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参数资料
| 型号： | LTC4251-1IS6#TRM |
| 厂商： | Linear Technology |
| 文件页数： | 13/24页 |
| 文件大小： | 266K |
| 描述： | IC CTRLR HOTSWAP NEGVOLT SOT23-6 |
| 标准包装： | 500 |
| 类型： | 热交换控制器 |
| 应用： | 通用 |
| 内部开关： | 无 |
| 电源电压： | -36 V ~ -72 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | SOT-23-6 细型，TSOT-23-6 |
| 供应商设备封装： | SOT-23-6 |
| 包装： | 带卷 (TR) |
| 其它名称： | LTC4251-1IS6 LTC4251-1IS6-ND LTC42511IS6 |
13
425112fd
LTC4251/LTC4251-1/
LTC4251-2
For more information www.linear.com/4251
SENSE
The SENSE pin is monitored by the circuit breaker (CB)
comparator, the analog current limit (ACL) amplifier, and
the fast current limit (FCL) comparator. Each of these
three measures the potential of SENSE relative to V
EE
. If
SENSE exceeds 50mV , the CB comparator activates the
230礎 TIMER pull-up. At 100mV , the ACL amplifier servos
the MOSFET current, and at 200mV the FCL compara-
tor abruptly pulls GATE low in an attempt to bring the
MOSFET current under control. If any of these conditions
persists long enough for TIMER to charge C
T
to 4V (see
Equation?2)), the LTC4251/LTC4251-1/LTC4251-2 latch
off and pull GATE low.
If the SENSE pin encounters a voltage greater than 100mV ,
the ACL amplifier will servo GATE downwards in an attempt
to control the MOSFET current. Since GATE overdrives the
MOSFET in normal operation, the ACL amplifier needs time
to discharge GATE to the threshold of the MOSFET . For a
mild overload, the ACL amplifier can control the MOSFET
current, but in the event of a severe overload the current
may overshoot. At SENSE = 200mV , the FCL comparator
takes over, quickly discharging the GATE pin to near V
EE
potential. FCL then releases, and the ACL amplifier takes
over. All the while TIMER is running. The effect of FCL is
to add a nonlinear response to the control loop in favor
of reducing MOSFET current.
Owing to inductive effects in the system, FCL typically
overcorrects the current limit loop, and GATE undershoots.
A zero in the loop (resistor R
C
in series with the gate
capacitor) helps the ACL amplifier recover.
SHORT-CIRCUIT OPERATION
Circuit behavior arising from a load-side low impedance
short is shown in Figure 4. Initially, the current overshoots
the analog current limit level of V
SENSE
= 100mV (Trace 2)
as the GATE pin works to bring V
GS
under control (Trace?).
The overshoot glitches the backplane in the negative
direction, and when the current is reduced to 100mV/R
S
the backplane responds by glitching in the positive
direction.
TIMER commences charging C
T
(Trace 4) while the
analog current limit loop maintains the fault current at
100mV/R
S
, which in this case is 5A (Trace 2). Note that
the backplane voltage (Trace 1) sags under load. When C
T
reaches 4V , GATE turns off, the load current drops to zero
and the backplane rings up to over 100V . The positive peak
is usually limited by avalanche breakdown in the MOSFET ,
and can be further limited by adding a transient voltage
suppressor across the input from 48V to 48RTN, such
as Diodes Inc. SMAT70A.
A low impedance short on one card may influence the
behavior of others sharing the same backplane. The initial
glitch and backplane sag as seen in Figure 4, Trace 1, can
rob charge from output capacitors on adjacent cards. When
the faulty card shuts down, current flows in to refresh the
capacitors. If LTC4251, LTC4251-1 or LTC4251-2s are used
throughout, they respond by limiting the inrush current to
a value of 100mV/R
S
. If C
T
is sized correctly, the capacitors
will recharge long before C
T
times out.
APPLICATIONS INFORMATION
MOSFET SELECTION
The external MOSFET switch must have adequate safe
operating area (SOA) to charge the load capacitance on
start-up and handle short-circuit conditions until TIMER
latchoff. These considerations take precedence over DC
current ratings. A MOSFET with adequate SOA for a given
application can always handle the required current, but
the opposite cannot be said. Consult the manufacturers
MOSFET data sheet for safe operating area and effective
transient thermal impedance curves.
Figure 4. Output Short-Circuit Behavior
(All Waveforms are Referenced to V
EE)
GATE
10V/DIV
SENSE
200mV/DIV
48RTN
50V/DIV
TIMER
5V/DIV
425112 F04
SUPPLY RING
OWING
TO CURRENT
OVERSHOOT
SUPPLY RING
OWING TO
MOSFET
TURN-OFF
ONSET OF OUTPUT
SHORT-CIRCUIT
FAST CURRENT
LIMIT
ANALOG
CURRENT LIMIT
C
TIMER
RAMP
LATCH OFF
TRACE 1
TRACE 2
TRACE 3
TRACE 4
2ms/DIV
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| LTC4251-2CS6#TRM | 功能描述:IC CTRLR HOTSWP NEG VOLT SOT23-6 RoHS:否 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 标准包装:50 系列:- 类型:热交换控制器 应用:-48V 远程电力系统，AdvancedTCA ? 系统，高可用性 内部开关:无 电流限制:可调 电源电压:11.5 V ~ 14.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-MSOP 包装:管件 |
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