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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 IN 2 6 CAP+ 5 SHDN TOP VIEW (Not to Scale) 4 CAP- 3 GND
ADM8828
OUT 1 IN 2
6 CAP+
5 NC TOP VIEW (Not to Scale) 4 CAP- 3 GND NC = NO CONNECT
ADM8829
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 quiescent current to 20 nA. The ADM8828/ADM8829 is available in a 6-lead SOT-23 package.
+1.5V TO +5.5V INPUT CAP+ C1 + 1F
IN
ADM8828/ ADM8829
CAP- SHDN SHUTDOWN CONTROL INVERTED NEGATIVE OUTPUT
GND
OUT C2 +1 F
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 (c) Analog Devices, Inc., 1999
ADM8828/ADM8829-SPECIFICATIONS
Parameter Input Voltage, IN Supply Current Output Current Output Resistance Output Ripple Charge-Pump Frequency Power Efficiency Voltage Conversion Efficiency 99.5 25 18 25 130 50 65 120 90 87 99.96 98 91 0.02 2.0 0.8 Shutdown Exit Time 175
NOTES 1 C1 and C2 are low ESR (<0.2 ) electrolytic capacitors. High ESR will degrade performance. Specifications subject to change without notice.
(VIN = +5 V, C1, C2 = 1 F,1 TA = TMIN to TMAX unless otherwise noted)
Units V A mA mV p-p mV p-p kHz kHz % % % % % Test Conditions/Comments RL = 10 k Unloaded IL = 5 mA IL = 5 mA IL = 25 mA VIN = +2.25 V RL = 200 RL = 1 k No Load RL = 1 k RL = 200 SHDN = IN SHDN High = Disabled SHDN Low = Enabled IL = 5 mA
Min 1.5
Typ
Max 5.5
600
1000 28
190
Shutdown Supply Current, ISHDN Shutdown Input Voltage, VSHDN
2
A V V s
ABSOLUTE MAXIMUM RATINGS*
(TA = +25C unless otherwise noted)
PIN FUNCTION DESCRIPTIONS
Input Voltage (IN to GND) . . . . . . . . . . . . . . . -0.3 V to +6 V OUT to GND . . . . . . . . . . . . . . . . . . . . . . . . -6.0 V to +0.3 V OUT, IN Output Current (Continuous) . . . . . . . . . . . . 50 mA Output Short Circuit Duration to GND . . . . . . . . . . . 10 secs Power Dissipation, RT-6 . . . . . . . . . . . . . . . . . . . . . . 570 mW (Derate 8.3 mW/C above +70C) JA, Thermal Impedance . . . . . . . . . . . . . . . . . . . . 120C/W Operating Temperature Range Industrial (A Version) . . . . . . . . . . . . . . . . - 40C to +85C Storage Temperature Range . . . . . . . . . . . -65C to +150C Lead Temperature Range (Soldering 10 sec) . . . . . . . . +300C Vapor Phase (70 sec) . . . . . . . . . . . . . . . . . . . . . . . . +215C Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . +220C ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >3500 V
*This is a stress rating only and 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.
Mnemonic CAP+ GND CAP- OUT SHDN
Function Positive Charge-Pump Capacitor Terminal. Power Supply Ground. Negative Charge-Pump Capacitor Terminal. Output, Negative Voltage. Shutdown Control Input. This input, when high, is used to disable the charge pump thereby reducing the power consumption. Positive Power Supply Input.
IN
PIN CONFIGURATIONS
OUT 1
6 CAP+
5 SHDN IN 2 TOP VIEW (Not to Scale) 4 CAP- 3 GND
ADM8828
ORDERING GUIDE
Model ADM8828ART ADM8829ART
Temperature Range -40C to +85C -40C to +85C
Branding Information MM0 MN0
Package Option* RT-6 RT-6
OUT 1 IN 2
6 CAP+
5 NC TOP VIEW (Not to Scale) 4 CAP- 3 GND NC = NO CONNECT
ADM8829
*RT-6 = 6-lead SOT-23.
-2-
REV. A
Typical Performance Characteristics- ADM8828/ADM8829
0.8
60 IL = 5mA
OUTPUT VOLTAGE RIPPLE - mV p-p
0.7
50
SUPPLY CURRENT - mA
0.6 0.5 0.4 0.3 0.2 0.1 0 1 1.5 2 2.5 3 3.5 4 SUPPLY VOLTAGE - V 4.5 5 5.5
OUTPUT VOLTAGE RIPPLE @ VIN = 4.75V
40
30
OUTPUT VOLTAGE RIPPLE @ VIN = 1.9V
20 OUTPUT VOLTAGE RIPPLE @ VIN = 3.15V
10
0 0.47
1 2.2 CAPACITANCE - F
3.3
Figure 2. Power Supply Current vs. Voltage
Figure 5. Output Voltage Ripple vs. Capacitance
35 30
350
OUTPUT VOLTAGE RIPPLE - mV p-p
300
OUTPUT VOLTAGE RIPPLE @ VIN = 4.75V, VOUT = -4.0V
OUTPUT RESISTANCE -
25 20 15
250 200 150 OUTPUT VOLTAGE RIPPLE @ VIN = 3.15V, VOUT = -2.5V
10 5 0 1.5
100 50
2
2.5
3 3.5 4 SUPPLY VOLTAGE - V
4.5
5
5.5
OUTPUT VOLTAGE RIPPLE @ VIN = 1.9V, VOUT = -1.5V 0 2.2 0.47 1 CAPACITANCE - F
3.3
Figure 3. Output Source Resistance vs. Supply Voltage
Figure 6. Output Voltage Ripple vs. Capacitance
20 18 16 OUTPUT CURRENT @ VIN = 4.75V
0 -0.5 -1
OUTPUT VOLTAGE @ VIN = 2.0V
OUTPUT CURRENT - mA
14 12 10 8 6 4 2 0 0.47 2.2 1 CAPACITANCE - F 3.3 OUTPUT CURRENT @ VIN = 1.9V OUTPUT CURRENT @ VIN = 3.15V
OUTPUT VOLTAGE - V
-1.5 -2 OUTPUT VOLTAGE @ VIN = 3.3V -2.5 -3 -3.5 -4 -4.5 -5 0 5 10 15 20 25 30 OUTPUT CURRENT - mA 35 40 45 OUTPUT VOLTAGE @ VIN = 5.0V
Figure 4. Output Current vs. Capacitance
Figure 7. Output Voltage vs. Output Current
REV. A
-3-
ADM8828/ADM8829
100 PEFF @ VIN = 5.0V 90 80 70
200 180 160
PUMP FREQUENCY - kHz
PEFF @ VIN = 3.3V PEFF @ VIN = 2.0V
PUMP FREQUENCY @ VIN = 3.3V PUMP FREQUENCY @ VIN = 5.0V
140 120 100 80 60 40 20 PUMP FREQUENCY @ VIN = 1.5V
PEFF - %
60 50 40 30 20 10 0 0 5 10 15 20 25 30 IOUT - mA 35 40 45 50
0 -50
-30
-10
10
25 40 60 80 TEMPERATURE - C
90
110
125
Figure 8. Power Efficiency vs. Output Current
Figure 10. Charge Pump Frequency vs. Temperature
50 45 40
OUTPUT RESISTANCE -
RESISTANCE ( ) @ VIN = 1.5V
35 30 25 20 15 10 5 0 -50 -30 -10 10 25 40 60 80 TEMPERATURE - C 90 110 125 RESISTANCE ( ) @ VIN = 5.0V RESISTANCE ( ) @ VIN = 3.3V
Figure 9. Output Resistance vs. Temperature
-4-
REV. A
ADM8828/ADM8829
GENERAL INFORMATION Capacitor Selection
The ADM8828/ADM8829 is a switched capacitor voltage converter that can be used to invert the input supply voltage. The voltage conversion task is achieved using a switched capacitor 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 + 2 C2
The flying capacitor C1 can be increased to reduce the output resistance. The output capacitor size C2 affects the output ripple. Increasing 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 capacitors of 1 F or greater may be used.
+1.5V TO +5.5V INPUT CAP+ C1 + 1F
CAP- 1 2 OSCILLATOR
OUT = -V+
Figure 11. Voltage Inversion Principle
An oscillator generating antiphase signals 1 and 2 controls switches S1, S2 and S3, S4. During 1, switches S1 and S2 are closed while S3 and S4 are open, thereby charging C1 up to the voltage at V+. During 2, 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 2. Capacitor C2 maintains this voltage during 1. 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 efficiency, capacitors with low ESR are, therefore, recommended.
Shutdown Input
IN
ADM8828/ ADM8829
CAP- SHDN SHUTDOWN CONTROL INVERTED NEGATIVE OUTPUT
GND
OUT C2 +1 F
Figure 12. Typical Circuit Configuration
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 A. During shutdown the output voltage discharges to 0 V. Therefore, ground referenced loads are not powered during this state. When exiting shutdown, it takes several cycles (approximately 175 s) for the charge pump to reach its final value. If the shutdown function is not being used, SHDN should be hardwired to GND.
REV. A
-5-
ADM8828/ADM8829
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
6-Lead SOT-23 (RT-6)
0.122 (3.10) 0.106 (2.70)
0.071 (1.80) 0.059 (1.50) PIN 1
6 1
5 2
4 3
0.118 (3.00) 0.098 (2.50)
0.037 (0.95) BSC 0.075 (1.90) BSC 0.051 (1.30) 0.035 (0.90) 0.006 (0.15) 0.000 (0.00) 0.057 (1.45) 0.035 (0.90) 0.020 (0.50) SEATING 0.010 (0.25) PLANE 10 0.009 (0.23) 0 0.003 (0.08) 0.022 (0.55) 0.014 (0.35)
-6-
REV. A
PRINTED IN U.S.A.
C3352a-0-10/99

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