Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Utility Patent
1999-07-15
2001-01-02
Kim, Jung Ho (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S540000, C363S060000
Utility Patent
active
06169444
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to electronic circuits for conversion of direct current power, and more particularly to systems for regulating high-efficiency charge pump circuits.
BACKGROUND ART
Electronic circuits today often require power in one or more specific direct current (DC) voltage ranges. Supplying such, however, can pose a number of problems. If only one supply voltage is needed, it may not be of a value easily obtainable from available sources, like standard battery cells. Source-requirements mating can therefore be one problem encountered, and source voltage conversion may thus be desirable or necessary. A source also may not supply voltage which is consistently in a desired range. Batteries again provide a good example. Battery voltage varies with load, charge, temperature, etc. Such source voltage variation therefore can also be a problem, and source voltage regulation may thus also be desirable or necessary. Of course, when multiple supply voltages are needed, such power source problems increase accordingly.
For many electronic circuits it is particularly desirable to use only one power source, and to increase, decrease, or invert the voltage from it, and to also regulate the power from it for all needs. This is the case for portable electronic devices, such as cellular telephones, personal digital assistants, global position sensors etc. But even for non portable devices this is often desirable, since it permits construction of circuits which are smaller, more reliable, cheaper, etc.
Various power conversion and regulation systems currently exist. Of present interest is the charge pump. It is one of the most widely used such systems today. A charge pump is a capacitor and oscillator based circuit which converts a DC input to a DC output which is either higher, lower, or alternately both, or inverted in voltage value. Charge pumps can be regulated using a number of schemes, and they can include options, such as extreme condition detection and circuit shut-down capability, which adds to their versatility and commercial acceptance.
On initial consideration, the charge pump seems to be a perfect solution to many power conversion needs. But unfortunately that is not the case. Contrary to a somewhat popular belief, charge pumps are not particularly efficient at power conversion, and they are especially not so when used for supplying varying loads. This can severely limit their use with battery and other limited power sources where power must be used efficiently. Further, even when power availability is not a concern, the use of charge pumps can be limited because inefficiency is ultimately manifested as heat which must be dissipated. Still further, since charge pumps are inherently oscillator based systems, unacceptable “artifacts” such as output voltage ripple and electromagnetic radiation can be present from the conversion process they use. Charge pumps can be implemented using integrated circuits (ICs), but the number, size, and types of external components used may then be areas of concern. This is particularly the case for capacitors used with charge pumps, where any capacitance value and physical size reduction is usually highly desirable.
This discussion now turns to some specific charge pump examples. To avoid confusion, the following will generally be limited to coverage of charge pumps which increase voltage, i.e. step-up charge pumps. However, as skilled practitioners of the electronic arts should readily appreciate, these principles are easily extended to other types of charge pumps as well, such as voltage inverting and step-down types.
FIG. 1
(prior art) is a block diagram of a charge pump circuit employing an IC (specifically, the current version of part MAX682 by Maxim Integrated Products of Sunnyvale, Calif.). Input power is supplied across an input capacitor (C-IN) to appropriate terminals of the IC device. A flying capacitor (C-X) (often also called a transfer capacitor) is connected to other IC terminals (CXP and CXN) to operate in concert with the IC's internal components, discussed presently. Output power is then produced by the IC across an output capacitor (C-OUT). Other components may be present for optional features.
FIG. 2
(prior art) is a functional block diagram of the IC of FIG.
1
. Of particular interest are an oscillator (OSC), switches which control power flow to the terminals (CXP and CXN) for the external flying capacitor, and control logic and sensing and tailoring elements used for signals to that control logic.
FIG. 3
(prior art) is a block diagram of an unregulated voltage doubler, i.e. a very simple charge pump. The oscillator (OSC) is free running and the charge and discharge paths to the flying capacitor (C-X) are merely switched (via S
1
and S
2
). Actually,
FIG. 3
depicts a simplistic switching scheme, and
FIG. 4
depicts a more common case using four switches S
1
, S
2
, S
3
, and S
4
). The input capacitor (C-IN) and the output capacitor (C-OUT) respectfully act as input and output reservoirs, smoothing out fluctuations as conversion proceeds (e.g., ripple). Unless the output is overloaded, the output voltage (V-OUT) from the circuit in
FIG. 3
is almost double the input voltage (V-IN). A voltage doubler is too inflexible for use in most applications, and most charge pumps today employ one of two common regulation schemes to permit adjustment of the output voltage to either a value at initial circuit design or to one which a user can pick by using appropriate components later. Modem IC based systems, such as that in
FIG. 1
, can often be configured to use either of these common regulation schemes.
FIG. 5
(prior art) is a block diagram illustrating a skip mode charge pump regulation scheme being used to increase or “step-up” the voltage. Each cycle of the oscillator (OSC) results in the output voltage (V-OUT) being increased as the charge in the flying capacitor (C-X), which can be termed a “quanta,” is “stacked” onto the output capacitor (C-OUT). The flying capacitor (C-X) is chosen to have a lower capacitance than the output capacitor (C-OUT) so that the output voltage (V-OUT) is increased a small amount during each oscillator cycle. Regulation is accomplished in this scheme by enabling the oscillator with feedback from the output (V-OUT). A sample is taken from resistors (R
1
and R
2
) forming a voltage divider across the circuit's output. This sample from the feedback is compared to the voltage from a reference (REF) with a comparator (COMP). When the output voltage (V-OUT) is determined in this manner to be below a desired value the oscillator operates the switches (S
1
and S
2
) to charge the flying capacitor (C-X) from the input with a new quanta during a first half-cycle and to transfer that quanta to the output during the next half-cycle. When the output voltage (V-OUT) increases to the desired level the oscillator (OSC) is turned off, i.e., dis-enabled. As the output voltage drops, due to power use by the ultimate load (not shown), the oscillator is re-enabled and additional quanta are transferred.
Skip mode regulation is simple but it has some disadvantages. Voltage ripple in the output can be high, and this can be very difficult to filter out because of the varying frequency as the oscillator “skips.” The values needed for the external component can also be large, and for the capacitors this particularly means that they may be more sizable and expensive than desired. For this mode of regulation the ratio for values between the flying capacitor and the output capacitor is typically about 1:20. The MAX682 component provides an example. This widely used IC can step-up a 3.3 volt input to a regulated 5.0 volt output for loads up to 250 milli amps (mA). Configured for skip mode, the output voltage ripple rating is 100 milli volts (mV) and the recommended capacitor values are: 2.2 micro farads (uF) for the input capacitor (C-IN), 1 uF for the flying capacitor (C-X), and 10 uF for a ceramic type output capacitor. In view of the large output capacitance needed, a tanta
Hickman Coleman & Hughes LLP
Kim Jung Ho
Maxim Integrated Products Inc.
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