LTC3728L LINER [Linear Technology], LTC3728L Datasheet - Page 17

• Manufacturer Part Number: LTC3728L
• Description: Dual, 550kHz, 2-Phase Synchronous Regulators
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
NEC Neocap, Cornell Dubilier ESRE and Sprague 595D
series. Consult manufacturers for other specific recom-
mendations.
INTV
An internal P-channel low dropout regulator produces 5V
at the INTV
the drivers and internal circuitry within the IC. The INTV
pin regulator can supply a peak current of 50mA and must
be bypassed to ground with a minimum of 4.7 F tanta-
lum, 10 F special polymer, or low ESR type electrolytic
capacitor. A 1 F ceramic capacitor placed directly adja-
cent to the INTV
mended. 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 ex-
ceeded. The system supply current is normally dominated
by the gate charge current. Additional external loading of
the INTV
taken into account for the power dissipation calculations.
The total INTV
internal 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
highest: (V
The gate charge current is dependent on operating fre-
quency as discussed in the Efficiency 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
mally limited to less than 67mA from a 24V supply when
not using the EXTV
Use of the EXTV
ture to:
The absolute maximum rating for the INTV
Dissipation should be calculated to also include any added
T
T
J
J
CC
= 70 C + (67mA)(24V)(34 C/W) = 125 C
= 70 C + (67mA)(5V)(34 C/W) = 81 C
Regulator
CC
CC
IN
CC
and 3.3V linear regulators also needs to be
)(I
pin from the V
current is supplied by the internal 5V linear
CC
INTVCC
CC
CC
current can be supplied by either the 5V
input pin reduces the junction tempera-
CC
U
and PGND IC pins is highly recom-
), and overall efficiency is lowered.
pin as follows:
U
IN
supply pin. INTV
CC
pin is less than 4.7V, all
W
CC
IN
input pin. When
current is ther-
CC
Pin is 40mA.
U
CC
powers
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
nal regulator is turned off and the switch closes, connect-
ing the EXTV
internal power. The switch remains closed as long as the
voltage applied to EXTV
allows the MOSFET driver and control power to be derived
from the output during normal operation (4.7V < V
7V) and from the internal regulator when the 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 7V 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 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 5V regulator resulting in
an efficiency penalty of up to 10% at high input voltages.
2. EXTV
connection for a 5V regulator and provides the highest
efficiency.
3. EXTV
supply is available in the 5V to 7V range, it may be used to
power EXTV
gate drive requirements.
CC
CC
from the output, since the V
CC
CC
CC
Connection
Left Open (or Grounded). This will cause INTV
Connected directly to V
Connected to an External supply. If an external
CC
CC
LTC3728L/LTC3728LX
CC:
providing it is compatible with the MOSFET
CC
pin to the INTV
and INTV
CC
pin and ensure that EXTV
CC
CC
CC
remains above 4.5V. This
CC
rises above 4.7V, the inter-
pins. Do not apply greater
CC
and INTV
OUT
pin thereby supplying
CC
IN
pin directly to V
. This is the normal
CC
current resulting
switch than is
CC
pins. When
IN
CC
.
CC
17
power
< V
OUT
3728lxfa
OUT
IN
CC
<
.
.