LTC3727EG-1#TR Linear Technology, LTC3727EG-1#TR Datasheet - Page 17

• Manufacturer Part Number: LTC3727EG-1#TR
• Description: IC REG SW SYNC 2PH STPDWN 28SSOP
• Manufacturer: Linear Technology
• Series: PolyPhase®r
• Type: Step-Down (Buck)r

Specifications of LTC3727EG-1#TR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.8 ~ 14 V
• Current - Output: 25A
• Frequency - Switching: 250kHz ~ 550kHz
• Voltage - Input: 4 ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
INTV
An internal P-channel low dropout regulator produces
7.5V at the INTV
powers the drivers and internal circuitry within the
LTC3727. The INTV
current of 50mA and must be bypassed to ground with a
minimum of 4.7μF tantalum, 10μF special polymer, or low
ESR type electrolytic capacitor. A 1μF ceramic capacitor
placed directly adjacent to the INTV
is highly recommended. Good bypassing is necessary to
supply the high transient currents required by the MOSFET
gate drivers and to prevent interaction between channels.
Higher input voltage applications in which large MOSFETs
are being driven at high frequencies may cause the maxi-
mum junction temperature rating for the LTC3727 to be
exceeded. The system supply current is normally domi-
nated by the gate charge current. Additional external
loading of the INTV
needs to be taken into account for the power dissipation
calculations. The total INTV
either the 7.5V internal linear regulator or by the EXTV
input pin. When the voltage applied to the EXTV
less than 7.3V, all of the INTV
internal 7.5V linear regulator. Power dissipation for the IC
in this case is highest: (V
is lowered. The gate charge current is dependent on
operating frequency as discussed in the Efficiency Consid-
erations section. The junction temperature can be esti-
mated by using the equations given in Note 2 of the
Electrical Characteristics. For example, the LTC3727 V
current is limited to less than 24mA from a 24V supply
when not using the EXTV
Use of the EXTV
ture to:
Dissipation should be calculated to also include any added
current drawn from the internal 3.3V linear regulator. To
prevent maximum junction temperature from being ex-
ceeded, the input supply current must be checked operat-
ing in continuous mode at maximum V
T
T
J
J
CC
= 70°C + (24mA)(24V)(95°C/W) = 125°C
= 70°C + (24mA)(7.5V)(95°C/W) = 87°C
Regulator
CC
CC
input pin reduces the junction tempera-
U
pin from the V
CC
CC
pin regulator can supply a peak
IN
and 3.3V linear regulators also
CC
)(I
U
CC
INTVCC
pin as follows:
CC
current can be supplied by
current is supplied by the
), and overall efficiency
IN
W
CC
supply pin. INTV
and PGND IC pins
IN
.
U
CC
pin is
CC
CC
IN
EXTV
The LTC3727 contains an internal P-channel MOSFET
switch connected between the EXTV
When the voltage applied to EXTV
internal regulator is turned off and the switch closes,
connecting the EXTV
supplying internal power. The switch remains closed as
long as the voltage applied to EXTV
This allows the MOSFET driver and control power to be
derived from the output during normal operation (7.2V <
V
output is out of regulation (start-up, short-circuit). If more
current is required through the EXTV
specified, an external Schottky diode can be added be-
tween the EXTV
than 8.5V to the EXTV
Significant efficiency gains can be realized by powering
INTV
from the driver and control currents will be scaled by a
factor of (Duty Cycle)/(Efficiency). For 7.5V regulators this
supply means connecting the EXTV
However, for 3.3V and other lower voltage regulators,
additional circuitry is required to derive INTV
from the output.
The following list summarizes the four possible connec-
tions for EXTV
1. EXTV
to be powered from the internal 7.5V regulator resulting in
an efficiency penalty of up to 10% at high input voltages.
2. EXTV
connection for a 7.5V regulator and provides the highest
efficiency.
3. EXTV
supply is available in the 7.5V to 8.5V range, it may be used
to power EXTV
MOSFET gate drive requirements.
4. EXTV
work. For 3.3V and other low voltage regulators, efficiency
gains can still be realized by connecting EXTV
output-derived voltage that has been boosted to greater
OUT
CC
CC
< 8.5V) and from the internal regulator when the
from the output, since the V
CC
CC
CC
CC
Connection
Left Open (or Grounded). This will cause INTV
Connected directly to V
Connected to an External supply. If an external
Connected to an Output-Derived Boost Net-
CC:
CC
CC
LTC3727/LTC3727-1
and INTV
providing it is compatible with the
CC
CC
pin and ensure that EXTV
pin to the INTV
CC
pins. Do not apply greater
CC
CC
OUT
CC
rises above 7.3V, the
CC
remains above 7.0V.
IN
pin directly to V
. This is the normal
CC
and INTV
current resulting
CC
switch than is
pin thereby
CC
CC
CC
CC
17
power
< V
to an
pins.
OUT
3727fc
IN
CC
.
.