8.3.2 Current Sense Comparator

A comparator, two resistors and a current source create a peak current detection circuit block. See the Functional Block Diagram for details. A current source controlled by V_IADJ draws a current across a resistor in series with a comparator, forcing a proportional offset. The resistor in the current source (10 R) and in series with the comparator (R) are sized with a 10:1 ratio. This ratio allows for a practical voltage range of operation for the IADJ pin and maintains a small current sense voltage for low losses and less impact on efficiency.

The ON cycle begins with the offset in place via IADJ across the resistor R at the VIN pin. When the current rises enough to create a voltage across the sense resistor to match the offset, the comparator trips. The end of the ON-time period starts an OFF-time cycle.

Trace resistance can have an impact on accuracy, be careful when routing the traces to VIN and CSN from the sense resistor. Because the sense resistor value is typically in milli-ohms, use a short kelvin connection to CSN and place the sense resistor as close as possible to VIN.