XRP7708_12 Datasheet, PDF (26/28 Pages) Exar Corporation – Quad Channel Digital PWM Step Down Controllers

XRP7708 and XRP7740
Quad Channel Digital PWM Step Down Controllers
Total input voltage ripple is the sum of the above:
∆V_Tot = ∆V_Cin + ∆V_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
⋅ ^Vout
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.
LAYOUT GUIDELINES
Refer to application note ANP-32 “Practical Layout Guidelines for Power^XR Designs” and ANP-35
“XRP77XX: Extending the MOSFET Gate Drive Conductors”.
REGISTER MAP
See ANP-31 “PowerXR Configuration and Programming” for details of the register map and other
programming information.
© 2012 Exar Corporation
26/28
Rev. 1.2.2