MAX15014_07 Datasheet, PDF (22/26 Pages) Maxim Integrated Products – 1A, 4.5V to 40V Input Buck Converters with 50mA Auxiliary LDO Regulators

1A, 4.5V to 40V Input Buck Converters with
50mA Auxiliary LDO Regulators
R6
V_IN
R3
4.5V TO 40V
C8
C6
R5
C7
V_IN
R4
5V TO 40V
C_F
PGND SGND
C_SS
1Ω
C_REG
0.47µF
C_{IN_LDO}
C_{IN_SW}
C_DRAIN
D1
IN_LDO
COMP
IN_SW
DRAIN
BST
FB
EN_SW
EN_SYS
C+
C-
SS
SYNC
REG
MAX15015
MAX15016
LX
RESET
CT
LDO_OUT
DVREG
PGND
SET_LDO
SGND
C_BST
L
D2
V_OUT1 AT 1A
C_OUT
10kΩ
V_OUT2 AT 50mA
C_CT
C_{LDO_OUT}
Figure 6. MAX15015/MAX15016 Typical Application Circuit (4.5V to 40V Input Operation)
power dissipated due to the RMS current through the
internal power MOSFET (P_MOSFET). The total power
dissipated in the package must be limited such that the
junction temperature does not exceed its absolute max-
imum rating of +150°C at maximum ambient tempera-
ture. Calculate the power lost in the MAX15014–
MAX15017 using the following equations:
The power loss through the switch:
P_MOSFET = (I_{RMS_MOSFET})2 × R_ON
I_{RMS_MOSFET} =
D
3
×
⎡⎣⎢_I² _PK
+ (I_PK
×I_DC
)
+I²
DC
⎤
⎦⎥
I_PK
= I_OUT
+
∆I_P−P
2
I_DC
= I_OUT
−
∆I_P−P
2
D = ^VOUT
V_IN
R_ON is the on-resistance of the internal power MOSFET
(see the Electrical Characteristics).
The power loss due to switching the internal MOSFET:
P_SW
=
V_IN
×I_OUT
× (t_R
4
+ t_F)× f_SW
t_R and t_F are the rise and fall times of the internal power
MOSFET measured at LX.
The power loss due to the switching supply current (I_SW):
P_Q = V_{IN_ SW} × I_SW
The power loss due to the LDO regulator:
P_LDO = (V_{IN_LDO} − V_{LDO_ OUT}) × I_{LDO_ OUT}
The total power dissipated in the device will be:
P_TOTAL = P_MOSFET + P_SW + P_Q + P_LDO
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