LTC3829EFE#PBF Linear Technology, LTC3829EFE#PBF Datasheet - Page 22

• Manufacturer Part Number: LTC3829EFE#PBF
• Description: IC BUCK SYNC ADJ 38TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3829EFE#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 5 V
• Frequency - Switching: 250kHz ~ 770kHz
• Voltage - Input: 4.5 ~ 38 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 38-TSSOP Exposed Pad, 38-eTSSOP, 38-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -

LTC3829
applicaTions inForMaTion
Power MOSFET and Schottky Diode
(Optional) Selection
At least two external power MOSFETs must be selected for
each of the three output sections: One N-channel MOSFET
for the top (main) switch and one or more N-channel
MOSFET(s) for the bottom (synchronous) switch. The
number, type and on-resistance of all MOSFETs selected
take into account the voltage step-down ratio as well as
the actual position (main or synchronous) in which the
MOSFET will be used. A much smaller and much lower
input capacitance MOSFET should be used for the top
MOSFET in applications that have an output voltage that
is less than 1/3 of the input voltage. In applications where
V
less important for overall efficiency than its input capaci-
tance at operating frequencies above 300kHz. MOSFET
manufacturers have designed special purpose devices that
provide reasonably low on-resistance with significantly
reduced input capacitance for the main switch application
in switching regulators.
The peak-to-peak MOSFET gate drive levels are set by the
voltage, V
MOSFETs in most applications. Pay close attention to the
BV
logic-level MOSFETs are limited to 30V or less. Selection
criteria for the power MOSFETs include the on-resistance,
R
output current. MOSFET input capacitance is a combination
of several components but can be taken from the typical
gate charge curve included on most data sheets (Figure 9).
The curve is generated by forcing a constant input current
into the gate of a common source, current source loaded
stage and then plotting the gate voltage versus time.

IN
DS(ON)
DSS
>> V
V
GS
specification for the MOSFETs as well; many of the
, input capacitance, input voltage and maximum
OUT
C
CC
MILLER
, the top MOSFETs’ on-resistance is normally
a
Figure 9. Gate Charge Characteristic
, requiring the use of logic-level threshold
MILLER EFFECT
= (Q
Q
IN
B
– Q
A
)/V
b
DS
V
+
GS
–
V
+
–
3729 F09
V
DS
V
IN
The initial slope is the effect of the gate-to-source and
the gate-to-drain capacitance. The flat portion of the
curve is the result of the Miller multiplication effect of the
drain-to-gate capacitance as the drain drops the voltage
across the current source load. The upper sloping line is
due to the drain-to-gate accumulation capacitance and
the gate-to-source capacitance. The Miller charge (the
increase in coulombs on the horizontal axis from a to b
while the curve is flat) is specified for a given V
voltage, but can be adjusted for different V
multiplying the ratio of the application V
specified V
is to take the change in gate charge from points a and b
on a manufacturer’s data sheet and divide by the stated
V
lection criteria for determining the transition loss term in
the top MOSFET but is not directly specified on MOSFET
data sheets. C
definitions of these parameters are not included. When the
controller is operating in continuous mode the duty cycles
for the top and bottom MOSFETs are given by:
The power dissipation for the main and synchronous
MOSFETs at maximum output current are given by:
DS
Main Switch Duty Cycle
P
Synchronous Switc
P
SYNC
MAIN
voltage specified. C
=
=
( )




DS
V
V
V
V
IN
V
IN
OUT
CC
values. A way to estimate the C
IN
RSS
2 2
–
V
–
IN

 
V

 
1
V
I
OUT
and C
I
MAX
TH IL
MAX
2
N
( )

 
h h Duty Cycle

 

 
MILLER
I
OS
MAX
(
+
2
R
N
=
(
V
DR
are specified sometimes but
1 δ
T T H IL
+
V

  
V
1
OUT
)(
2
( )
is the most important se-
IN
(
)
C
1 δ R
R
MILLER
+




DS ON
=
•
(
f

 
)
V
DS ON
IN
)
)
DS
+
•
DS
(
–
V
to the curve
IN
MILLER
V
voltages by
)
OUT
DS

 
drain
term
3829f