XRP7708 Datasheet, PDF (25/27 Pages) Exar Corporation – Quad Channel Digital PWM Step Down Controller

XRP7708
Quad Channel Digital PWM Step Down Controller
ΔV_Tot = ΔV_Cin + ΔV_ESR
Power MOSFETs Selection
Selecting MOSFETs with lower Rdson reduces conduction losses at the expense of increased
switching losses. A simplified expression for conduction losses is given by:
P_cond
=
I2
out
⋅
R_dson
⋅
V_out
V_in
MOSFET’s junction temperature can be estimated from:
T_j = 2P_cond R_thja + T_ambient
This assumes that the switching loss is the same as the conduction loss. R_thja is the total MOSFET
thermal resistance from junction to ambient.
© 2010 Exar Corporation
25/27
Rev. 1.0.3