REV. B
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ADM660/ADM8660
CMOS Switched-Capacitor
Voltage Converters
FEATURES
ADM660: Inverts or Doubles Input Supply Voltage
ADM8660: Inverts Input Supply Voltage
100 mA Output Current
Shutdown Function (ADM8660)
2.2 F or 10 F Capacitors
0.3 V Drop at 30 mA Load
+1.5 V to +7 V Supply
Low Power CMOS: 600 A Quiescent Current
Selectable Charge Pump Frequency (25 kHz/120 kHz)
Pin Compatible Upgrade for MAX660, MAX665, ICL7660
Available in 16-Lead TSSOP Package
APPLICATIONS
Handheld Instruments
Portable Computers
Remote Data Acquisition
Op Amp Power Supplies
TYPICAL CIRCUIT CONFIGURATIONS
+
+
+1.5V TO +7V
INPUT
C1
10F
C2
10F
INVERTED
NEGATIVE
OUTPUT
ADM660
FC
CAP+
GND
CAP–
V+
OSC
LV
OUT
Voltage Inverter Configuration (ADM660)
+
+
+1.5V TO +7V
INPUT
C1
10F
C2
10F
INVERTED
NEGATIVE
OUTPUT
ADM8660
FC
CAP+
GND
CAP–
V+
LV
OUT
SD
SHUTDOWN
CONTROL
Voltage Inverter Configuration with Shutdown (ADM8660)
GENERAL DESCRIPTION
The ADM660/ADM8660 is a charge-pump voltage converter
that can be used to either invert the input supply voltage giving
V
OUT
= –V
IN
or double it (ADM660 only) giving V
OUT
= 2 ⫻ V
IN
.
Input voltages ranging from +1.5 V to +7 V can be inverted into
a negative –1.5 V to –7 V output supply. This inverting scheme
is ideal for generating a negative rail in single power supply
systems. Only two small external capacitors are needed for the
charge pump. Output currents up to 50 mA with greater than
90% efficiency are achievable, while 100 mA achieves greater
than 80% efficiency.
A Frequency Control (FC) input pin is used to select either
25 kHz or 120 kHz charge-pump operation. This is used to
optimize capacitor size and quiescent current. With 25 kHz
selected, a 10 µF external capacitor is suitable, while with 120 kHz
the capacitor may be reduced to 2.2 µF. The oscillator frequency
on the ADM660 can also be controlled with an external capacitor
connected to the OSC input or by driving this input with an
external clock. In applications where a higher supply voltage is
desired it is possible to use the ADM660 to double the input
voltage. With input voltages from 2.5 V to 7 V, output voltages
from 5 V to 14 V are achievable with up to 100 mA output current.
The ADM8660 features a low power shutdown (SD) pin instead
of the external oscillator (OSC) pin. This can be used to disable
the device and reduce the quiescent current to 300 nA.
The ADM660 is a pin compatible upgrade for the MAX660,
MAX665, ICL7660, and LTC1046.
The ADM660/ADM8660 is available in 8-lead DIP and
narrow-body SOIC. The ADM660 is also available in a 16-lead
TSSOP package.
ADM660/ADM8660 Options
Option ADM660 ADM8660
Inverting Mode Y Y
Doubling Mode Y N
External Oscillator Y N
Shutdown N Y
Package Options
R-8 Y Y
N-8 Y Y
RU-16 Y N
REV. B–2–
ADM660/ADM8660–SPECIFICATIONS
Parameter Min Typ Max Unit Test Conditions/Comments
Input Voltage, V+ R
L
= 1 kW
3.5 7.0 V Inverting Mode, LV = Open
1.5 7.0 V Inverting Mode, LV = GND
2.5 7.0 V Doubling Mode, LV = OUT
Supply Current No Load
0.6 1 mA FC = Open (ADM660), GND (ADM8660)
2.5 4.5 mA FC = V+, LV = Open
Output Current 100 mA
Output Resistance (ADM660) 9 15 WI
L
= 100 mA
Output Resistance (ADM8660) 9 15 WI
L
= 100 mA, T
A
= 25∞C
Output Resistance (ADM8660) 16.5 WI
L
= 100 mA, T
A
= –40∞C to +85∞C
Charge-Pump Frequency 25 kHz FC = Open (ADM660), GND (ADM8660)
120 kHz FC = V+
OSC Input Current ±5mAFC = Open (ADM660), GND (ADM8660)
±25 mAFC = V+
Power Efficiency (FC = Open) (ADM660) 90 94 % R
L
= 1 kW Connected from V+ to OUT
Power Efficiency (FC = Open) (ADM8660) 90 94 % R
L
= 1 kW Connected from V+ to OUT,
T
A
= +25∞C
Power Efficiency (FC = Open) (ADM8660) 88.5 % R
L
= 1 kW Connected from V+ to OUT,
T
A
= –40∞C to +85∞C
Power Efficiency (FC = Open) (ADM660) 90 93 % R
L
= 500 W Connected from OUT to GND
Power Efficiency (FC = Open) (ADM8660) 90 93 % R
L
= 500 W Connected from OUT to GND,
T
A
= +25∞C
Power Efficiency (FC = Open) (ADM8660) 88.5 % R
L
= 500 W Connected from OUT to GND,
T
A
= –40∞C to +85∞C
Power Efficiency (FC = Open) 81.5 % I
L
= 100 mA to GND
Voltage Conversion Efficiency 99 99.96 % No Load
Shutdown Supply Current, I
SHDN
0.3 5 mAADM8660, SHDN = V+
Shutdown Input Voltage, V
SHDN
2.4 V SHDN High = Disabled
0.8 V SHDN Low = Enabled
Shutdown Exit Time 500 msI
L
= 100 mA
*
C1 and C2 are low ESR (<0.2 W) electrolytic capacitors.
High ESR degrade performance.
Specifications subject to change without notice.
(V+ = +5 V, C1, C2 = 10F,* TA = TMIN to TMAX, unless
otherwise noted.)
REV. B
ADM660/ADM8660
–3–
Power Dissipation, RU-16 . . . . . . . . . . . . . . . . . . . . . 500 mW
(Derate 6 mW/°C above +50°C)
θ
JA
, Thermal Impedance . . . . . . . . . . . . . . . . . . . . 158°C/W
Operating Temperature Range
Industrial (A Version) . . . . . . . . . . . . . . . . – 40°C to +85°C
Storage Temperature Range . . . . . . . . . . . –65°C to +150°C
Lead Temperature Range (Soldering 10 sec) . . . . . . . . +300°C
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . +215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . +220°C
ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >2000 V
*
This is a stress rating only; functional operation of the device at these or any other
conditions above those indicated in the operation section of this specification is not
implied. Exposure to absolute maximum rating conditions for extended periods
may affect device reliability.
ABSOLUTE MAXIMUM RATINGS*
(T
A
= +25°C, unless otherwise noted.)
Input Voltage (V+ to GND, GND to OUT) . . . . . . . . +7.5 V
LV Input Voltage . . . . . . . . . . (OUT – 0.3 V) to (V+, +0.3 V)
FC and OSC Input Voltage
. . . . . . . . . . . (OUT – 0.3 V) or (V+, –6 V) to (V+, +0.3 V)
OUT, V+ Output Current (Continuous) . . . . . . . . . . . 120 mA
Output Short Circuit Duration to GND . . . . . . . . . . . 10 secs
Power Dissipation, N-8 . . . . . . . . . . . . . . . . . . . . . . . 625 mW
(Derate 8.3 mW/°C above +50°C)
θ
JA
, Thermal Impedance . . . . . . . . . . . . . . . . . . . . 120°C/W
Power Dissipation, R-8 . . . . . . . . . . . . . . . . . . . . . . . 450 mW
(Derate 6 mW/°C above +50°C)
θ
JA
, Thermal Impedance . . . . . . . . . . . . . . . . . . . . 170°C/W
ORDERING GUIDE
Temperature Package
Model Range Options
*
ADM660AN –40°C to +85°CN-8
ADM660AR –40°C to +85°CR-8
ADM660ARU –40°C to +85°CRU-16
ADM8660AN –40°C to +85°CN-8
ADM8660AR –40°C to +85°CR-8
*
N = Plastic DIP; RU = Thin Shrink Small Outline; RN = Small Outline.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although the
ADM660/ADM8660 features proprietary ESD protection circuitry, permanent damage may occur on
devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are
recommended to avoid performance degradation or loss of functionality.
REV. B–4–
ADM660/ADM8660
Doubler Configuration (ADM660 Only)
Mnemonic Function
FC Frequency Control Input for Internal Oscillator
and Charge Pump. With FC = Open, f
CP
=
25 kHz; with FC = V+, f
CP
= 120 kHz.
CAP+ Positive Charge-Pump Capacitor Terminal.
GND Positive Input Supply.
CAP– Negative Charge-Pump Capacitor Terminal.
OUT Ground.
LV Low Voltage Operation Input. Connect to OUT.
OSC Must be left unconnected in this mode.
V+ Doubled Positive Output.
PIN CONNECTIONS
8-Lead
1
2
3
4
8
7
6
5
TOP VIEW
(Not to Scale)
ADM660
FC
OUT
LV
OSC
V+
CAP+
GND
CAP–
1
2
3
4
8
7
6
5
TOP VIEW
(Not to Scale)
ADM8660
FC
OUT
LV
SD
V+
CAP+
GND
CAP–
16-Lead
14
13
12
11
16
15
10
9
8
1
2
3
4
7
6
5
TOP VIEW
(Not to Scale)
ADM660
NC = NO CONNECT
NC
OSC
V+
NC
NC
NC
FC
CAP+
NC
OUT
LVGND
CAP–
NC
NC NC
Inverter Configuration
Mnemonic Function
FC Frequency Control Input for Internal Oscillator
and Charge Pump. With FC = Open (ADM660)
or connected to GND (ADM8660), f
CP
= 25 kHz;
with FC = V+, f
CP
= 120 kHz.
CAP+ Positive Charge-Pump Capacitor Terminal.
GND Power Supply Ground.
CAP– Negative Charge-Pump Capacitor Terminal.
OUT Output, Negative Voltage.
LV Low Voltage Operation Input. Connect to GND
when input voltage is less than 3.5 V. Above
3.5 V, LV may be connected to GND or left
unconnected.
OSC ADM660: Oscillator Control Input. OSC is
connected to an internal 15 pF capacitor. An
external capacitor may be connected to slow the
oscillator. An external oscillator may also be
used to overdrive OSC. The charge-pump
frequency is equal to 1/2 the oscillator frequency.
SD ADM8660: Shutdown Control Input. This in-
put, when high, is used to disable the charge
pump thereby reducing the power consumption.
V+ Positive Power Supply Input.
PIN FUNCTION DESCRIPTIONS
REV. B
Typical Performance Characteristics–ADM660/ADM8660
–5–
SUPPLY VOLTAGE – Volts
0
1.5 7 .5
SUPPLY CURRENT – mA
3.5 5.5
2.5
1.5
3.0
2.0
1.0
0.5
VOLTAGE DOUBLER
LV = OUT
LV = GND
LV = OPEN
TPC 1. Power Supply Current vs. Voltage
LOAD CURRENT – mA
–4.2
–3.0
–5.0
–3.8
–4.6
–3.4
0100
OUTPUT VOLTAGE – Volts
20 40 60 80
100
40
0
60
20
80
EFFICIENCY – %
EFFICIENCY
VOUT
TPC 2. Output Voltage and Efficiency vs. Load Current
LOAD CURRENT – mA
1.6
0
0.8
0.4
1.2
0 10020
OUTPUT VOLTAGE DROP
FROM SUPPLY VOLTAGE – Volts
40 60 80
V+ = +2.5V
V+ = +1.5V
V+ = +3.5V
V+ = +5.5V
V+ = +4.5V
TPC 3. Output Voltage Drop vs. Load Current
CHARGE-PUMP FREQUENCY – Hz
100
90
301k 1M10k 100k
70
60
50
40
80
POWER EFFICIENCY – %
I
L
= 10mA
I
L
= 1mA
I
L
= 50mA
I
L
= 80mA
TPC 4. Efficiency vs. Charge-Pump Frequency
CHARGE-PUMP FREQUENCY – kHz
3.5
3.0
01100010
SUPPLY CURRENT – mA
100
1.5
2.0
1.0
0.5
2.5
LV = GND
VOLTAGE DOUBLER
LV = GND
VOLTAGE INVERTER
TPC 5. Power Supply Current vs. Charge-Pump
Frequency
LOAD CURRENT – mA
120
EFFICIENCY – %
100
00 10020 40 60 80
80
60
40
20
V+ = +5.5V V+ = +4.5V
V+ = +6.5V
V+ = +1.5V V+ = +2.5V
V+ = +3.5V
TPC 6. Power Efficiency vs. Load Current
REV. B–6–
ADM660/ADM8660
CHARGE-PUMP FREQUENCY – kHz
4.5
01100010 100
1.5
0.5
2.5
5.0
2.0
1.0
3.0
4.0
3.5
LOAD = 1mA
OUTPUT VOLTAGE – Volts
LOAD = 10mA
LOAD = 50mA
LOAD = 80mA
TPC 7. Output Voltage vs. Charge-Pump Frequency
SUPPLY VOLTAGE – Volts
30
OUTPUT SOURCE RESISTANCE – ⍀
25
0
1.5 6.52.5 3.5 4.5 5.5
20
15
10
5
TPC 8. Output Source Resistance vs. Supply Voltage
SUPPLY VOLTAGE – Volts
30
01.5 3.5 5.5
20
10
2.5 4.5 6.5
LV = GND
LV = OPEN
FC = OPEN
OSC = OPEN
C1, C2 = 10F
CHARGE-PUMP FREQUENCY – kHz
TPC 9. Charge-Pump Frequency vs. Supply Voltage
TEMPERATURE – C
35
15
0
–40
CHARGE-PUMP FREQUENCY – kHz
–20 0 20 4060 80
30
25
10
5
20
LV = GND
FC = OPEN
C1, C2 = 10F
TPC 10. Charge-Pump Frequency vs. Temperature
CAPACITANCE –
p
F
CHARGE-PUMP FREQUENCY – kHz
1k
100
0.111k10 100
10
1
FC = OPEN
LV = GND
FC = V+
LV = GND
TPC 11. Charge-Pump Frequency vs. External
Capacitance
SUPPLY VOLTAGE – Volts
CHARGE-PUMP FREQUENCY – kHz
140
0
373.5 4 4.5 5 5.5 6 6.5
120
80
60
40
20
100
LV = GND
LV = OPEN
FC = V+
OSC = OPEN
C1,C2 = 2.2F
TPC 12. Charge-Pump Frequency vs. Supply Voltage
REV. B
ADM660/ADM8660
–7–
TEMPERATURE – C
CHARGE-PUMP FREQUENCY – kHz
–40 100–20 0 20 406080
160
0
140
80
60
40
20
120
100
LV = GND
FC = V+
C1, C2 = 2.2F
TPC 13. Charge-Pump Frequency vs. Temperature
TEMPERATURE – C
OUTPUT SOURCE RESISTANCE – ⍀
60
0
–40 100–20 0 20 406080
50
40
30
20
10
V+ = +1.5V
V+ = +3V
V+ = +5V
TPC 14. Output Resistance vs. Temperature
GENERAL INFORMATION
The ADM660/ADM8660 is a switched capacitor voltage con-
verter that can be used to invert the input supply voltage. The
ADM660 can also be used in a voltage doubling mode. The
voltage conversion task is achieved using a switched capacitor
technique using two external charge storage capacitors. An on-
board oscillator and switching network transfers charge between
the charge storage capacitors. The basic principle behind the
voltage conversion scheme is illustrated in Figures 1 and 2.
+
+
V+
S1
S2
S3
S4
CAP+
CAP–
C1
C2
OUT = –V+
Φ1Φ2
+ 2
OSCILLATOR
Figure 1. Voltage Inversion Principle
++
V+
S1
S2
S3
S4
CAP+
CAP–
C1 C2
VOUT = 2V+
Φ1Φ2
+ 2
OSCILLATOR
V+
Figure 2. Voltage Doubling Principle
Figure 1 shows the voltage inverting configuration, while Figure 2
shows the configuration for voltage doubling. An oscillator
generating antiphase signals φ1 and φ2 controls switches S1, S2,
and S3, S4. During φ1, switches S1 and S2 are closed charging
C1 up to the voltage at V+. During φ2, S1 and S2 open and S3
and S4 close. With the voltage inverter configuration during φ2,
the positive terminal of C1 is connected to GND via S3 and the
negative terminal of C1 connects to V
OUT
via S4. The net result
is voltage inversion at V
OUT
wrt GND. Charge on C1 is trans-
ferred to C2 during φ2. Capacitor C2 maintains this voltage
during φ1. The charge transfer efficiency depends on the on-
resistance of the switches, the frequency at which they are being
switched, and also on the equivalent series resistance (ESR) of
the external capacitors. The reason for this is explained in the
following section. For maximum efficiency, capacitors with low
ESR are, therefore, recommended.
The voltage doubling configuration reverses some of the con-
nections, but the same principle applies.
Switched Capacitor Theory of Operation
As already described, the charge pump on the ADM660/ADM8660
uses a switched capacitor technique in order to invert or double
the input supply voltage. Basic switched capacitor theory is
discussed below.
A switched capacitor building block is illustrated in Figure 3.
With the switch in position A, capacitor C1 will charge to voltage
V1. The total charge stored on C1 is q1 = C1V1. The switch is
then flipped to position B discharging C1 to voltage V2. The
charge remaining on C1 is q2 = C1V2. The charge transferred
to the output V2 is, therefore, the difference between q1 and
q2, so ∆q = q1–q2 = C1 (V1–V2).
V1 AB
C1
C2 R
L
V2
Figure 3. Switched Capacitor Building Block
As the switch is toggled between A and B at a frequency f, the
charge transfer per unit time or current is:
I=f(∆q)=f(C1)(V1–V2)
Therefore,
I=(V1–V2)/(1 / fC1) =(V1–V2)/(REQ )
where R
EQ
= 1/fC1
The switched capacitor may, therefore, be replaced by an equivalent
resistance whose value is dependent on both the capacitor size
and the switching frequency. This explains why lower capacitor
values may be used with higher switching frequencies. It should
be remembered that as the switching frequency is increased the
power consumption will increase due to some charge being lost
at each switching cycle. As a result, at high frequencies, the power
efficiency starts decreasing. Other losses include the resistance
of the internal switches and the equivalent series resistance (ESR)
of the charge storage capacitors.
V1
R
EQ
R
EQ
= 1/fC1
V2
C2 R
L
Figure 4. Switched Capacitor Equivalent Circuit
REV. B–8–
ADM660/ADM8660
Table II. ADM8660 Charge-Pump Frequency Selection
FC OSC Charge Pump C1, C2
GND Open 25 kHz 10 µF
V+ Open 120 kHz 2.2 µF
GND or V+ Ext Cap See Typical Characteristics
GND Ext CLK Ext CLK Frequency/2
+
+
+1.5V TO +7V
INPUT
C1
C2
INVERTED
NEGATIVE
OUTPUT
ADM660
ADM8660
FC
CAP+
GND
CAP–
V+
OSC
LV
OUT
CLK OSC
CMOS GATE
Figure 7. ADM660/ADM8660 External Oscillator
Voltage Doubling Configuration
Figure 8 shows the ADM660 configured to generate increased
output voltages. As in the inverting mode, only two external
capacitors are required. The doubling function is achieved by
reversing some connections to the device. The input voltage is
applied to the GND pin and V+ is used as the output. Input
voltages from 2.5 V to 7 V are allowable. In this configuration,
pins LV, OUT must be connected to GND.
The unloaded output voltage in this configuration is 2 (V
IN
).
Output resistance and ripple are similar to the voltage inverting
configuration.
Note that the ADM8660 cannot be used in the voltage
doubling configuration.
+
10F
DOUBLED
POSITIVE
OUTPUT
ADM660
FC
CAP+
GND
CAP–
V+
OSC
LV
OUT
+
10F
+2.5V
TO +7V
INPUT
Figure 8. Voltage Doubler Configuration
Shutdown Input
The ADM8660 contains a shutdown input that can be used to
disable the device and thus reduce the power consumption. A
logic high level on the SD input shuts the device down reducing
the quiescent current to 0.3 µA. During shutdown, the output
voltage goes to 0 V. Therefore, ground referenced loads are not
powered during this state. When exiting shutdown, it takes
several cycles (approximately 500 µs) for the charge pump to
reach its final value. If the shutdown function is not being used,
then SD should be hardwired to GND.
Capacitor Selection
The optimum capacitor value selection depends the charge-pump
frequency. With 25 kHz selected, 10 µF capacitors are recommended,
while with 120 kHz selected, 2.2 µF capacitors may be used.
Other frequencies allow other capacitor values to be used. For
maximum efficiency in all cases, it is recommended that capaci-
tors with low ESR are used for the charge-pump. Low ESR
capacitors give both the lowest output resistance and
lowest
ripple voltage. High output resistance degrades the overall
power
efficiency and causes voltage drops, especially at high output
Inverting Negative Voltage Generator
Figures 5 and 6 show the ADM660/ADM8660 configured to
generate a negative output voltage. Input supply voltages from
1.5 V up to 7 V are allowable. For supply voltage less than 3 V,
LV must be connected to GND. This bypasses the internal
regulator circuitry and gives best performance in low voltage
applications. With supply voltages greater than 3 V, LV may
be either connected to GND or left open. Leaving it open facili-
tates direct substitution for the ICL7660.
+
+
+1.5V TO +7V
INPUT
C1
10F
C2
10F
INVERTED
NEGATIVE
OUTPUT
ADM660
FC
CAP+
GND
CAP–
V+
OSC
LV
OUT
Figure 5. ADM660 Voltage Inverter Configuration
+
+
+1.5V TO +7V
INPUT
C1
10F
C2
10F
INVERTED
NEGATIVE
OUTPUT
ADM8660
FC
CAP+
GND
CAP–
V+
LV
OUT
SD
SHUTDOWN
CONTROL
Figure 6. ADM8660 Voltage Inverter Configuration
OSCILLATOR FREQUENCY
The internal charge-pump frequency may be selected to be
either 25 kHz or 120 kHz using the Frequency Control (FC)
input. With FC unconnected (ADM660) or connected to GND
(ADM8660), the internal charge pump runs at 25 kHz while, if
FC is connected to V+, the frequency is increased by a factor of
five. Increasing the frequency allows smaller capacitors to be
used for equivalent performance or, if the capacitor size is un-
changed, it results in lower output impedance and ripple.
If a charge-pump frequency other than the two fixed values is
desired, this is made possible by the OSC input, which can
either have a capacitor connected to it or be overdriven by an
external clock. Refer to the Typical Performance Characteris-
tics, which shows the variation in charge-pump frequency versus
capacitor size. The charge-pump frequency is one-half the oscil-
lator frequency applied to the OSC pin.
If an external clock is used to overdrive the oscillator, its levels
should swing to within 100 mV of V+ and GND. A CMOS
driver is, therefore, suitable. When OSC is overdriven, FC has
no effect but LV must be grounded.
Note that overdriving is permitted only in the voltage inverter
configuration.
Table I. ADM660 Charge-Pump Frequency Selection
FC OSC Charge Pump C1, C2
Open Open 25 kHz 10 µF
V+ Open 120 kHz 2.2 µF
Open or V+ Ext Cap See Typical Characteristics
Open Ext CLK Ext CLK Frequency/2
REV. B
ADM660/ADM8660
–9–
current levels. The ADM660/ADM8660 is tested using low
ESR, 10 µF, capacitors for both C1 and C2. Smaller values of
C1 increase the output resistance, while increasing C1 will
reduce the output resistance. The output resistance is also depen-
dent on the internal switches on resistance as well as the
capacitors ESR, so the effect of increasing C1 becomes negligible
past a certain point.
Figure 9 shows how the output resistance varies with oscillator
frequency for three different capacitor values. At low oscillator
frequencies, the output impedance is dominated by the 1/f
C
term. This explains why the output impedance is higher for
smaller capacitance values. At high oscillator frequencies, the
1/f
C
term becomes insignificant and the output impedance is
dominated by the internal switches on resistance. From an out-
put impedance viewpoint, therefore, there is no benefit to be
gained from using excessively large capacitors.
OSCILLATOR FREQUENCY – kHz
500
400
0
0.1 100110
300
200
100
C1 = C2 = 2.2F
C1 = C2 = 1F
C1 = C2 = 10F
OUTPUT RESISTANCE – ⍀
Figure 9. Output Impedance vs. Oscillator Frequency
Capacitor C2
The output capacitor size C2 affects the output ripple. Increas-
ing the capacitor size reduces the peak-to-peak ripple. The ESR
affects both the output impedance and the output ripple.
Reducing the ESR reduces the output impedance and ripple.
For convenience it is recommended that both C1 and C2 be the
same value.
Table III. Capacitor Selection
Charge-Pump Capacitor
Frequency C1, C2
25 kHz 10 µF
120 kHz 2.2 µF
Power Efficiency and Oscillator Frequency Trade-Off
While higher switching frequencies allow smaller capacitors to
be used for equivalent performance, or improved performance
with the same capacitors, there is a trade-off to consider. As the
oscillator frequency is increased, the quiescent current increases.
This happens as a result of a finite charge being lost at each
switching cycle. The charge loss per unit cycle at very high
frequencies can be significant, thereby reducing the power effi-
ciency. Since the power efficiency is also degraded at low oscillator
frequencies due to an increase in output impedance, this means
that there is an optimum frequency band for maximum power
transfer. Refer to the Typical Performance Characteristics section.
Bypass Capacitor
The ac impedance of the ADM660/ADM8660 may be reduced
by using a bypass capacitor on the input supply. This capacitor
should be connected between the input supply and GND. It
will provide instantaneous current surges as required. Suitable
capacitors of 0.1 µF or greater may be used.
REV. B–10–
ADM660/ADM8660
8-Lead Plastic Dual-in-Line Package [PDIP]
(N-8)
Dimensions shown in inches and (millimeters)
SEATING
PLANE
0.015
(0.38)
MIN
0.180
(4.57)
MAX
0.150 (3.81)
0.130 (3.30)
0.110 (2.79) 0.060 (1.52)
0.050 (1.27)
0.045 (1.14)
8
14
50.295 (7.49)
0.285 (7.24)
0.275 (6.98)
0.100 (2.54)
BSC
0.375 (9.53)
0.365 (9.27)
0.355 (9.02)
0.150 (3.81)
0.135 (3.43)
0.120 (3.05)
0.015 (0.38)
0.010 (0.25)
0.008 (0.20)
0.325 (8.26)
0.310 (7.87)
0.300 (7.62)
0.022 (0.56)
0.018 (0.46)
0.014 (0.36)
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
COMPLIANT TO JEDEC STANDARDS MO-095AA
8-Lead Standard Small Outline Package [SOIC]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
0.25 (0.0098)
0.19 (0.0075)
1.27 (0.0500)
0.41 (0.0160)
0.50 (0.0196)
0.25 (0.0099) ⴛ 45ⴗ
8ⴗ
0ⴗ
1.75 (0.0688)
1.35 (0.0532)
SEATING
PLANE
0.25 (0.0098)
0.10 (0.0040)
85
41
5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
1.27 (0.0500)
BSC
6.20 (0.2440)
5.80 (0.2284)
0.51 (0.0201)
0.33 (0.0130)
COPLANARITY
0.10
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
COMPLIANT TO JEDEC STANDARDS MS-012AA
OUTLINE DIMENSIONS
16-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-16)
Dimensions shown in millimeters
16 9
81
PIN 1
SEATING
PLANE
8ⴗ
0ⴗ
4.50
4.40
4.30
6.40
BSC
5.10
5.00
4.90
0.65
BSC
0.15
0.05
1.20
MAX
0.20
0.09 0.75
0.60
0.45
0.30
0.19
COPLANARITY
0.10
COMPLIANT TO JEDEC STANDARDS MO-153AB
REV. B
ADM660/ADM8660
–11–
Revision History
Location Page
12/02—Data Sheet changed from REV. A to REV. B.
Renumbered TPCs and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . UNIVERSAL
Edits to SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Updated ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
C00082–0–12/02(B)
PRINTED IN U.S.A.
–12–
