Switch-mode power converter circuit

Details Switch-mode power converter circuit Switch-mode power converter circuit

1999-09-04

2001-01-09

Riley, Shawn (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

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

C323S224000, C363S060000

Reexamination Certificate

active

06172493

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
Cross reference is made to the following patent applications, each assigned to the same assignee, the teachings of which are incorporated herein by reference:
U.S. Pat. No.
Serial No.
Filing Date
Inventor
Title
TBD
09/389,691
09/04/99
Grant
Charge-Pump Closely
Coupled to Switching
Converter to Improve
Area Efficiency
TBD
09/389,810
09/04/99
Martinez, et al.
Controlled Linear Start-
up in Linear
Regulator
TBD
09/389,809
09/04/99
Grant et al.
Charge Pump Device
and Method of
Sequencing Charge
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to integrated circuits, more specifically to a switch mode power converter.
BACKGROUND OF THE INVENTION
As logic integrated circuits (ICs) have migrated to lower working voltages in the search for lower power consumption and higher operating frequencies, and as overall system sizes have continued to decrease, IC power supply designs with smaller size and higher efficiency are in demand. Switch mode power supplies, or DC to DC converters, as they are sometimes called, are frequently used in IC circuits such as digital signal processors (DSPs) and mixed signal analog circuits, etc., to efficiently convert an input supply voltage to voltage levels appropriate for internal circuitry as well as external circuitry that the IC is coupled to. For instance, a 2.8 volt supply voltage provided to a BiCMOS IC may need to be increased internally to 5.0 volts to operate internal CMOS circuitry. As appliances and circuit designs have continued to decrease in size, the need for smaller and more efficient IC switch mode power converters has increased.
FIG. 1
illustrates a block diagram of a buck topology switch mode power converter
10
of the prior art. Control circuit X
3
alternately turns on gate drivers X
1
and X
2
. When driver X
2
is off, the gate of Field Effect Transistor (FET) MN
2
is connected to ground
12
. FETs MN
1
and MN
2
are typically N-channel MOSFETs, for example. When X
2
is on, the gate of FET MN
2
is tied to V
driver
, turning on FET MN
2
. When driver X
1
is off, FET MN
1
is connected to ground
12
, turning off FET MN
1
. In some prior art buck topology converters, when driver X
1
is off, FET MN
1
is connected to the source of FET MN
1
, which has the same effect as the circuit topology shown.
When driver X
1
is on, the gate of FET MN
1
is connected to the upper plate
14
of C
boot
. Capacitor C
boot
is adapted to have some positive voltage stored on it, V
boot
. The lower plate
16
of capacitor C
boot
is coupled to the source of FET MN
1
, and by this means, the gate of FET MN
1
is pulled up to voltage V
boot
above the source of FET MN
1
. Therefore, FET MN
1
is turned on, even as the source of FET MN
1
rises. Before FET MN
1
is turned on, the source of FET MN
1
is pulled to ground by FET MN
2
: FET MN
2
is then turned off and FET MN
1
is turned on. As a result, the source of FET MN
1
rises to the voltage V
in
and the gate of FET MN
1
rises to (V
in
+V
boot
). The use of the “bootstrap capacitor” or boot capacitor C
boot
is a feedback technique which tends to improve linearity and input impedance of circuits operating over a wide range of input signals. Specifically, the boot capacitor C
boot
allows FET MN
1
to be turned on without there being a permanent supply available which is high enough to hold FET MN
1
on even when the source of FET MN
1
is at V
in
.
When FET MN
1
is turned off and FET MN
2
is turned on again, the source of FET MN
1
returns to ground; however, some charge has been taken off boot capacitor C
boot
, so its voltage V
boot
is lower than before. The voltage V
boot
on boot capacitor C
boot
needs to be restored to its previous value. In the prior art circuit
10
shown, the restoration of boot capacitor C
boot
is accomplished by diode D
1
that is connected between voltage V
driver
and the upper plate
14
of boot capacitor C
boot
.
FIG. 2
is a block diagram of a charge pump of the prior art typically used to generate the voltage V
driver
for the circuit
10
shown in
FIG. 1
from supply voltage V
in
. The capacitor C
pump
is first charged to voltage V
in
by closing switches S
1
and S
3
, with switches S
2
and S
4
open. Next, switch S
1
and S
3
are opened, and switches S
2
and S
4
are closed. Some of the charge stored in capacitor C
pump
is pumped into capacitor C
driver
. When switches S
2
and S
4
are closed, the voltage at node A is slightly higher than the voltage at V
driver
, which is caused by the voltage drop across switch S
4
, created by the current flowing from capacitor C
pump
to capacitor C
driver
.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a circuit and method of restoring a charge to a boot capacitor of a switch mode power converter to an amount substantially equal to the amount of the driver voltage, V
driver
.
In a first embodiment, a switch mode power converter circuit is adapted to receive a driver voltage, including a boot capacitor and means for restoring the charge to a boot capacitor to a voltage substantially equal to the driver voltage, where the restoring means is internal to the circuit. The restoring means may include synchronous rectifier which restores the boot capacitor to a voltage equal to the driver voltage less the voltage V
S5
across the synchronous rectifier S
5
. Alternatively, the restoring means may include a synchronous rectifier and a first switch of a charge pump circuit that restore the charge to the boot capacitor in parallel to a voltage equal to the driver voltage less the voltage across the synchronous rectifier plus the voltage across the first switch.
In a second embodiment, a switch mode power converter circuit is adapted to receive an input voltage and generate a driver voltage. The circuit includes a charge pump circuit providing a driver voltage, and the charge pump includes at least a first switch and a first transistor. The circuit also includes a buck converter having a boot capacitor coupled at least to the first switch and the first transistor of the charge pump circuit. The first switch and the first transistor are adapted to recharge the boot capacitor in parallel to a boot voltage in an amount substantially equal to the driver voltage. The boot voltage is equal to the driver voltage less the voltage across the first transistor plus the voltage across the first switch.
Also disclosed is a method of restoring a charge to a boot capacitor of a switch mode power converter circuit, where the circuit is adapted to receive an input voltage and generate a driver voltage. The method includes the step of restoring the charge to the boot capacitor. The restored charge of the boot capacitor is substantially equal to the driver voltage, and the restoring means is internal to the circuit.


REFERENCES:
patent: 4803612 (1989-02-01), Skovmand
patent: 5627460 (1997-05-01), Bazinet et al.
patent: 5818209 (1998-10-01), Masini et al.

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