LTC3862 LINER [Linear Technology], LTC3862 Datasheet - Page 33

• Manufacturer Part Number: LTC3862
• Description: Multi-Phase Current Mode Step-Up DC/DC Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
8. The power MOSFET chosen for this application is
9. The total IC quiescent current, IC power dissipation and
10. The inductor ripple current was chosen to be 40%
11. The maximum current sense threshold for the LTC3862
The inductor value chosen was 18.7μH and the part
number is PB2020-223, manufactured by Pulse Engi-
neering. This inductor has a saturation current rating
of 20A.
a Renesas HAT2266H. This MOSFET has a typical
R
= 10V. The BV
the maximum continuous drain current is 30A. The
typical gate charge is 25nC for a V
not least, this MOSFET has an absolute maximum
avalanche energy rating EAS of 34mJ, indicating that it
is capable of avalanche without catastrophic failure.
maximum junction temperature are approximately:
and the maximum load current is 5A. For a current
limit set at 30% above the maximum load current, the
maximum switch and sense resistor currents are:
is 75mV at low duty cycle and a normalized slope gain
of 1.0. Using Figure 20, the maximum sense voltage
drops to 73mV at a duty cycle of 51% with a normal-
ized slope gain of 1, so the sense resistor is calculated
to be:
For this application a 8mΩ, 1W surface mount resistor
was used for each phase.
I
SW MAX
DS(ON)
I
P
T
R
Q(TOT)
(
J
DISS
SENSE
= 70°C + 432mW • 34°C/W = 84.7°C
of 11mΩ at V
)
= 24V • 18mA = 432mW
= I
= 3mA + 2 • 25nC • 300kHz = 18mA
=
=
=
I
2
1
Q
R SENSE
V
(
DSS
•
+ 2 • Q
SENSE MAX
I
⎛
⎝ ⎜
SW MAX
1
+
is rated at a minimum of 60V and
(
)
0 4
(
G(TOT)
2
=
.
GS
)
n
1
⎞
⎠ ⎟
)
•
= 4.5V and 9.2mΩ at V
•
=
⎛
⎝ ⎜
1 0 505
• f
1 3 5
1
– .
73
. •
7 9
+
.
mV
χ
2
A
GS
⎞
⎠ ⎟
A
•
=
= 4.5V. Last but
1 3
=
9 2 Ω
. •
1
.
7 9
–
.
m
D
I
O MAX
A
MAX
(
) )
GS
12. The power dissipated in the sense resistors in current
13. The average current in the boost diodes is half the
14. Two types of output capacitors are connected in paral-
limit is:
output current (5A/2 = 2.5A), but the peak current in
each diode is:
The diode chosen for this application is the 30BQ060,
manufactured by International Rectifi er. This surface
mount diode has a maximum average forward current
of 3A at 125°C and a maximum reverse voltage of 60V.
The maximum forward voltage drop at 25°C is 0.65V
and is 0.42V at 125°C (the positive TC of the series
resistance is compensated by the negative TC of the
diode forward voltage).
The power dissipated by the diode is approximately:
lel for this application; a low ESR ceramic capacitor
and an aluminum electrolytic for bulk storage. For
a 1% contribution to the total ripple voltage, the
maximum ESR of the composite output capacitance
is approximately:
P
P
I
ESR
D PEAK
R SENSE
D
(
(
= I
= 6.06A • 0.42V • (1 – 0.505) = 1.26W
COUT
D(PEAK)
)
=
=
)
≤
=
= .
=
n
2
1
1
⎛
⎜
⎝
0 20
⎛
⎜
⎝
0 01
•
•
• V
.
n
2 1 0 505
⎛
⎝ ⎜
⎛
⎝ ⎜
I
1 3
D PEAK
1
1
• –
• – .
(
. •
F(PEAK)
+
+
(
(
W
•
1 3 5
1
V
χ
0
. •
2
I
2
OUT
O MAX
. .
⎞
⎠ ⎟
D
4
)
(
MAX
•
⎞
⎠ ⎟
• (1 – D
1
•
=
I
O MAX
–
1 0 505
)
(
0 01 48
)
D
)
– .
⎞
⎟
⎠
.
⎞
⎟
⎠
MAX
5
2
4 4
2
A
•
MAX
.
)
• .
•
LTC3862
R
0 009 0 50
A
SEN
)
V
=
S S E
6 06
=
• .
.
•
0 10
D
33
.
A
MAX
3862fb
9 9 Ω
5 5