Hysteretic DC-DC converters

Details Hysteretic DC-DC converters Hysteretic DC-DC converters

2002-12-20

2004-10-05

Sterrett, Jeffrey (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C323S284000, C363S065000

Reexamination Certificate

active

06801026

ABSTRACT:

BACKGROUND
A power converter, such as a Direct Current (DC) to DC power converter for a microprocessor, may need to provide precise output voltage control (e.g., any output voltage ripple may need to be small), high efficiency, and fast transient response (e.g., the speed at which the converter responds when an output voltage rises too high or falls too low). Similarly, a maximum input current ripple and an overall size requirement may be imposed on the converter. Moreover, operating supply voltages for microprocessors and associated circuits have decreased, resulting in increased supply currents. The costs required to support these increased currents (e.g., via motherboards, sockets, and/or packages) have also increased.
One approach to providing an appropriate power converter is to use several smaller converter modules, each operating at the same frequency but at different phases. For example,
FIG. 1
is a diagram of a traditional Pulse Width Modulated (PWM) multi-phase DC-DC converter
100
that senses output voltage (V
OUT
) and output current. In particular, a voltage controller
110
compares V
OUT
with a reference voltage (V
REF
) to generate a voltage error signal. The voltage error signal is then used as a current reference by each converter module
120
(e.g., each of the four converter modules
120
illustrated in FIG.
1
).
A current controller
130
compares a module's output current with the reference current and generates a control signal that is used by a PWM modulator to determine a duty cycle to drive a bridge (e.g., via a driver
140
). Each PWM modulator includes a comparator
150
and a phase shifter
160
that receives a sawtooth waveform from an oscillator
170
(e.g., a waveform having a relatively large amplitude—such as several volts). In particular, the four phase shifters
160
illustrated in
FIG. 1
shift the waveform by 0, 90, 180 and 270 degrees. Note that the waveform from the oscillator
170
is injected after V
OUT
and V
REF
have been amplified.
Such a PWM converter
100
may provide small input current ripple and output voltage ripple. This approach, however, can suffer from slow transient response (e.g., orders of magnitude slower than what might be required for a microprocessor).
As another approach, a hysteretic converter (e.g., a “bang-bang” converter) may provide faster transient response. For example,
FIG. 2
is a diagram of a traditional hysteretic DC-DC converter
200
. Note that the converter's feedback loop includes a generic switching bridge
300
.
FIG. 3
illustrates some known switching bridges
310
,
320
. In particular, the first switching bridge
310
comprises a p-channel Metal-Oxide-Semiconductor (PMOS) device and a diode. The second switching bridge
320
comprises a PMOS device and an n-channel MOS (NMOS) device.
Referring again to
FIG. 2
, the hysteretic DC-DC converter
200
further includes a hysteretic comparator
210
that receives a reference voltage (V
REF
) via a first input. If an output voltage (V
OUT
) crosses one of the thresholds determined by the hysteresis window around V
REF
, the comparator
210
flips and rapidly pulls V
OUT
inside the window. For example, if V
OUT
drops below the window's lower threshold, the control circuit turns on the switching bridge
300
and connects the inductor
220
to the positive input power supply. Despite the advantage of a fast transient response, however, the switching frequency of the converter
200
is sensitive to circuit component parameters (e.g., there is no provision for externally setting the phase and frequency at which the converter
200
operates). As a result, the switching times of several identical converters
200
operating in parallel may be substantially the same—causing them to operate as a large single-phase converter (and producing a large output voltage ripple).
It is also known that voltage mode control may be used to reduce the sensitivity of a traditional hysteretic DC-DC converter
200
(e.g., by using an error amplifier to compare V
OUT
and V
REF
). This approach, however, may reduce the transient response time of the circuit. Similarly, it is know that V
2
mode control may be used to improve load current transient characteristics. In this case, however, the switching frequency and stability of the circuit may depend on output filter characteristics, such as the Equivalent Series Resistance (ESR) and the Equivalent Series Inductance (ESL) of an output capacitor, and any stray inductance and/or resistance associated with the supply path.


REFERENCES:
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patent: 6366069 (2002-04-01), Nguyen et al.
patent: 6489756 (2002-12-01), Kanouda et al.
patent: 6518738 (2003-02-01), Wang
patent: 6577109 (2003-06-01), Dancy et al.
patent: 6580258 (2003-06-01), Wilcox et al.
patent: 6605931 (2003-08-01), Brooks
patent: 6650556 (2003-11-01), Dinh et al.
patent: 6674274 (2004-01-01), Hobrecht et al.

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