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参数资料
| 型号： | LTC3827IUH#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3 A DUAL SWITCHING CONTROLLER, 580 kHz SWITCHING FREQ-MAX, PQCC32 |
| 封装： | 5 X 5 MM, PLASTIC, MO-220WHHD, QFN-32 |
| 文件页数： | 14/36页 |
| 文件大小： | 451K |
| 代理商： | LTC3827IUH#TR |
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LTC3827
21
3827ff
APPLICATIONS INFORMATION
gate charge current, may be supplied by either the 5.25V
VIN LDO or the 7.5V EXTVCC LDO. When the voltage on
the EXTVCC pin is less than 4.7V, the VIN LDO is enabled.
Power dissipation for the IC in this case is highest and is
equal to VIN INTVCC. 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 LTC3827 INTVCC
current is limited to less than 24mA from a 24V supply
when in the G package and not using the EXTVCC supply:
TJ = 70°C + (24mA)(24V)(95°C/W) = 125°C
To prevent the maximum junction temperature from being
exceeded, the input supply current must be checked while
operating in continuous conduction mode (PLLIN/MODE
= INTVCC) at maximum VIN.
When the voltage applied to EXTVCC rises above 4.7V, the
VIN LDO is turned off and the EXTVCC LDO is enabled. The
EXTVCC LDO remains on as long as the voltage applied to
EXTVCC remains above 4.5V. The EXTVCC LDO attempts
to regulate the INTVCC voltage to 7.5V, so while EXTVCC
is less than 7.5V, the LDO is in dropout and the INTVCC
voltage is approximately equal to EXTVCC. When EXTVCC
is greater than 7.5V up to an absolute maximum of 10V,
INTVCC is regulated to 7.5V.
Using the EXTVCC LDO allows the MOSFET driver and
control power to be derived from one of the LTC3827’s
switching regulator outputs (4.7V ≤ VOUT ≤ 10V) during
normal operation and from the VIN LDO when the output
is out of regulation (e.g., start-up, short-circuit). If more
current is required through the EXTVCC LDO than is spec-
ied, an external Schottky diode can be added between the
EXTVCC and INTVCC pins. Do not apply more than 10V to
the EXTVCC pin and make sure than EXTVCC ≤ VIN.
Signicant efciency and thermal gains can be realized
by powering INTVCC from the output, since the VIN cur-
rent resulting from the driver and control currents will be
scaled by a factor of (Duty Cycle)/(Switcher Efciency). For
5V to 10V regulator outputs, this means connecting the
EXTVCC pin directly to VOUT. Tying the EXTVCC pin to a 5V
supply reduces the junction temperature in the previous
example from 125°C to:
TJ = 70°C + (24mA)(5V)(95°C/W) = 81°C
However, for 3.3V and other low voltage outputs, addi-
tional 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 5.25V regulator
resulting in an efciency penalty of up to 10% at high
input voltages.
2. EXTVCC Connected directly to VOUT. This is the normal
connection for a 5V to 10V regulator and provides the
highest efciency.
3. EXTVCC Connected to an External supply. If an external
supply is available in the 5V to 10V range, it may be
used to power EXTVCC providing it is compatible with
the MOSFET gate drive requirements.
4. EXTVCCConnectedtoanOutput-DerivedBoostNetwork.
For 3.3V and other low voltage regulators, efciency
gains can still be realized by connecting EXTVCC to an
output-derived voltage that has been boosted to greater
than 4.7V. This can be done with the capacitive charge
pump shown in Figure 8.
Figure 8. Capacitive Charge Pump for EXTVCC
EXTVCC
VIN
TG1
SW
BG1
PGND
LTC3827
RSENSE
VOUT
VN2222LL
+
COUT
3827 F08
N-CH
+
CIN
1μF
VIN
L1
BAT85
0.22μF
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