XRP7714_1009 Datasheet, PDF (27/29 Pages) Exar Corporation – Quad Channel Digital PWM Step Down Controller

XRP7714
Quad Channel Digital PWM Step Down Controller
Power MOSFETs Selection
Selecting MOSFETs with lower Rdson reduces conduction losses at the expense of increased
switching losses. Conduction losses are expressed by the two following equations.
High Side MOSFET Conducted Loss:
Low Side MOSFET Conducted Loss:
P_cond
=
I _out
2
⋅
R_dson
⋅
V_out
V_in
P_cond
=
I2
out
⋅ R_dson
⋅
¹
−
V_out
V_in

The 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.
LAYOUT GUIDELINES
Refer to application note ANP-32 “Practical Layout Guidelines for Power^XR Designs”.
© 2010 Exar Corporation
27/29
Rev. 1.1.4