Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
Advanced
AMS682
Monolithic
INVERTING VOLTAGE DOUBLER
Systems
FEATURES
APPLICATIONS
·
·
99.9% Voltage Conversion Efficiency
·
·
Portable Handheld Instrumentation
·
·
92% Power Conversion Efficiency
·
·
Cellular Phones
·
·
Wide Input Voltage Range +2.4V to 5.5V
·
·
Panel Meters
·
·
185
µ
µ
A Supply Current
·
·
-10V from +5V logic Supply
·
·
Available in SO-8 and PDIP Packages
·
·
-6V from a Single 3V Lithium Cell
·
·
Only 3 external Capacitors Required
·
·
LCD Display Bias Generator
·
·
Operational Amplifiers Power Supplies
GENERAL DESCRIPTION
The AMS682 is a CMOS charge pump converter that provides an inverted doubled output from a single positive supply.
Requiring only three external capacitors for full circuit implementation the device has an on -board 12kHz (typical) oscillator
which provides the clock.
Low output source impedance (typically 140
), provides output current up to 10mA. The AMS682 features low quiescent
current and high efficiency, making it the ideal choice for a wide variety of applications that require a negative voltage
derived from a single positive supply. The compact size and minimum external parts count of the AMS682 makes it useful in
many medium current, dual voltage analog power supplies.
The AMS682E is operational in the full industrial temperature range of -40
°
C to 85
°
C while AMS682C is operating over a
0
°
C to 70
°
C temperature range. The AMS682E/AMS682C are available in surface mount 8-Pin SOIC (SO-8) and 8-Pin
Plastic DIP (PDIP) packages.
ORDERING INFORMATION:
PACKAGE TYPE
OPERATING
8 LEAD SOIC
8 LEAD PDIP
TEMPERATURE RANGE
AMS682ES
AMS682EP
-40 to 85
°
C
AMS682CS
AMS682CP
0 to 70
°
C
TYPICAL OPERATING CIRCUIT PIN CONFIGURATIONS
V
IN
V
OUT
GND
All Caps = 3.3
µ
F
V
OUT
= -(2 X V
IN
)
+2.4V < V
IN
< +5.5V
C
2
C
1
C
OUT
+
+
-
-
+
V
IN
V
OUT
GND
C
1
+
C
2
+
C
1
-
C
2
-
ON/OFF
8-LEAD DIP/ 8-LEAD SOIC
AMS682
1
4
3
2
8
7
6
5
ON/OFF
C
+
1
V
IN
GND
V
OUT
C
-
2
C
+
2
C
-
2
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS682
ABSOLUTE MAXIMUM RATINGS
V
IN
+5.8V
Operating Temperature Range
V
IN
V/
T
1V/
µ
sec
AMS682E
-40
°
C to 85
°
C
V
OUT
-11.6V
AMS682C
0
°
C to 70
°
C
V
OUT
Short Circuit Duration
Continuous
Storage temperature
-85
°
C to +150
°
C
Power Dissipation (T
A
70
°
C)
Soldering information
Plastic DIP
730mW
Lead Temperature (Soldering 10sec)
+300
°
C
SOIC
470mW
ELECTRICAL CHARACTERISTICS
Electrical Characteristics at V
IN
=+5V and T
A
= +25°C test circuit figure 1, unless otherwise specified.
Parameter
Conditions
AMS682
Min Typ Max
Units
Supply Voltage Range
V
IN
R
L
=2k
2.4
5.5
V
Supply Current
I
IN
R
L
=
R
L
=
185
300
400
µ
A
V
OUT
Source Resistance
Source Resistance
R
OUT
I
-
L
=
10mA
I
-
L
=10mA
I
-
L
= 5mA , V
IN
= 2.8V
140
170
180
230
320
Oscillator Frequency
F
OSC
12
kHz
Power Efficiency
P
EFF
R
L
= 2k
90
92
%
Voltage Conversion Efficiency
V
OUT
E
FF
V
OUT
R
L
=
99
99.9
%
PIN DESCRIPTION
PIN NO
8-PIN DIP/SOIC
SYMBOL
DESCRIPTION
1
C
1
-
Input. Capacitor C
1
negative
terminal.
2
C
2
+
Input. Capacitor C
2
positive
terminal.
3
C
2
-
Input. Capacitor C
2
negative
terminal
4
V
OUT
Output. Negative output voltage
(-2V
IN
)
5
GND
Input. Device ground.
6
V
IN
Input. Power supply voltage.
7
C
1
+
Input. Capacitor C
1
positive
terminal.
8
ON/OFF
ON/OFF Oscilator.
V
IN
(+5V)
V
-
OUT
GND
All Caps = 3.3
µ
F
4
2
3
1
C
1
-
C
2
+
C
2
-
V-
OUT
C
1
+
V
IN
ON/OFF
GND
5
7
8
6
C
OUT
+
-
R
L
C
2
C
1
+
-
-
+
Figure 1. AMS682 Test Circuit
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS682
DETAILED DESCRIPTION
Phase 1
V
SS
charge storage- before this phase of the clock cycle,
capacitor C
1
is already charged to +5V. C
1
+
is then switched
to ground and the charge in C
1
-
is transferred to C
2
-
.
Since C
2
+
is at +5V, the voltage potential across capacitor C
2
is now -10V.
-
+
C
3
+
-
C1 C2
SW2
-5V
SW4
SW3
SW1
V
IN
=+5V
V
OUT
+
-
Figure 2. Charge Pump - Phase 1
Phase 2
V
SS
transfer- phase two of the clock connects the negative
terminal of C
2
to the negative side of reservoir capacitor C
3
and the positive terminal of C
2
to the ground, transferring the
generated -10V to C
3
. Simultaneously, the positive side of
capacitor C
1
is switched to +5V and the negative side is
connected to ground. C
2
is then switched to V
CC
and GND and
Phase 1 begins again.
-
+
C
3
+
-
C1 C2
SW2
-10V
SW4
SW3
SW1
V
IN
=+5V
V
OUT
+
-
Figure 3. Charge Pump - Phase 2
MAXIMUM OPERATING LIMITS
The AMS682 has on-chip zener diodes that clamp VIN to
approximately 5.8V, and V
-
OUT
to -11.6V. Exceeding the
maximum supply voltage will potentially damage the chip.
With an input voltage of 2V to 5.5V the AMS682 will operate
over the entire operating temperature range.
EFFICIENCY CONSIDERATIONS
Theoretically a charge pump voltage multiplier can approach
100% efficiency under the following conditions:
·
The charge pump switches have virtually no offset and are
extremely low on resistance.
·
Minimal power is consumed by the drive circuitry.
·
The Impedances of the reservoir and pump capacitors are
negligible.
For the AMS682, efficiency is as shown below:
Voltage Efficiency = V
OUT
/ (-2V
IN
)
V
OUT
= -2V
IN
+ V
DROP
V
DROP
= (I
OUT
) (R
OUT
)
Power Loss = I
OUT
(V
DROP
)
There will be a substantial voltage difference between V
OUT
and
2V
IN
if the impedances of the pump capacitors C
1
and C
2
are
high with respect to their respective output loads.
If the values of the reservoir capacitor C
3
are larger the output
ripple will be reduced. The efficiency will be improved if both
pump and reservoir capacitors have larger values. ( See
"Capacitor Selection" in Application Section.)
APPLICATIONS
Negative Doubling Converter
The AMS682 is most commonly used as a charge pump voltage
converter which provides a negative output of two times a
positive input voltage (Fig.4)
GND
V
IN
6
4
V
-
OUT
5
7
2
3
1
C
1
-
C
2
+
C
1
+
C
2
-
GND
V
IN
V-
OUT
C
3
22
µ
F
+
+
+
22
µ
F
22
µ
F
C
1
C
2
ON/OFF
8
Figure 4. Inverting Voltage Doubler
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS682
APPLICATIONS
(Continued)
Capacitor Selection
The output resistance of the AMS682 is determined in part by
the ESR of the capacitors used. An expression for R
OUT
is
derived as shown below:
R
OUT
= 2( R
SW1
+R
SW2
+ESR
C1
+ R
SW3
+R
SW4
+ESR
C2
)
+2(R
SW1
+R
SW2
+ESR
C1
+ R
SW3
+R
SW4
+ESR
C2
)
+1/ (f
PUMP
X C1) +1/ (f
PUMP
X C2) + ESR
C3
Assuming all switch resistances are approximately equal:
R
OUT
= 16 R
SW
+ 4ESR
C1
+ 4ESR
C2
+ ESR
C3
+1/ (f
PUMP
X C1) +1/ (f
PUMP
X C2)
R
OUT
is typically 140
at +25
°
C with VIN =+5V and 3.3
µ
F
low ESR capacitors. The fixed term (16RSW) is about 80-
90
. Increasing or decreasing values of C1 and C2 will affect
efficiency by changing R
OUT
.
Table 1 shows R
OUT
for various values of C1 and C2 (assume
0.5
ESR). C1 must be rated at 6VDC or greater while C2
and C3 must be rated at 12VDC or greater.
Output voltage ripple is affected by C3. Typically the larger
the value of C3 the less the ripple for a given load current.
The formula for p-p V
RIPPLE
is :
V
RIPPLE
= [1/[2(f
PUMP
X C3)]+2(ESR
C3
)] (I
OUT
)
For a 10
µ
F (0.5
ESR), f
PUMP
= 10kHz and I
OUT
=10mA the
peak -to-peak ripple voltage at the output will be less than
60mV. In most applications (I
OUT
10mA) a 10-20
µ
F
capacitor and 1-5
µ
F pump capacitors will be sufficient. Table
2 shows V
RIPPLE
for different values of C3 (assume 1
ESR).
Paralleling devices
Paralleling multiple AMS682 reduces the output resistance of
the converter. The effective output resistance is the output
resistance of one device divided by the number of devices.
Figure 5 illustrates how each device requires separate pump
capacitors C
1
and C
2
, but all can share a single reservoir
capacitor.
-5V Regulated Supply From A Single 3V Battery
Figure 6 shows a -5V power supply using one 3V battery.
The AMS682 provides -6V at V
-
OUT
, which is regulated to -5V
by the negative LDO. The AMS682 input can vary from 3V to
5.5V without affecting regulation significantly. A voltage
detector is connected to the battery to detect undervoltage.
This unit is set to detect at 2.7V. With higher input voltage,
more current can be drawn from the outputs of the AMS682.
With 5V at V
IN
, 10mA can be drawn from the regulated
output. Assuming 150
source resistance for the converter,
with I
L
=10mA, the charge pump will drop 1.5V.
Table 1. R
OUT
vs. C1, C2
Table 2. V
RIPPLE
Peak-to-Peak vs. C3 (I
OUT
=10mA)
C1, C2 (
µ
µ
F)
R
OUT
(
)
C3(
µ
µ
F)
V
RIPPLE
(mV)
0.05
4085
0.50
1020
0.10
2084
1.00
520
0.47
510
3.30
172
1.00
285
5.00
120
3.30
145
10.00
70
5.00
125
22.00
43
10.00
105
100.00
25
22.00
94
100.00
87
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS682
APPLICATIONS
(Continued)
VIN
C1+
C1-
C2+
C2-
GND
VIN
C1+
C1-
C2+
C2-
GND
GND
V
IN
NEGATIVE
SUPPLY
+
+
-
-
+
+
-
-
10
µ
F
10
µ
F
10
µ
F
10
µ
F
V
-
OUT
V
-
OUT
+
-
C
-
OUT
22
µ
F
Figure 5. Paralleling AMS682 for Lower Output Source Resistance
VIN
C1+
C1-
C2+
C2- V
-
OUT
GND
+
10
µ
F
+ -
+
V
SS
V
IN
V
OUT
NEG. LDO
VOLTAGE
DETECT.
V
IN
V
OUT
V
SS
- 22
µ
F
+ C
-
OUT
- 10
µ
F
-
GROUND
-5 SUPPLY
+
- 1
µ
F
LOW BATTERY
3V
Figure 6. Negative Supply Derived from 3V Battery
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS682
TYPICAL PERFORMANCE CHARACTERISTICS
(F
OSC
= 12kHz)
V
IN
= 5V
V
IN
= 5V
I
OUT
= 10mA
NO LOAD
V
IN
= 5V
C3 = 10
µ
F
-7.5
-8.0
-8.5
-9.0
-9.5
-10.0
-10.5
0
5
10
15
240
220
180
160
140
120
1
2
3
4
5
6
V
OUT
vs. Load Current
Output Resistance vs. V
IN
200
OUTPUT RESISTANCE
(
)
V
OUT
(V)
V
IN
(V)
LOAD CURRENT
200
180
160
140
120
100
80
-50
0
50
100
1
2
3
4
6
5
300
250
200
150
100
50
SUPPLY CURRENT (
µ
A)
V
IN
(V)
OUTPUT SOURCE RESISTANCE (
)
Output Source Resistance vs. Temperature
TEMPERATURE (°C)
200
150
100
50
0
0
5
10
15
20
OUTPUT CURRENT (mA)
Output Ripple vs. Output Current
OUTPUT RIPPLE (mV PK-PK)
Supply Current vs. V
IN
C1-C3 = 3.3
µ
F
C3 = 100
µ
F
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS682
PACKAGE DIMENSIONS inches (millimeters) unless otherwise noted.
8 LEAD SOIC PLASTIC PACKAGE (S)
8 LEAD PLASTIC DIP PACKAGE (P)
0°-8° TYP
0.010-0.020
(0.254-0.508)
S (SO-8 ) AMS DRW# 042293
x 45°
0.016-0.050
(0.406-1.270)
0.008-0.010
(0.203-0.254)
0.004-0.010
(0.101-0.254)
0.014-0.019
(0.355-0.483)
0.053-0.069
(1.346-1.752)
0.050
(1.270)
TYP
0.150-0.157**
(3.810-3.988)
0.228-0.244
(5.791-6.197)
0.189-0.197*
(4.801-5.004)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
1
2
3
4
8
7
6
5
0.045-0.065
(1.143-1.651)
0.255±0.015*
(6.477±0.381)
0.400*
(10.160)
MAX
1
2
3
4
8
7
6
5
0.130±0.005
(3.302±0.127)
0.018±0.003
(0.457±0.076)
0.100±0.010
(2.540±0.254)
(
8.255
)
+0.635
-0.381
0.325 +0.025
-0.015
0.009-0.015
(0.229-0.381)
0.300-0.325
(7.620-8.255)
0.065
(1.651)
TYP
0.005
(0.127)
MIN
0.125
(3.175)
MIN
0.015
(0.380)
MIN
*DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTUSIONS.
MOLD FLASH OR PROTUSIONS SHALL NOT EXCEED 0.010" (0.254mm)
P (8L PDIP ) AMS DRW# 042294
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