s
The power efficiency of a switched-capacitor voltage
converter is affected by three factors: the internal loss-
es in the converter IC, the losses in the power switches,
and the resistive losses of the pump capacitors. The
total power loss is:
ΣP
= P
+ P
LOSS
INTERNAL LOSSES
SWITCH LOSSES
PUMP CAPACITOR LOSSES
+ P
6
_______________________________________________________________________________________
S OT2 3 , S w it c h e d -Ca p a c it o r
Vo lt a g e In ve rt e rs w it h S h u t d o w n
90/MAX721
Ap p lic a t io n s In fo rm a t io n
…
+V
IN
Ca p a c it o r S e le c t io n
To maintain the lowest output resistance, use capaci-
tors with low ESR (Table 1). The charge-pump output
re s is ta nc e is a func tion of C1’s a nd C2’s ESR.
Therefore, minimizing the charge-pump capacitor’s
ESR minimize s the tota l output re sista nc e . Ta ble 2
gives suggested capacitor values for minimizing output
resistance or minimizing capacitor size.
2
1
2
1
3
4
3
4
MAX1719
MAX1720
MAX1721
“1”
MAX1719
MAX1720
MAX1721
“n”
C1
C1
V
OUT
6
6
…
C2
5
5
C2
SHDN (MAX1719)
SHDN (MAX1720/
MAX1721)
V
= -nV
IN
OUT
Flying Capacitor (C1)
Increasing the flying capacitor’s value reduces the out-
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.
Figure 4. Cascading MAX1719s or MAX1720s or MAX1721s
to Increase Output Voltage
Vo lt a g e In ve rt e r
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.
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:
Ca s c a d in g De vic e s
Two devices can be cascaded to produce an even
larger negative voltage (Figure 4). The unloaded output
IOUT
V
=
+ 2 IOUT ESRC2
RIPPLE
2 x fOSC C2
voltage is normally -2 · 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.
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.
Table 1. Low-ESR Capacitor Manufacturers
PRODUCTION
METHOD
MANUFACTURER
SERIES
PHONE
FAX
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 = 40Ω, TYP)
OSC
O
(R = 23Ω, TYP)
O
C1 = C2
C1 = C2
MAX1720
12kHz
10µF
3.3µF
MAX1719/MAX1721
125kHz
1µF
0.33µF
_______________________________________________________________________________________
7
S OT2 3 , S w it c h e d -Ca p a c it o r
Vo lt a g e In ve rt e rs w it h S h u t d o w n
SHDN (MAX1719)
SHDN (MAX1720/
…
+V
IN
MAX1721)
+V
IN
5
2
2
1
3
2
1
D1, D2 = 1N4148
3
4
6
3
4
6
MAX1719
MAX1720
MAX1721
“1”
MAX1719
MAX1720
MAX1721
“n”
C1
4
6
MAX1719
MAX1720
MAX1721
C1
C1
D1
D2
V
OUT
1
V
OUT
= -V
IN
C2
C4
5
5
SHDN (MAX1719)
SHDN (MAX1720/
MAX1721)
…
V
= (2V ) -
IN
C2
V
OUT
= -V
OUT
IN
(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
P a ra lle lin g De vic e s
Pa ra lle ling multip le 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
Co m b in e d Do u b le r/In ve rt e r
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).
90/MAX721
La yo u t a n d Gro u n d in g
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.
He a vy Lo a d Co n n e c t e d t o a
P o s it ive S u p p ly
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
Ch ip In fo rm a t io n
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
_____________________Ma x im In t e g ra t e d P ro d u c t s , 1 2 0 S a n Ga b rie l Drive , S u n n yva le , CA 9 4 0 8 6 4 0 8 -7 3 7 -7 6 0 0
© 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
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