R2J20751NP Datasheet, PDF (22/26 Pages) Renesas Technology Corp – Peak Current Mode Synchronous Buck Controller with Power MOS FETs

R2J20751NP
V_THR
Vpos
Preliminary
V_THF
Vshare
2. Selecting the external resistors
When the output of phase control comparator becomes low, switching operation of the slave device starts and
operation becomes two phase. According to the results of (11) and (12), VTHR and VTHF are 1.473 V and 0.969 V.
These become the voltages on the POS pins (comparator non-inverted input pin). VTHR is the start-up level for the
slave device and VTHF is the shut-down level for the slave device.
We set the output current of CO at around 100 A when the voltage on Share is 1.379 V. In this case, R5 is:
R5 = (V_CIN – 1.379) / 100 A = 35.27 k
The formulae that express R3 and R4 are:
R3 = R4  R5 / (R4 + R5)  (V_CIN – V_THF) / V_THF = 18.34 k and
R4 = R5  (V_THR – V_THF) / (V_CIN – V_THR) = 5.04 k.
With E24-series resistors, R3 = 18 k, R4 = 5.1 k, and R5 = 36 k.
R07DS0240EJ0100 Rev.1.00
Jan 26, 2011
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