Datasheet

Data Sheet ADP1872/ADP1873
Rev. B | Page 29 of 40
Loss Calculations
Duty cycle = 1.8/12 V = 0.15
R
ON (N2)
= 5.4 mΩ
t
BODY(LOSS)
= 20 ns (body conduction time)
V
F
= 0.84 V (MOSFET forward voltage)
C
IN
= 3.3 nF (MOSFET gate input capacitance)
Q
N1, N2
= 17 nC (total MOSFET gate charge)
R
GATE
= 1.5 Ω (MOSFET gate input resistance)
( )
[ ]
2
1
LOAD
N2(ON)N1(ON)N2(CL)N1,
IRDRDP ××−+×=
= (0.15 × 0.0054 + 0.85 × 0.0054) × (15 A)
2
= 1.215 W
2
)(
)(
×× ×=
F
LOAD
SW
LOSSBODY
LOSSBODY
VI
t
t
P
= 20 ns × 300 × 10
3
× 15 A × 0.84 × 2
= 151.2 mW
P
SW (LOSS)
= f
SW
× R
GATE
× C
TOTAL
× I
LOAD
× VIN × 2
= 300 × 10
3
× 1.5 Ω × 3.3 × 10
−9
× 15 A × 12 × 2
= 534.6 mW
( )
[ ]
( )
[ ]
BIAS
DD
lowerFET
SW
DD
BIAS
DR
upperFET
SW
DR
LOSSDR
IVCfV
IVCf
VP
+×
++×=
)(
= (5.12 × (300 × 10
3
× 3.3 × 10
−9
× 5.12 + 0.002)) +
(5.5 × (300 × 10
3
×3.3 ×10
−9
×5.5 + 0.002))
= 77.13 mW
P
COUT
= (I
RMS
)
2
× ESR = (1.5 A)
2
× 1.4 mΩ = 3.15 mW
2
)(
LOAD
LOSSDCR
IDCRP ×=
= 0.003 × (15 A)
2
= 675 mW
P
CIN
= (I
RMS
)
2
× ESR = (7.5 A)
2
× 1 mΩ = 56.25 mW
P
LOSS
= P
N1, N2
+ P
BODY (LOSS)
+ P
SW
+ P
DCR
+ P
DR
+ P
COUT
+ P
CIN
= 1.215 W + 151.2 mW + 534.6 mW + 77.13 mW +
3.15 mW + 675 mW + 56.25 mW
= 2.62 W