Switching converter with valley current detection

1 . A DC/DC converter comprising a low side and a high side, the converter comprising:

a first switching device being part of the low side, the first switching device comprising a first resistance and first channel;

a low side current generator configured to generate a low side current flowing in the first switching device;

a second switching device, the second switching device comprising a second resistance and a second channel;

a compensation resistor coupled in series to the second switching device;

a valley current reference current generator configured to generate a valley current threshold current flowing in the second switching device and in the compensation resistor for obtaining a first voltage value, the compensation resistor is designed to have a value based on:

the first resistance and second resistance,

a fraction of a designed current that flows in the first channel, or

a fraction of a designed value of the valley current threshold current that flows in the second channel; and

a comparator configured to compare the first voltage value and a reference voltage for generating an error signal as a function of the comparison, the error signal controlling a conductivity of the first switching device of the low side.

2 . The DC/DC converter of claim 1 , wherein a resistance value R 1 of the compensation resistor is defined by:

R

1

≈

α

·

R

ds

,

LS

′

w

sd2

-

β

·

R

ds

,

sd2

′

w

sd2

,

where α is a percentage of current flowing through the first switching device which is flowing through the first channel,

where R′ ds,LS is a drain to source resistance of the first switching device,

where w sd2 is a width of the second switching device,

where β is a percentage of current flowing through the second switching device which is flowing through the second channel, and

where R′ ds,sd2 is a drain to source resistance of the second switching device.

3 . The DC/DC converter of claim 1 , wherein a resistance value of the compensation resistor monotonically increases with increasing temperature of the compensation resistor.

4 . The DC/DC converter of claim 1 , wherein a resistance value of the compensation resistor is between at least one of: 30Ω and 100Ω, 50Ω and 90Ω, and 60Ω and 80Ω, for T<80° C. and is between at least one of 60Ω and 200Ω, 60Ω and 150Ω, and 70Ω and 140Ω for T>80° C.

5 . The DC/DC converter of claim 1 , wherein a resistance value of the compensation resistor and a resistance value of at least one of the first and second switching devices are temperature dependent with substantially a same resistance divided by temperature slope for T<80° C.

6 . The DC/DC converter of claim 1 , wherein a series resistance of the second switching device and the compensation resistor differs from one divided by a resistance of the first switching device by less than 5%.

7 . The DC/DC converter of claim 6 , wherein the first switching device comprises a first transistor with a first gate configured to receive a first gate voltage, wherein the second switching device comprises a second transistor with a second gate configured to receive a second gate voltage, and wherein the first gate voltage is equal to the second gate voltage.

8 . The DC/DC converter of claim 1 , wherein a series resistance of the second switching device and the compensation resistor differs from a resistance of the first switching device by less than 5% while operating the DC/DC converter in a temperature of 80° C.

9 . The DC/DC converter of claim 1 , wherein the compensation resistor comprises a third switching device.

10 . The DC/DC converter of claim 1 , wherein the first switching device comprises a first transistor with a first gate configured to receive a first gate voltage, wherein the second switching device comprises a second transistor with a second gate configured to receive a second gate voltage, wherein the third switching device comprises a third transistor with a third gate configured to receive a third gate voltage, and wherein the first gate voltage, the second gate voltage, and the third gate voltage are equal.

11 . A converter circuit, comprising:

a high side device coupled to a switch node and configured to selectively electrically couple the switch node to a high input voltage node according to a high side control signal;

a low side device coupled to the switch node and configured to selectively electrically couple the switch node to a low input voltage node according to a low side control signal;

an inductor coupled between the switch node and an output node of the converter circuit;

a first switch and a compensation resistor coupled in series with the first switch;

a comparator configured to compare a reference voltage with a voltage equal to a sum of a voltage at the switch node and a voltage drop across the first switch and the compensation resistor, the comparator being configured to generate a valley current threshold signal based in part on an output of the comparator, the valley current threshold signal indicating that a valley current provided to the inductor falls below a threshold current limit; and

a controller configured to generate, based in part on the valley current threshold signal, the high side control signal and the low side control signal.

12 . The converter circuit of claim 11 , wherein a resistance of the first switch and compensation resistor differs from one divided by a resistance of the low side device by less than 5%.

13 . The converter circuit of claim 11 , wherein the first switch comprises a first transistor with a first gate configured to receive a first gate voltage, wherein the low side device comprises a second transistor with a second gate configured to receive a second gate voltage, and wherein the first gate voltage is equal to the second gate voltage.

14 . The converter circuit of claim 11 , wherein the compensation resistor comprises a second switch.

15 . The converter circuit of claim 14 , wherein the first switch comprises a first gate configured to receive a first gate voltage equal to a gate voltage of the low side device, and wherein the second switch comprises a second gate configured to receive a second gate voltage equal to the gate voltage of the low side device.

16 . The converter circuit of claim 11 , wherein the first switch and the compensation resistor has a first voltage drop, wherein the low side device has a second voltage drop, and wherein the first voltage drop is within 5% of the second voltage drop.

17 . A method of controlling a DC/DC converter, the method comprising:

generating a valley current threshold current to flow in a series connection comprising a first switching device and a compensation resistor, the first switching device comprising a first transistor with a first gate configured to receive a first gate voltage;

generating a first voltage value based on the valley current threshold current and a series resistance of the first switching device and the compensation resistor;

with a comparator, comparing the first voltage value and a reference voltage to generate an error signal based on the comparison; and

controlling a conductivity of a low side switching device of the DC/DC converter based in part on the error signal, wherein the low side switching device comprises a second transistor with a second gate configured to receive a second gate voltage, and wherein the first gate voltage is equal to the second gate voltage.

18 . The method of claim 17 , wherein the compensation resistor comprises a third transistor with a third gate configured to receive a third gate voltage, and wherein the third gate voltage is equal to the first and second gate voltages.

19 . The method of claim 17 , wherein a resistance value of the compensation resistor monotonically increases with increasing temperature of the compensation resistor.

20 . The method of claim 17 , wherein a resistance value of the compensation resistor is between at least one of: 30Ω and 100Ω, 50Ω and 90Ω, and 60Ω and 80Ω, for T<80° C. and is between at least one of 60Ω and 200Ω, 60Ω and 150Ω, and 70Ω and 14Ω for T>80° C.