LTC3829EFE#PBF Linear Technology, LTC3829EFE#PBF Datasheet - Page 29

• 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: -

applicaTions inForMaTion
INTV
The LTC3829 features a true PMOS LDO that supplies power
to INTV
drivers and much of the LTC3829’s internal circuitry. The
LDO regulates the voltage at the INTV
is greater than 5.5V. EXTV
a P-channel MOSFET and can supply the needed power
when its voltage is higher than 4.7V. Each of these can
supply a peak current of 100mA and must be bypassed
to ground with a minimum of 4.7µF ceramic capacitor or
low ESR electrolytic capacitor. No matter what type of bulk
capacitor is used, an additional 0.1µF ceramic capacitor
placed directly adjacent to the INTV
highly recommended. Good bypassing is needed to supply
the high transient currents required by the MOSFET gate
drivers and to prevent interaction between the channels.
High input voltage applications in which large MOSFETs
are being driven at high frequencies may cause the maxi-
mum junction temperature rating for the LTC3829 to be
exceeded. The INTV
gate charge current, may be supplied by either the 5V LDO
or EXTV
than 4.7V, the LDO is enabled. Power dissipation for the
IC in this case is highest and is equal to V
gate charge current is dependent on operating frequency
as discussed in the Efficiency Considerations section.
The junction temperature can be estimated by using the
equations given in Note 3 of the Electrical Characteristics
tables. For example, the LTC3829 INTV
to less than 42mA from a 38V supply in the UHF package
and not using the EXTV
To prevent the maximum junction temperature from be-
ing exceeded, the input supply current must be checked
while operating in continuous conduction mode (MODE
= SGND) at maximum V
T
J
CC
= 70°C + (42mA)(38V)(34°C/W) = 125°C
CC
(LDO) and EXTV
CC
. When the voltage on the EXTV
from the V
CC
IN
current, which is dominated by the
CC
supply. INTV
CC
IN
CC
supply:
. When the voltage applied to
connects to INTV
CC
CC
CC
CC
pin to 5V when V
and PGND pins is
current is limited
powers the gate
IN
CC
• I
INTVCC
CC
pin is less
through
. The
IN
EXTV
and the EXTV
remains on as long as the voltage applied to EXTV
above 4.5V. Using the EXTV
and control power to be derived from one of switching
regulator outputs during normal operation and from the
INTV
up, short circuit). If more current is required through the
EXTV
be added between the EXTV
apply more than 6V to the EXTV
EXTV
Significant efficiency and thermal gains can be realized
by powering INTV
rent resulting from the driver and control currents will be
scaled by a factor of (duty cycle)/(switcher efficiency).
Tying the EXTV
temperature in the previous example from 125°C to:
However, for low voltage outputs, additional circuitry is
required to derive INTV
The following list summarizes the four possible connec-
tions for EXTV
1. EXTV
2. EXTV
3. EXTV
T
to be powered from the internal 5V LDO resulting
in an efficiency penalty of up to 10% at high input
voltages.
connection for a 5V regulator and provides the highest
efficiency.
supply is available, it may be used to power EXTV
providing it is compatible with the MOSFET gate drive
requirements.
J
CC
CC
CC
CC
= 70°C + (42mA)(5V)(34°C/W) = 77°C
when the output is out of regulation (e.g., start-
CC
CC
CC
than is specified, an external Schottky diode can
< V
rises above 4.7V, the INTV
connected to an external supply. If a 5V external
left open (or grounded). This will cause INTV
connected directly to V
IN
.
CC
CC
CC
is connected to the INTV
:
pin to a 5V supply reduces the junction
CC
from the output, since the V
CC
power from the output.
CC
CC
allows the MOSFET driver
CC
and INTV
OUT
pin and make sure that
CC
. This is the normal
LDO is turned off
LTC3829
CC
CC
. The EXTV
pins. Do not
CC
remains

IN
cur-
3829f
CC
CC
CC