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参数资料
| 型号： | LTC3634IUFD#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 5.5 A DUAL SWITCHING CONTROLLER, 4600 kHz SWITCHING FREQ-MAX, PQCC28 |
| 封装： | 4 X 5 MM, LEAD FREE, PLASTIC, MO-220, QFN-28 |
| 文件页数： | 15/28页 |
| 文件大小： | 359K |
| 代理商： | LTC3634IUFD#TRPBF |
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LTC3634
22
3634f
applicaTions inForMaTion
As an example, consider the case when the LTC3634 is
used to power DDR2 SDRAM and is used in an application
where maximum ambient temperature is 70°C, VIN = 12V,
frequency = 1MHz, VDDQ = 1.8V, VTT = 0.9V, and ILOAD =
2A for both channels.
From the RDS(ON) graphs in the Typical Performance
Characteristics section, the top switch on-resistance is
nominally 140mΩ and the bottom switch on-resistance
is nominally 75mΩ at 70°C ambient. For the VDDQ supply,
the equivalent power MOSFET resistance RSW1 is:
RDS(ON)TOP
1.8V
12V
+RDS(ON)BOT
10.2V
12V
= 84.8m
The same calculation to the VTT supply (0.9V), yields
RSW2 = 79.9mΩ.
From the previous section’s discussion on gate drive, we
estimate the total gate charge current for each regulator to
be 1MHz 2.3nC = 2.3mA, and the total IQ of both chan-
nels is 1.3mA (see the Electrical Characteristics section).
Therefore, the total power dissipated by both regulators is:
PD = IOUT1
(
)2 RSW1
+ IOUT2
( )2 RSW2
+ VIN IGATECHG +IQ
(
)
PD = (2A)2 0.0848 +(2A)2 0.0799
+ 12V 2.3mA 2
(
)+1.3mA
= 0.730W
TheQFN4mm×5mmpackagejunction-to-ambientthermal
resistance,
θJA, is around 43°C/W. Therefore, the junction
temperature of the regulator operating in a 70°C ambient
temperature is approximately:
TJ = 0.730W 43°C/W + 70°C = 101°C
which is below the maximum junction temperature of
125°C. With higher ambient temperatures, a heat sink or
cooling fan should be considered to drop the junction-to-
ambientthermalresistance.Alternatively,theexposedpad
TSSOP package may be a better choice for high power
applications, since it has better thermal properties than
the QFN package.
Remembering that the above junction temperature is ob-
tained from a RDS(ON) at 70°C, we might recalculate the
junction temperature based on a higher RDS(ON) since it
increases with temperature. Redoing the calculation as-
suming that RSW increased 12% at 101°C yields a new
junction temperature of 105°C.
Figure 8 is a temperature derating curve based on the
DC1708 demo board (QFN package). It can be used as
a guideline to estimate the maximum allowable ambient
temperature for given DC load currents in order to avoid
exceeding the maximum operating junction temperature
of 125°C.
Figure 8. Temperature Derating Curve for DC1708 Demo Circuit
Junction Temperature Measurement
The junction-to-ambient thermal resistance will vary de-
pending on the size and amount of heat sinking copper
on the PCB board where the part is mounted, as well as
the amount of air flow on the device. In order to properly
evaluate this thermal resistance, the junction temperature
needstobemeasured.Acleverwaytomeasurethejunction
temperature directly is to use the internal junction diode
on one of the PGOOD pins to measure its diode voltage
change based on ambient temperature change.
FirstremoveanyexternalpassivecomponentonthePGOOD
pin, then pull out 100μA from the PGOOD pin to turn on
its internal junction diode and bias the PGOOD pin to a
negativevoltage.Withnooutputcurrentload,measurethe
PGOOD voltage at an ambient temperature of 25°C, 75°C
and 125°C to establish a slope relationship between the
voltage on PGOOD and ambient temperature. Once this
slopeisestablished,thenthejunctiontemperaturerisecan
0
CHANNEL
1
LOAD
CURRENT
(A)
0.5
1.0
1.5
2.0
3.0
2.5
50
125
3634 F08
0
3.5
25
75
100
MAXIMUM ALLOWABLE AMBIENT
TEMPERATURE (°C)
CH2 LOAD = 0A
CH2 LOAD = 1A
CH2 LOAD = 2A
CH2 LOAD = 3A
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3634MPFE#PBF | 制造商:Linear Technology 功能描述:IC CONV DDR DDR2 DDR3 28TSSOP 制造商:Linear Technology 功能描述:BUCK 15V 3A 500KHZ-4MHZ TS 制造商:Linear Technology 功能描述:BUCK, 15V, 3A, 500KHZ-4MHZ, TSSOP-28 制造商:Linear Technology 功能描述:DP-SWREG/Monolithic, 15V Dual 3A Monolithic Step Down Regulator for DDR Power |
| LTC3634MPFE#TRPBF | 制造商:Linear Technology 功能描述:IC REG 15V 3A STEP DOWN 28-TSSOP 制造商:Linear Technology 功能描述:DC-DC REGULATOR, BUCK, ADJ, TSSOP-28, Primary Input Voltage:15V, No. of Outputs:2, Output Current:3A, No. of Pins:28, Operating Temperature Min:-55C, Operating Temperature Max:150C, MSL:-, Package / Case:28-TSSOP , RoHS Compliant: Yes |
| LTC3634MPUFD#PBF | 制造商:Linear Technology 功能描述:IC CONV DDR DDR2 DDR3 28-QFN 制造商:Linear Technology 功能描述:BUCK 15V 3A 500KHZ-4MHZ QF |
| LTC3637EDHC#PBF | 制造商:Linear Technology 功能描述:IC REG BUCK SYNC ADJ 1A 16DFN |
| LTC3637EMSE#PBF | 制造商:Linear Technology 功能描述:IC REG BUCK SYNC ADJ 1A 16MSOP |
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