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PDF ADM8829 Data sheet ( Hoja de datos )
| Número de pieza | ADM8829 | |
| Descripción | Switched-Capacitor Voltage Inverter with Shutdown | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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FEATURES
Inverts Input Supply Voltage
99% Voltage Conversion Efficiency
25 mA Output Current
Shutdown Function
Requires Only Two Capacitors
1 F Capacitors
18 ⍀ Output Resistance
+1.5 V to +5.5 V Input Range
600 A Quiescent Current
20 nA Shutdown Current (ADM8828)
APPLICATIONS
Handheld Instruments
LCD Panels
Cellular Phones
PDAs
Remote Data Acquisition
Op Amp Power Supplies
Switched-Capacitor
Voltage Inverter with Shutdown
ADM8828/ADM8829
FUNCTIONAL BLOCK DIAGRAMS
OUT 1
6 CAP+
ADM8828
IN 2 TOP VIEW 5 SHDN
CAP– 3 (Not to Scale) 4 GND
OUT 1
6 CAP+
ADM8829
IN 2 TOP VIEW 5 NC
CAP– 3 (Not to Scale) 4 GND
NC = NO CONNECT
GENERAL DESCRIPTION
The ADM8828/ADM8829 is a charge-pump voltage inverter
which may be used to generate a negative supply from a positive
input. Input voltages ranging from +1.5 V to +5.5 V can be
inverted into a negative –1.5 V to –5.5 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 25 mA with
greater than 99% efficiency are achievable.
The ADM8828 also features a low power shutdown (SHDN)
pin. This can be used to disable the device and reduce the quies-
cent current to 20 nA.
The ADM8828/ADM8829 is available in a 6-lead SOT-23
package.
+1.5V TO +5.5V
INPUT
C1 +
1F
CAP+
IN
ADM8828/
ADM8829
CAP–
SHDN
GND
OUT
SHUTDOWN
CONTROL
C2
+ 1F
INVERTED
NEGATIVE
OUTPUT
Figure 1. Typical Circuit Configuration
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1999
1 page  
ADM8828/ADM8829
GENERAL INFORMATION
The ADM8828/ADM8829 is a switched capacitor voltage con-
verter that can be used to invert the input supply voltage.
The voltage conversion task is achieved using a switched capaci-
tor technique using two external charge storage capacitors. An
on-chip oscillator and switching network transfers charge between
the charge storage capacitors. The basic principle behind the
voltage conversion scheme is illustrated below.
V+ S1
S2
CAP+
+
C1
S3
S4
CAP–
⌽1 ، 2 ⌽2
OSCILLATOR
OUT = –V+
+
C2
Figure 11. Voltage Inversion Principle
An oscillator generating antiphase signals φ1 and φ2 controls
switches S1, S2 and S3, S4. During φ1, switches S1 and S2 are
closed while S3 and S4 are open, thereby charging C1 up to the
voltage at V+. During φ2, S1 and S2 open and S3 and S4 close.
The positive terminal of C1 is connected to GND via S3 during
this phase and the negative terminal of C1 connects to VOUT
via S4. The net result is voltage inversion at VOUT wrt GND.
Charge on C1 is transferred 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. For maximum effi-
ciency, capacitors with low ESR are, therefore, recommended.
Shutdown Input
The ADM8828 contains a shutdown input that can be used to
disable the device and hence reduce the power consumption. A
logic high level on the SHDN input shuts the device down
reducing the quiescent current to 0.02 µA. During shutdown
the output voltage discharges to 0 V. Therefore, ground ref-
erenced loads are not powered during this state. When exiting
shutdown, it takes several cycles (approximately 175 µs) for the
charge pump to reach its final value. If the shutdown function is
not being used, SHDN should be hardwired to GND.
Capacitor Selection
The flying capacitor C1 can be increased to reduce the output
resistance.
The output capacitor size C2 affects the output ripple. Increas-
ing the capacitor size reduces the peak-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.
The ac impedance of the ADM8828/ADM8829 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 capaci-
tors of 1 µF or greater may be used.
C1 +
1F
+1.5V TO +5.5V
INPUT
CAP+
IN
ADM8828/
ADM8829
CAP–
SHDN
GND
OUT
SHUTDOWN
CONTROL
C2
+ 1F
INVERTED
NEGATIVE
OUTPUT
Figure 12. Typical Circuit Configuration
REV. A
–5–
5 Page | ||
| Páginas | Total 6 Páginas | |
| PDF Descargar | [ Datasheet ADM8829.PDF ] | |
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