Datasheet

LTC3816
37
3816f
applicaTions inForMaTion
Therefore R
SER
is calculated to be 13.99k and standard
value R
SER
= 14k is used. Next, the resistor R
AVPDCRN
value
is obtained from the AVP slope requirement:
A mV A
R R R
R
R
AVP
SER PAR NTC
AVPDCRN
DCR=
= =
+
( )




⇒
3 /
||
•
RR
k k k
mV A
m k
AVPDCRN
=
+
( )




=
14 10 10
3
1 3 8 233
||
/
• . .Ω
Select the standard value 8.25k. The capacitor value C
VDCRN
is given by the following equation:
C
L
R R R R
µH
k
VDCRN
SER PAR NTC DCR
=
+
( )




=
+
|| •
.0 33
14 10
kk k m
nF
|| • .
.
10 1 3
13 36
( )




=
Ω
Use the standard value C
VDCRN
= 15nF.
To program the I
MON
voltage, first select the resistor
R
PREIMON
such that I
PREIMON
bias current is around 10µA
to 20µA:
R
I R
I
R
R
PREIMON
LOAD MAX DCR
PREIMON
NTCNET
AVPDCR
=
( )
•
•
NN
A m
µA
k k k
k
k
=
+
( )




=
27 1 3
15
14 10 10
8 25
5 389
• .
•
||
.
.
Ω
Select a standard value R
PREIMON
= 5.1k. Once the resistor
R
PREIMON
value is chosen, the R
IMON
resistor value can
be obtained from the following equation:
R
V R
I R
R
IMON
IMON PREIMON
LOAD MAX DCR
AVPDCR
=
( )
•
• •
•
( )
3
NN
NTCNET
R
V k
A m
k
k k
=
( )
+
1 0 5 1
3 27 1 3
8 25
14 10
. • .
• • .
•
.
||
Ω
110
21 03
k
k
( )




= .
Select R
IMON
= 21k. The value of C
IMON
is selected to
satisfy the desired I
MON
time constant:
C
t
R
µs
k
nF
IMON
IMON
IMON
= = =
300
21
14 28.
Select C
IMON
= 15nF.
The power MOSFETs chosen for this application are the
Renesas RJK0305DPB (top) and 2 × RJK0330DPB (bot-
tom). The upper MOSFET, which is optimized for low
switching losses, has a typical R
DS(ON)
of 10mΩ at V
GS
= 4.5V, a total gate charge of 8nC, and a minimum BV
DSS
of 30V. The bottom MOSFET which is optimized for low
on-resistance, has a typical R
DS(ON)
of 2.8mΩ at V
GS
=
4.5V, a total gate charge of 27nC, and a minimum BV
DSS
of 30V.
From the RJK0305DPB upper MOSFET data sheet, the
Miller capacitance is calculated to be:
C
Q
V
nC
V
pF
MILLER
G
DS
≈ = =
∆
∆
2
12
167
Assuming a top MOSFET junction temperature of 75°C,
δ = 0.25 and the power dissipation in this MOSFET is:
P
V
V
I R t
V
I
MAIN
OUT
IN
LOAD MAX DS ON
IN
=
( )
+
( )
+
( )
( ) ( )
2
2
1 δ
LLOAD MAX
DR MILLER
INTVCC GS MIL G
R C
V V V
( )
( )
•
–
2
1 1
( )( )
+
SS MIL
OSC
MAIN
f
P
V
V
A
( )
.
.








( )
=
( )
+
0 75
12
27 1 0 25
2
(( )
+
( ) ( )( )
+



10
12
27
2
2 6 167
1
5 2 3
1
3
2
m
V
A
pF
V V V
Ω
Ω. •
. –



( )
= + ≈
400
0 57 0 266 0 836
kHz
P W W W
MAIN
. . .