參數(shù)資料
型號(hào): LTC3856EFE#PBF
廠商: LINEAR TECHNOLOGY CORP
元件分類(lèi): 穩(wěn)壓器
英文描述: SWITCHING CONTROLLER, PDSO38
封裝: 4.4 MM, LEAD FREE, PLASTIC, TSSOP-38
文件頁(yè)數(shù): 20/40頁(yè)
文件大小: 2222K
代理商: LTC3856EFE#PBF
LTC3856
3856f
TIME
(11a) Coincident Tracking
VOUT1
VOUT2
OUTPUT
VOLTAGE
3856 F11a
VOUT1
VOUT2
TIME
3856 F11b
(11b) Ratiometric Tracking
OUTPUT
VOLTAGE
Figure 11. Two Different Modes of Output Voltage Tracking
R3
R1
R4
R2
R3
VOUT2
R4
(12a) Coincident Tracking Set-Up
TO
VFB1
PIN
TO
TK/SS2
PIN
TO
VFB2
PIN
VOUT1
R1
R2
R3
VOUT2
R4
3856 F12
(12b) Ratiometric Tracking Set-Up
TO
VFB1
PIN
TO
TK/SS2
PIN
TO
VFB2
PIN
VOUT1
Figure 12. Set-Up and Coincident and Ratiometric Tracking
applicaTions inForMaTion
is needed to supply the high transient currents required
by the MOSFET gate drivers and to prevent interaction
between the channels.
High input voltage applications in which large MOSFETs
are being driven at high frequencies may cause the maxi-
mum junction temperature rating for the LTC3856 to be
exceeded. The INTVCC current, which is dominated by the
gate charge current, may be supplied by either the 5V LDO
or EXTVCC. When the voltage on the EXTVCC pin is less
than 4.7V, the LDO is enabled. Power dissipation for the
IC in this case is highest and is equal to VIN IINTVCC. The
gate charge current is dependent on operating frequency
as discussed in the Efficiency Considerations section.
The junction temperature can be estimated by using the
equations given in Note 3 of the Electrical Characteristics
table. For example, the LTC3856 INTVCC current is limited
to less than 42mA from a 38V supply in the UH package
and not using the EXTVCC supply:
TJ = 70°C + (42mA)(38V)(34°C/W) = 125°C
To prevent the maximum junction temperature from be-
ing exceeded, the input supply current must be checked
while operating in continuous conduction mode (MODE
= SGND) at maximum VIN. When the voltage applied to
EXTVCC rises above 4.7V, the INTVCC LDO is turned off
and the EXTVCC is connected to the INTVCC. The EXTVCC
remainsonaslongasthevoltageappliedtoEXTVCCremains
above 4.5V. Using the EXTVCC allows the MOSFET driver
and control power to be derived from one of switching
regulator outputs during normal operation and from the
INTVCC when the output is out of regulation (e.g., start-up,
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