ZHCS819G March 2012 – March 2018 DRV110
With the selected peak current, hold current, and peak keep time values, the values of RPEAK, RHOLD (for 14-pin package), CKEEP, and RSENSE can be determined. Table 4 lists the example values and results from calculation.
|VARIABLE||VALUE||14-PIN VALUES||8-PIN VALUES||CALCULATED FROM|
|Peak current||150 mA||RPEAK = 400 kΩ||RPEAK = 400 kΩ||Equation 2|
|Hold current||50 mA||RHOLD = 200 kΩ or
connect HOLD to ground
|Keep time||100 ms||CKEEP = 1 µF||CKEEP = 1 µF||Equation 1|
|PWM frequency||20 kHz||ROSC = Shorted to ground||ROSC = Shorted to ground||Equation 4|
Use Equation 2 and Equation 3 to calculate the values of the RPEAK resistor and RHOLD (if applicable) resistor. For the sample values, the RPEAK resistor is set to 400 kΩ and the RHOLD resistor is shorted to GND. TI recommends using a 0-Ω resistor for prototyping in case changes to this value are desired.
Next, select the value of the CKEEP capacitor based on Equation 1. For the sample value, the CKEEP capacitor is set to 1 µF. The ROSC resistor is initially be shorted to GND, but a 0-Ω resistor is also recommended for prototyping. Additionally, a low-pass filter on the SENSE line can be added in a high-noise environment and is recommended for prototyping. The typical value for the low pass filter resistor is 1 kΩ and the typical value for the filter capacitor is 100 pF.
The value of sense resistor can be selected based on the preference of the designer. The only restriction is that the voltage across the sense resistor (found by the RSENSE resistance times the IHOLD current) must be greater than 30 mV for reliable operation.
The external FET and current recirculation diode must be selected based on the current values defined in Table 4 and the supply voltage. The current recirculation diode should be a fast recovery diode.