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参数资料
| 型号： | LTC3727AIG-1#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3 A SWITCHING CONTROLLER, 580 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封装： | 5.30 MM, LEAD FREE, PLASTIC, SSOP-28 |
| 文件页数： | 9/32页 |
| 文件大小： | 328K |
| 代理商： | LTC3727AIG-1#TRPBF |
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LTC3727A-1
17
3727a1fa
INTVCC Regulator
An internal P-channel low dropout regulator produces 7.5V
at the INTVCC pin from the VIN supply pin. INTVCC powers
the drivers and internal circuitry within the LTC3727A-1.
The INTVCC pin regulator can supply a peak 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 di-
rectly adjacent to the INTVCC and PGND IC pins 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
maximum junction temperature rating for the LTC3727A-1
to be exceeded. The system supply current is normally
dominated by the gate charge current. Additional external
loading of the INTVCC and 3.3V linear regulators also
needs to be taken into account for the power dissipation
calculations. The total INTVCC current can be supplied by
either the 7.5V internal linear regulator or by the EXTVCC
input pin. When the voltage applied to the EXTVCC pin is
less than 7.3V, all of the INTVCC current is supplied by
the internal 7.5V linear regulator. Power dissipation for
the IC in this case is highest: (VIN)(IINTVCC), and overall
efciency is lowered. The gate charge current is dependent
on operating frequency as discussed in the Efciency
Considerations section. The junction temperature can be
estimated by using the equations given in Note 2 of the
Electrical Characteristics. For example, the LTC3727A-1
VIN current is limited to less than 24mA from a 24V supply
when not using the EXTVCC pin as follows:
TJ = 70°C + (24mA)(24V)(95°C/W) = 125°C
Use of the EXTVCC input pin reduces the junction tem-
perature to:
TJ = 70°C + (24mA)(7.5V)(95°C/W) = 87°C
APPLICATIONS INFORMATION
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
exceeded, the input supply current must be checked
operating in continuous mode at maximum VIN.
EXTVCC Connection
The LTC3727A-1 contains an internal P-channel MOSFET
switch connected between the EXTVCC and INTVCC pins.
When the voltage applied to EXTVCC rises above 7.3V,
the internal regulator is turned off and the switch closes,
connecting the EXTVCC pin to the INTVCC pin thereby sup-
plying internal power. The switch remains closed as long
as the voltage applied to EXTVCC remains above 7.0V. This
allows the MOSFET driver and control power to be derived
from the output during normal operation (7.2V < VOUT <
8.5V) and from the internal regulator when the output is
out of regulation (start-up, short-circuit). If more current
is required through the EXTVCC switch than is specied,
an external Schottky diode can be added between the
EXTVCC and INTVCC pins. Do not apply greater than 8.5V
to the EXTVCC pin and ensure that EXTVCC < VIN.
Signicant efciency gains can be realized by powering
INTVCC from the output, since the VIN current resulting
from the driver and control currents will be scaled by a
factor of (Duty Cycle)/(Efciency). For 7.5V regulators
this supply means connecting the EXTVCC pin directly to
VOUT. However, for 3.3V and other lower voltage regula-
tors, additional circuitry is required to derive INTVCC power
from the output.
The following list summarizes the four possible connec-
tions for EXTVCC:
1. EXTVCC Left Open (or Grounded). This will cause
INTVCC to be powered from the internal 7.5V regulator
resulting in an efciency penalty of up to 10% at high
input voltages.
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