lt3782aeufd Linear Technology Corporation, lt3782aeufd Datasheet - Page 10

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

LT3782A
APPLICATIONS INFORMATION
then R
be 1V, with V
= 32.5k (see Figure 3).
Duty Cycle Limit
When DCL pin is shorted to R
quency is less than 250kHz (R
duty cycle of LT3782A will be at least 90%. The maximum
duty cycle can be clamped to 50% by grounding the DCL
pin or to 75% by forcing the V
resistor divider from R
pin input current is 0.2μA.
Slope Compensation
The LT3782A is designed for high voltage and/or high
current applications, and very often these applications
generate noise spikes that can be picked up by the cur-
rent sensing amplifi er and cause switching jitter. To avoid
switching jitter, careful layout is absolutely necessary to
minimize the current sensing noise pickup. Sometimes
increasing slope compensation to overcome the noise
can help to reduce jitter. The built-in slope compensa-
tion can be increased by adding a resistor R
SLOPE pin to ground. Note that smaller R
slope compensation and the minimum R
R
10
FREQ
/2.
FREQ1
RSET
+ R
FREQ2
= 2.3V then R
should be 80k and V
SET
pin to ground. The typical DCL
FREQ
SET
DCL
FREQ1
pin and switching fre-
voltage to 1.2V with a
> 80k), the maximum
= 47.5k and R
SLOPE
SLOPE
DELAY
SLOPE
allowed is
increases
Figure 3. Increase Delay Time
R
R
should
FREQ1
FREQ2
47.5k
32.5k
FREQ2
from
DELAY
R
Layout Considerations
To prevent EMI, the power MOSFETs and input bypass
capacitor leads should be kept as short as possible. A
ground plane should be used under the switching circuitry
to prevent interplane coupling and to act as a thermal
spreading path. Note that the bottom pad of the package
is the heat sink, as well as the IC signal ground, and must
be soldered to the ground plane.
In a boost converter, the conversion gain (assuming 100%
effi ciency) is calculated as (ignoring the forward voltage
drop of the boost diode):
where D is the duty ratio of the main switch. D can then
be estimated from the input and output voltages:
SET
LT3782A
D=1−
V
V
OUT
3782A F03
IN
=
V
V
1−D
OUT
IN
1
; D
MAX
=1−
V
IN(MIN)
V
OUT
3782af