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GS7660IS Schematic ( PDF Datasheet ) - Vishay Siliconix

Teilenummer GS7660IS
Beschreibung Switched-Capacitor Voltage Converter
Hersteller Vishay Siliconix
Logo Vishay Siliconix Logo 




Gesamt 9 Seiten
GS7660IS Datasheet, Funktion
GS7660
New Product
Vishay
formerly General Semiconductor
Switched-Capacitor Voltage Converter
8 Pin Dip
SO-8
Features
Low output impedance ( typical 35at VIN = 5V )
Low quiescent current ( typical 36µA at VIN = 5V)
High power conversion efficiency ( typical 98% )
Simple and accurate voltage conversion from
positive to negative polarities
Improved latch-up protection
No external diodes required
Applications
• – 5V supply from + 5V logic supply
EIA/TIA 232E and EIA/TIA 562 power supplies
Portable telephones
Data acquisition systems
Personal communications equipment
Panel meters
Handheld instruments
Description
The GS7660 is a monolithic CMOS switched capacitor
voltage converter, designed to be an improved direct
replacement of the popular ICL7660, MAX1044 and
LTC1044. They perform supply voltage conversions from
positive to negative for an input voltage range of +1.5V to
+6.0V to their negative complements of –1.5V to –6.0V.
The input voltage can also be doubled (VOUT = 2VIN),
halved (VOUT = VIN/2), or multiplied (VOUT = ± n.VIN).
Contained on the chip are a series Power Supply regula-
tor, Oscillator, control Circuitry and four Power MOS
Switches. The oscillator, when unloaded, oscillates at a
nominal frequency of 10 kHz, with an Input voltage of 5.0V.
This frequency can be lowered by the addition of an external
capacitor to the “Osc” terminal or overdriven by an external
frequency source.
An Oscillator “boost” function is available to increase the
oscillator frequency which will optimize performance of
certain parameters. The Lv input can be connected to
ground to improve low voltage operation (VIN 3V), or left
open for input voltages greater than 3V to reduce power
dissipation.
The GS7660 provides superior performance over earlier
designs by combining low output impedance and low qui-
escent current with high efficiency and by eliminating diode
voltage drop losses. The only external components
required are two low cost electrolytic capacitors.
Typical Application Circuit
VIN (1.5V to 6V)
10µF +
C1
15
26
GS7660
37
Required for
VIN 3V
4 8 VOUT = --VIN
10µF
+ C2
Negative Voltage Converter
Document Number 74819
24-May-02
www.vishay.com
1






GS7660IS Datasheet, Funktion
GS7660
Vishay
formerly General Semiconductor
f
VIN
VOUT
C1 C2 RLOAD
Fig. 8 Switched Capacitor Model
To better understand the theory of operation, a review of
the basic switched capacitor building block is helpful (see
Fig. 8). Referring to Fig. 8 and looking at one full cycle of
operation, the charge being drained by the load is Qavg or
IL x T (T being the time period of one full cycle).
All the charge (q) flowing into the output is being delivered
by the input to C1 during only half the cycle. Under steady-
state condition, C1 will charge to the level of the input voltage
(VIN) and discharge to the peak level of the output voltage
(VOUT). Therefor the voltage change on C1 is VIN VOUT.
Qavg = q = C1(Vin Vout)
IL x T = C1(Vin Vout) or IL = f x C1(Vin Vout) f = 1/T
IL
=
(Vin
Vout)
1
and
REQUIV =
1
f x C1
(See fig. 9)
f x C1
Where f is one-half the oscillator frequency. This resistance
is a major component of the output resistance of switched
capacitor circuits.
With C1 = C2 = 10µF and Fosc = 10kHz, this resistance
represents 20.
Under the same conditions, the typical value in the
Electrical Characteristicssection of the GS7660 is 35.
Design Information
Low Voltage (LV) Pin
Fig. 10 (below) shows a simplified circuit diagram of the
GS7660.
It shows a voltage regulator between the VIN and Gnd, in
series with the Oscillator.
Grounding the LV pin removes the regulator from this
series path and improves low voltage performance down to
1.5V. For supply voltages less than 3.0V, the LV pin should
be connected to ground and left open for voltages above
3.0V.
The LV pin can be left grounded over the total range of
Input Voltages. This will improve low voltage operation and
increase oscillator frequency. The disadvantage is
increased quiescent current and reduced efficiency at
higher voltages.
1M
BOOST
pin 1
OSC
pin 7
Q
÷2 Q
LV
pin 6
VIN
pin 8
S1
CAP+
pin 2
S2
S3 S4
GND CAP-
pin 3 pin 4
VOUT
pin 5
Fig. 10 Functional Diagram
REQUIV
VIN
REQUIV =
1
f × C1
C2
VOUT
RLOAD
Fig. 9 Equivalent Impedance
www.vishay.com
6
Document Number 74819
24-May-02

6 Page







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