LTC3728LEGN Linear Technology, LTC3728LEGN Datasheet - Page 20

• Manufacturer Part Number: LTC3728LEGN
• Description: IC REG SW DUAL 2PH STPDWN 28SSOP
• Manufacturer: Linear Technology
• Series: PolyPhase®r
• Type: Step-Down (Buck)r

Specifications of LTC3728LEGN

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.8 ~ 7 V
• Current - Output: 3A
• Frequency - Switching: 250kHz ~ 550kHz
• Voltage - Input: 4.5 ~ 28 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: -

APPLICATIONS INFORMATION
LTC3728L/LTC3728LX
Panasonic SP , NEC Neocap, Cornell Dubilier ESRE and
Sprague 595D series. Consult manufacturers for other
specifi c recommendations.
INTV
An internal P-channel low dropout regulator produces
5V at the INTV
powers the drivers and internal circuitry within the IC.
The INTV
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 di-
rectly adjacent to the INTV
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 IC to be exceeded.
The system supply current is normally dominated by the
gate charge current. Additional external loading of the
INTV
into account for the power dissipation calculations. The
total INTV
ternal linear regulator or by the EXTV
the voltage applied to the EXTV
of the INTV
regulator. Power dissipation for the IC in this case is high-
est: (V
gate charge current is dependent on operating frequency
as discussed in the Effi ciency Considerations section.
The junction temperature can be estimated by using the
equations given in Note 2 of the Electrical Characteristics.
For example, the IC V
than 67mA from a 24V supply when not using the EXTV
pin as follows:
Use of the EXTV
perature to:
The absolute maximum rating for the INTV
Dissipation should be calculated to also include any added
20
T
T
J
J
CC
CC
= 70°C + (67mA)(24V)(34°C/W) = 125°C
= 70°C + (67mA)(5V)(34°C/W) = 81°C
IN
Regulator
and 3.3V linear regulators also needs to be taken
)(I
CC
CC
INTVCC
CC
pin regulator can supply a peak current of
current can be supplied by either the 5V in-
current is supplied by the internal 5V linear
CC
CC
), and overall effi ciency is lowered. The
pin from the V
input pin reduces the junction tem-
IN
current is thermally limited to less
CC
and PGND IC pins is highly
CC
pin is less than 4.7V, all
IN
supply pin. INTV
CC
input pin. When
CC
pin is 40mA.
CC
CC
current drawn from the internal 3.3V linear regulator.
To prevent maximum junction temperature from being
exceeded, the input supply current must be checked
operating in continuous mode at maximum V
EXTV
The IC contains an internal P-channel MOSFET switch
connected between the EXTV
the voltage applied to EXTV
regulator is turned off and the switch closes, connecting the
EXTV
power. The switch remains closed as long as the voltage
applied to EXTV
MOSFET driver and control power to be derived from the
output during normal operation (4.7V < V
from the internal regulator when the output is out of regu-
lation (start-up, short-circuit). If more current is required
through the EXTV
Schottky diode can be added between the EXTV
INTV
pin and ensure that EXTV
Signifi cant effi ciency gains can be realized by powering
INTV
from the driver and control currents will be scaled by a
factor of (Duty Cycle)/(Effi ciency). For 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
2. EXTV
3. EXTV
INTV
resulting in an effi ciency penalty of up to 10% at high
input voltages.
connection for a 5V regulator and provides the highest
effi ciency.
supply is available in the 5V to 7V range, it may be used
to power EXTV
MOSFET gate drive requirements.
CC
CC
CC
CC
CC
CC
CC
CC
pins. Do not apply greater than 7V to the EXTV
from the output, since the V
Connection
pin to the INTV
to be powered from the internal 5V regulator
Connected Directly to V
Connected to an External Supply. If an external
Left Open (or Grounded). This will cause
CC
CC
:
CC
CC
remains above 4.5V. This allows the
switch than is specifi ed, an external
providing it is compatible with the
CC
CC
pin, thereby supplying internal
CC
< V
rises above 4.7V, the internal
CC
IN
and INTV
.
OUT
CC
IN
pin directly to V
. This is the normal
current resulting
CC
OUT
pins. When
IN
< 7V) and
CC
.
CC
power
3728lxfe
OUT
and
CC
.