参数资料
| 型号： | LTC3819EG#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 17/32页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR STEP DOWN 36-SSOP |
| 标准包装： | 2,000 |
| 应用： | 控制器，Sun 服务器 |
| 输入电压： | 4 V ~ 36 V |
| 输出数： | 1 |
| 输出电压： | 1.03 V ~ 1.41 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 36-SSOP（0.209"，5.30mm 宽） |
| 供应商设备封装： | 36-SSOP |
| 包装： | 带卷 (TR) |
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LTC3819
APPLICATIO S I FOR ATIO
INTV CC Regulator
An internal P-channel low dropout regulator produces 5V
at the INTV CC pin from the V IN supply pin. The INTV CC
regulator powers the drivers and internal circuitry of the
LTC3819. The INTV CC pin regulator can supply up to 50mA
peak and must be bypassed to power ground with a
minimum of 4.7 μ F tantalum or electrolytic capacitor. An
additional 1 μ F ceramic capacitor placed very close to the
IC is recommended due to the extremely high instanta-
neous currents required by the MOSFET gate drivers.
High input voltage applications in which large MOSFETs
are being driven at high frequencies may cause the maxi-
mum junction temperature rating for the LTC3819 to be
exceeded. The supply current is dominated by the gate
charge supply current, in addition to the current drawn
from the differential amplifier output. The gate charge is
dependent on operating frequency as discussed in the
Efficiency Considerations section. The supply current can
either be supplied by the internal 5V regulator or via the
EXTV CC pin. When the voltage applied to the EXTV CC pin
islessthan4.7V,alloftheINTV CC loadcurrentissupplied
by the internal 5V linear regulator. Power dissipation for
the IC is higher in this case by (I IN )(V IN – INTV CC ) and
efficiency is lowered. The junction temperature can be
estimated by using the equations given in Note 1 of the
Electrical Characteristics. For example, the LTC3819 V IN
current is limited to less than 24mA from a 24V supply:
T J = 70 ° C + (24mA)(24V)(85 ° C/W) = 119 ° C
Use of the EXTV CC pin reduces the junction temperature to:
T J = 70 ° C + (24mA)(5V)(85 ° C/W) = 80.2 ° C
The input supply current should be measured while the
controller is operating in continuous mode at maximum
V IN and the power dissipation calculated in order to
prevent the maximum junction temperature from being
exceeded.
EXTV CC Connection
When the voltage applied to EXTV CC rises above 4.7V, the
internal regulator is turned off and an internal switch
closes, connecting the EXTV CC pin to the INTV CC pin
thereby supplying internal and MOSFET gate driving power
to the IC. The switch remains closed as long as the voltage
applied to EXTV CC remains above 4.5V. This allows the
MOSFET driver and control power to be derived from a
separate 5V supply during normal operation (4.7V <
V EXTVCC < 7V) and from the internal regulator when the
external 5V supply is not available. Do not apply greater
than 7V to the EXTV CC pin and ensure that EXTV CC < V IN +
0.3V when using the application circuits shown. If an
external voltage source is applied to the EXTV CC pin when
the V IN supply is not present, a diode can be placed in
series with the LTC3819’s V IN pin and a Schottky diode
between the EXTV CC and the V IN pin, to prevent current
from backfeeding V IN .
Topside MOSFET Driver Supply (C B ,D B ) (Refer to
Functional Diagram)
External bootstrap capacitors C B1 and C B2 connected to
the BOOST1 and BOOST2 pins supply the gate drive
voltages for the topside MOSFETs. Capacitor C B in the
Functional Diagram is charged though diode D B from
INTV CC when the SW pin is low. When the topside MOSFET
turns on, the driver places the C B voltage across the gate-
source of the desired MOSFET. This enhances the MOSFET
and turns on the topside switch. The switch node voltage,
SW, rises to V IN and the BOOST pin rises to V IN + V INTVCC .
The value of the boost capacitor C B needs to be 30 to 100
times that of the total input capacitance of the topside
MOSFET(s). The reverse breakdown of D B must be greater
than V IN(MAX).
The final arbiter when defining the best gate drive ampli-
tude level will be the input supply current. If a change is
made that decreases input current, the efficiency has
improved. If the input current does not change then the
efficiency has not changed either.
The LTC3819 contains an internal P-channel MOSFET
switch connected between the EXTV CC and INTV CC pins.
3819f
17
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