lt3782aeufd Linear Technology Corporation, lt3782aeufd Datasheet - Page 14

• Manufacturer Part Number: lt3782aeufd
• Description: 2-phase Step-up Dc/dc Controller
• Manufacturer: Linear Technology Corporation

LT3782A
APPLICATIONS INFORMATION
For a given V
and then derive the output RMS ripple current from Figure
6. After choosing output capacitors with suffi cient RMS
ripple current rating, we also need to consider the ESR
requirement if electrolytic caps, tantulum caps, POSCAPs
or SP CAPs are selected. Given the required output ripple
voltage spec ΔV
ripple current ΔI
the output capacitor to be
External Regulator to Bias Gate Drivers
For applications with V
may get too high. To reduce heat, an external regulator
between 12V to 14V should be used to override the internal
V
and BGATE2 (see Figure 7).
Effi ciency Considerations
The effi ciency of a switching regulator is equal to the out-
put power divided by the input power (¥100%). Percent
effi ciency can be expressed as:
where L1, L2, etc. are the individual loss components
as a percentage of the input power. It is often useful to
analyze individual losses to determine what is limiting
the effi ciency and which change would produce the most
14
GBIAS
% Effi ciency = 100% – (L1 + L2 + L3 + …),
ESR ≤
regulator to supply the current needed for BGATE1
ΔV
ΔI
OUT
IN
OUT
and V
OUT
OUT
(in RMS value) and the calculated RMS
, one can estimate the ESR value of
OUT
IN
, we can calculate the duty cycle D
higher than 24V, the IC temperature
3782A F07
LT3782A
GBIAS1
GBIAS2
GBIAS
Figure 7
2μF
improvement. Although all dissipative elements in the
circuit produce losses, four main sources usually account
for the majority of the losses in LT3782A application
circuits:
1. The supply current into V
2. Power MOSFET switching and conduction losses:
of the DC supply current I
acteristics) and the MOSFET driver and control currents.
The DC supply current into the V
7mA and represents a small power loss (much less
than 1%) that increases with V
results from switching the gate capacitance of the power
MOSFET; this current is typically much larger than the
DC current. Each time the MOSFET is switched on and
then off, a packet of gate charge Q
GBIAS to ground. The resulting dQ/dt is a current that
must be supplied to the GBIAS capacitor through the
V
12V
IN
I
P
P
Q(TOT)
+
pin by an external supply. In normal operation:
IC
FET
= V
+ k • V
=
IN
≈ I
1– D
I
O(MAX)
• (I
Q
O
= f • Q
2
2
Q
MAX
•
+ f • Q
1– D
I
O(MAX)
G
2
2
• R
MAX
G
)
IN
Q
DS(ON)
(given in the Electrical Char-
. The V
• C
RSS
IN
IN
• D
IN
G
pin is typically about
. The driver current
• f
MAX
is transferred from
current is the sum
•
T
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