LTC3786 LINER [Linear Technology], LTC3786 Datasheet - Page 34

• Manufacturer Part Number: LTC3786
• Description: Multi-Phase Current Mode Step-Up DC/DC Controller
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
LTC3862-2
8. The power MOSFET chosen for this application is
9. The total IC quiescent current, IC power dissipation
10. The inductor ripple current was chosen to be 40%
11. The maximum current sense threshold for the
34
The inductor value chosen was 57.8μH and the part
number is PA2050-583, manufactured by Pulse Engi-
neering. This inductor has a saturation current rating
of 5A.
a Renesas HAT2267H. This MOSFET has a typical
R
at a minimum of 80V and the maximum continuous
drain current is 25A. The typical gate charge is 30nC
for a V
an absolute maximum avalanche energy rating EAS
of 30mJ, indicating that it is capable of avalanche
without catastrophic failure.
and maximum junction temperature are approximately:
and the maximum load current is 1.5A. For a current
limit set at 30% above the maximum load current, the
maximum switch and sense resistor currents are:
LTC3862-2 is 75mV at low duty cycle and a normalized
slope gain of 1.0. Using Figure 20, the maximum sense
voltage drops to 68mV at a duty cycle of 70% with a
normalized slope gain of 1, so the sense resistor is
calculated to be:
For this application a 20mΩ, 1W surface mount resis-
tor was used for each phase.
I
SW(MAX)
DS(ON)
I
P
T
R
Q(TOT)
J
DISS
SENSE
= 70°C + 504mW • 34°C/W = 87.1°C
GS
of 13mΩ at V
= 24V • 21mA = 504mW
= 10V. Last but not least, this MOSFET has
= I
=
= I
= 3mA + 2 • 30nC • 300kHz = 21mA
=
2
1
R(SENSE)
Q
V
• 1+
SENSE(MAX)
+ 2 • Q
I

 
SW(MAX)
0.4
2
=
G(TOT)
GS
n
1

 
• 1+
•
= 10V. The BV
=

 
1.3 • 1.5A
1– 0.669
• f
68mV
3.5A
χ
2

 
•
= 19.4mΩ
1.3 •I
= 3.5A
1– D
DSS
O(MAX)
MAX
is rated
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 (1.5A/2 = 0.75A), but the peak current
in each diode is:
The diode chosen for this application is the
MURS320T3H, manufactured by ON Semiconductor.
This surface mount diode has a maximum average
forward current of 3A at 140°C and a maximum reverse
voltage of 200V. The maximum forward voltage drop
at 25°C is 0.875V and is 0.71V at 150°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
= 2.7A • 0.71V • (1 – 0.669) = 0.64W
COUT
D(PEAK)
=
=
≤
=
=
= 0.12W
n
1
2
1
0.01• V




 
• 1+
• 1+
• V
I
n • 1– D

 
2 • 1– 0.669

 
D(PEAK)
1.3 •I
F(PEAK)
(
1.3 • 1.5
(
χ
2
0.4
OUT
2
O(MAX)

 
•

 
MAX
1– D
• (1 – D
•
=
I
O(MAX)
1– 0.669
0.01• 72V
)
)
1.5A



MAX

 
2.7A
2
2
• R
• 0.020 • 0.669
MAX
SENSE
)
= 2.7A
= 0.267Ω
• D
MAX
38622f