7.3.3 Configuring Peak and Hold Currents

I_PEAK and I_HOLD depend on fixed resistance values R_PEAK and R_HOLD as shown in Figure 4. If the PEAK pin or HOLD pin is connected to ground or R_PEAK or R_HOLD is less than 43.33 kΩ (typical), then I_PEAK is at its default value of 300 mA for I_PEAK and 50 mA for I_HOLD.

The I_PEAK value can alternatively be set by connecting an external resistor to ground from the PEAK pin. For example, if a 60-kΩ (= R_PEAK) resistor is connected between PEAK and GND, and R_SENSE = 1 Ω, then the externally set I_PEAK level will be 900 mA. If R_PEAK = 200 kΩ and R_SENSE = 1 Ω, then the externally set I_PEAK level will be 300 mA. TI does not recommend using a resistor from 30 kΩ and 55 kΩ to avoid the I_PEAK or I_HOLD current slipping from the maximum current setting to the default setting.

In case R_SENSE = 2 Ω instead of 1 Ω, then I_PEAK = 450 mA (when R_PEAK = 55 kΩ) and I_PEAK = 150 mA (when R_PEAK = 200 kΩ). In the 8-pin package, the HOLD reference uses the internal V_REF setting of 50 mV. In the 14-pin package, external setting of the HOLD current, I_HOLD, works in the same way as the external setting for I_PEAK but the current levels are 1/6 of the I_PEAK levels for the same resistor setting.

External settings for I_PEAK and I_HOLD are independent of each other. If R_PEAK or R_HOLD is decreased below 33.33 kΩ (typical value), then the reference is clamped to the internal setting of 300 mV for PEAK and 50 mV for HOLD. Use Equation 2 and Equation 3 to calculate the values for I_PEAK and I_HOLD respectively.

The currents and resistor values should be chosen such that the voltage across the sense resistor is more than 30 mV.

Equation 2.

Equation 3.

Figure 4. I_PEAK and I_HOLD settings for R_SENSE = 1 Ω