ADM8828ART-REEL Analog Devices Inc, ADM8828ART-REEL Datasheet - Page 5

• Manufacturer Part Number: ADM8828ART-REEL
• Description: IC,DC/DC CONVERTER,-1.5/-5.5V,CMOS,TSOP,6PIN
• Manufacturer: Analog Devices Inc
• Type: Step-Up (Boost), Switched Capacitor (Charge Pump), Invertingr

Specifications of ADM8828ART-REEL

• Rohs Status: RoHS non-compliant
• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: -1.5 ~ -5.5 V
• Current - Output: 25mA
• Voltage - Input: 1.5 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-6
• Power - Output: 570mW
• Frequency - Switching: -

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.
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 V
via S4. The net result is voltage inversion at V
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 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 A. 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 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
V+
Figure 11. Voltage Inversion Principle
S1
S2
1
OSCILLATOR
CAP+
CAP–
+
C1
2
S3
S4
2
+
C2
OUT = –V+
OUT
wrt GND.
OUT
–5–
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 F or greater may be used.
1 F
C1
Figure 12. Typical Circuit Configuration
+
CAP+
CAP–
GND
ADM8828/
ADM8829
ADM8828/ADM8829
SHDN
OUT
+1.5V TO +5.5V
IN
INPUT
+
C2
1 F
SHUTDOWN
CONTROL
INVERTED
NEGATIVE
OUTPUT