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參數(shù)資料
| 型號(hào)： | LTC1695 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | SMBus/I 2 C Fan Speed Controller in SOT-23(SMBus/I 2 C 風(fēng)扇速度控制器（SOT-23封裝）) |
| 中文描述： | 的SMBus /的I 2 C風(fēng)扇調(diào)速器采用SOT - 23（的SMBus /的I 2 C風(fēng)扇速度控制器（采用SOT - 23封裝）） |
| 文件頁數(shù)： | 15/20頁 |
| 文件大小： | 204K |
| 代理商： | LTC1695 |
LTC1695
15
scale (V
FS
) until junction temperature decreases to
approximately 105
°
C. This extended timer period is an
attempt to cool down the system and the LTC1695 by
running the fan at full speed. In most cases, such elevated
ambient temperatures require the fan to run at full speed
anyway. The remaining LTC1695’s functionality remains
unchanged.
Thermal Shutdown, Overcurrent
The LTC1695 shuts down the P-channel linear regulator if
die temperature exceeds 155
°
C typically. The thermal
shutdown circuitry employs about 30
°
C of hysteresis. As
previously mentioned, the LTC1695 sets bit 6 (THE) in the
SMBus data byte register HIGH during thermal shutdown
conditions. During a fault condition, the LTC1695’s SMBus
logic continues to operate so that the SMBus host can read
back the fault status data.
During an overload or short-circuit fault condition, the
LTC1695’s current-limit detector sets bit 7 (OCF) in the
SMBus data byte register HIGH and actively limits output
current to 390mA typically. This protects the LTC1695’s
P-channel pass transistor. Under dead short conditions
with V
OUT
= 0V, the LTC1695 also clamps the output
current. However, the increased power dissipation
(5V 390mA = 1.95W) eventually forces the LTC1695 into
thermal shutdown. The LTC1695 will then thermally oscil-
late until the fault condition is removed.
During recovery from thermal shutdown (typically 125
°
C),
the LTC1695 automatically activates the boost start timer,
programming the fan voltage to full scale for 250ms
(T
BST_ST
), before switching to the user programmed out-
put voltage value. This again eliminates fan start-up prob-
lems if the thermal shutdown fault occurred while the fan
was previously operating at an output voltage below the
fan’s starting voltage. In addition, as discussed, the boost
start timer will keep V
OUT
at V
FS
for an extended time
period beyond T
BST_ST
until the LTC1695’s junction tem-
perature drops below 105
°
C.
The LTC1695’s protection features protect itself, the fan,
and more importantly alerts the SMBus host to any system
thermal management fault conditions.
For further information, refer to the Junction Temperature
Increase (above ambient temperature) vs I
LOAD
graph in
the Typical Performance Characteristics section. This
graph provides a fast and simple junction temperature
estimation with various V
OUT
(DAC code) and I
LOAD
combinations for a typical application.
Boost Start Timer
In general, a 5V brushless DC fan starts at a voltage value
higher than the voltage at which it stalls. This behavior is
directly attributed to the force necessary to overcome the
back EMF of the fan. For example, one fan measured
started at 3.5V but operated until its terminal voltage fell
below 2.1V. Therefore, users must ensure start-up in the
fan before programming the fan voltage to a value lower
than the starting voltage. Monitoring the fan’s DC current
for a stalled condition does not work due to the fan’s
resistive nature. Fans can sink load current even though
they are not rotating. Other approaches include detecting
absence of the fan’s commutation ripple current and
tachometers. In general, these approaches are more com-
plex, require more circuitry, add cost and have to be
customized for the specific fan used.
The LTC1695 contains a programmable boost start timer
offering three flexible solutions to the user:
1.) Enable the boost start timer bit (D6 in the DAC com-
mand code). Each time a new output voltage is pro-
grammed, the timer forces V
OUT
to full scale (4.922V
nominal with V
CC
= 5V) for 250ms before assuming the
programmed output voltage value. This ensures fan start
up even if the programmed output voltage is below the
fan’s start threshold.
2.) Users may also choose to use a software timer routine
inside the host controller to power the DC fan, at full scale,
for a programmed time period before programming V
OUT
to a lower desired DAC output voltage code.
3.) Users may choose a tachometer fan that feedbacks its
speed to the SMBus host. If fan stall conditions are
detected, the SMBus host re-programs the LTC1695.
Beyond a typical 125
°
C LTC1695 junction temperature,
the boost start timer (if activated) maintains V
OUT
at full
APPLICATIO
S I
N
FOR
ATIO
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| LTC1695CS5#TR | 功能描述:IC CTRLR FAN SPD SMBUS SOT23-5 RoHS:否 類別:集成電路 (IC) >> PMIC - 電機(jī)和風(fēng)扇控制器，驅(qū)動(dòng)器 系列:- 產(chǎn)品變化通告:ATA683(3,4)PLQW Obsolescence 09/Aug/2012 標(biāo)準(zhǔn)包裝:1 系列:- 應(yīng)用:DC 電機(jī)控制器，無刷（BLDC），3 相 評(píng)估套件:可供 輸出數(shù):1 電流 - 輸出:100mA 電壓 - 負(fù)載:5.25 V ~ 20 V 電源電壓:5.25 V ~ 20 V 工作溫度:-40°C ~ 150°C 安裝類型:表面貼裝 封裝/外殼:48-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:48-VQFN（7x7） 包裝:剪切帶 (CT) 其它名稱:ATA6833-PLQWCT |
| LTC1695CS5#TRM | 功能描述:IC CTRLR FAN SPD SMBUS SOT23-5 RoHS:否 類別:集成電路 (IC) >> PMIC - 電機(jī)和風(fēng)扇控制器，驅(qū)動(dòng)器 系列:- 產(chǎn)品變化通告:ATA683(3,4)PLQW Obsolescence 09/Aug/2012 標(biāo)準(zhǔn)包裝:1 系列:- 應(yīng)用:DC 電機(jī)控制器，無刷（BLDC），3 相 評(píng)估套件:可供 輸出數(shù):1 電流 - 輸出:100mA 電壓 - 負(fù)載:5.25 V ~ 20 V 電源電壓:5.25 V ~ 20 V 工作溫度:-40°C ~ 150°C 安裝類型:表面貼裝 封裝/外殼:48-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:48-VQFN（7x7） 包裝:剪切帶 (CT) 其它名稱:ATA6833-PLQWCT |
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