Short circuit current ratcheting in switch mode dc/dc voltage regulators

Abstract

A regulator with a high side pass device and a low side pass device coupled in series to the high side pass device is disclosed. The apparatus further includes a control module coupled to the high side pass device and the low side pass device. The control module is coupled to the high side pass device and the low side pass device to control the high side pass device and the low side pass device. The control module is operable to lock out the high side pass device under certain conditions.

1 . A method implemented on a DC/DC switch mode voltage regulator with a high side pass device and a low side pass device, the method comprising:
 detecting an over current condition over a current limit on the high side pass; and   if the over current condition is detected, locking out the high side pass device and turning on the low side pass device until a second current limit located on the low side pass device is reached.   
     
     
         2 . The method of  claim 1 , further comprising:
 detecting an over current condition over a lower current limit;   and   if the over current condition over the lower current limit is detected, locking out the high side pass device and turning on the low side pass device until a reset signal is received.   
     
     
         3 . The method of  claim 2 , further comprising:
 resetting the DC/DC switch mode voltage regulator, the resetting providing the reset signal.   
     
     
         4 . The method of  claim 3 , further comprising:
 providing power through the high side pass device.   
     
     
         5 . The method of  claim 4 , further comprising:
 operating the DC/DC switch mode voltage regulator responsive to an enable signal.   
     
     
         6 . An apparatus, comprising:
 a high side pass device;   a low side pass device coupled in series to the high side pass device;   a control module coupled to the high side pass device and the low side pass device, the control module coupled to the high side pass device and the low side pass device to control the high side pass device and the low side pass device;   a first resistor coupled in series with the high side pass device and the low side pass device;   a first comparator coupled in parallel with the first resistor, the first comparator having a threshold voltage input differential corresponding to a first current limit, an output of the first comparator coupled to the control module;   a second comparator coupled to sense current of the high side pass device as a voltage, the second comparator having a threshold voltage input differential corresponding to a second current limit, an output of the second comparator coupled to the control module, the second current limit higher than the first current limit;   and   wherein the control module is operable to lock out the high side pass device responsive to the output of the first comparator until a reset signal is received and is operable to lock out the high side pass device responsive to the output of the second comparator until a low current signal is received.   
     
     
         7 . The apparatus of  claim 6 , further comprising:
 a second resistor coupled in series to the low side pass device;   and   a third comparator coupled in parallel with the second resistor, an output of the third comparator coupled to the control module, the output of the third comparator constituting a low current signal.   
     
     
         8 . The apparatus of  claim 7 , further comprising:
 an enable input coupled to the control module;   and   wherein the control module is operable to operate the high and low side pass devices responsive to the enable signal.   
     
     
         9 . The apparatus of  claim 6 , wherein:
 the high side pass device and the low side pass device are power MOSFETs.   
     
     
         10 . The apparatus of  claim 6 , wherein:
 inputs of the second comparator are coupled in parallel with the low side pass device.   
     
     
         11 . The apparatus of  claim 6 , wherein:
 inputs of the second comparator are coupled in parallel with the first resistor.   
     
     
         12 . The apparatus of  claim 8 , further comprising:
 a first external input to the apparatus coupled to the control module, the input to receive a voltage from a resistive divider coupled to a load of the apparatus.   
     
     
         13 . The apparatus of  claim 12 , further comprising:
 a second external input to the apparatus coupled to the control module, the input to receive a voltage from a resistor and capacitor coupled in series.   
     
     
         14 . The apparatus of  claim 13 , further comprising:
 an oscillator coupled to the output of the first comparator to mix the output of the first comparator with an output signal of the oscillator, with the mixed signal provided to the control module.   
     
     
         15 . The apparatus of  claim 14 , further comprising:
 a comparator having a first input and a second input, the first input coupled to the mixed signal and the second input coupled to the first external input, an output of the comparator coupled to the control module.   
     
     
         16 . A DC/DC switch mode voltage regulator with a high side pass device and a low side pass device comprising:
 means for detecting an over current condition over a current limit on the high side pass; and   if the over current condition is detected, means for locking out the high side pass device and turning on the low side pass device until a second current limit located on the low side pass device is reached.   
     
     
         17 . The apparatus of  claim 16 , wherein
 the means for detecting includes a sense element and a finite current level comparator to determine an over current condition.   
     
     
         18 . The apparatus of  claim 16 , further comprising:
 a means for determining when the over current condition has been removed.   
     
     
         19 . The apparatus of  claim 16 , further comprising:
 a latch for overriding the control of a PWM system to keep the high side pass device off and keep the low side pass device on.   
     
     
         20 . The apparatus of  claim 16 , further comprising:
 means for enabling the DC/DC switch mode voltage regulator.