参数资料
型号: LTC4251-1IS6#TRM
厂商: Linear Technology
文件页数: 7/24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:
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
7
425112fd
LTC4251/LTC4251-1/
LTC4251-2
For more information www.linear.com/4251
PIN FUNCTIONS
SENSE (Pin 1): Circuit Breaker/Current Limit SENSE Pin. 
Load current is monitored by sense resistor R
S
 connected
between SENSE and V
EE
, and controlled in three steps. If
SENSE exceeds V
CB
(50mV), the circuit breaker comparator
activates a 230礎 TIMER pin pull-up current. The LTC4251/
LTC4251-1/LTC4251-2 latch off when C
T
 charges to 4V . If
SENSE exceeds V
ACL
 (100mV), the analog current limit
amplifier pulls GATE down and regulates the MOSFET
current at V
ACL
/R
S
. In the event of a catastrophic short-
circuit, SENSE may overshoot 100mV . If SENSE reaches
V
FCL
 (200mV), the fast current limit comparator pulls
GATE low with a strong pull-down. To disable the circuit
breaker and current limit functions, connect SENSE to V
EE
.
Kelvin-sense connections between the sense resistor and
the V
EE
 and SENSE pins are strongly recommended, see
Figure 6.
V
EE
 (Pin 2): Negative Supply Voltage Input. Connect this 
pin to the negative side of the power supply.
V
IN
 (Pin 3): Positive Supply Input. Connect this pin to the 
positive side of the supply through a dropping resistor.
A shunt regulator typically clamps V
IN
 at 13V . An internal
undervoltage lockout (UVLO) circuit holds GATE low until
the V
IN
 pin is greater than V
LKO
 (9.2V), overriding UV/OV . If
UV is high, OV is low and V
IN
 comes out of UVLO, TIMER
starts an initial timing cycle before initiating a GATE ramp
up. If V
IN
 drops below approximately 8.2V , GATE pulls low
immediately.
TIMER (Pin 4): Timer Input. TIMER is used to generate 
a delay at start-up, and to delay shutdown in the event of
an output overload. TIMER starts an initial timing cycle
when the following conditions are met: UV is high, OV is
low, V
IN
 clears UVLO, TIMER pin is low, GATE is lower than
V
GATEL
 and V
SENSE
  V
EE
 < V
CB
. A pull-up current of 5.8礎
then charges C
T
, generating a time delay. If C
T
 charges to
V
TMRH
 (4V) the timing cycle terminates, TIMER quickly
pulls low and GATE is activated.
If SENSE exceeds 50mV while GATE is high, a 230礎
pull-up current charges C
T
. If SENSE drops below 50mV
before TIMER reaches 4V , a 5.8礎 pull-down current
slowly discharges C
T
. In the event that C
T
  eventually
integrates up to the 4V V
TMRH
 threshold, TIMER latches
high with a 5.8礎 pull-up source and GATE quickly pulls
low. The LTC4251/LTC4251-1/LTC4251-2 fault latches may
be cleared by either pulling TIMER low with an external
device, or by pulling UV/OV below V
UVLO
.
UV/OV (Pin 5): Undervoltage/Overvoltage Input. This dual 
function pin detects undervoltage as well as overvoltage.
The high threshold at the UV comparator is set at V
UVHI
 
with V
UVHST
 hysteresis. The high threshold at the OV
comparator is set at V
OVHI
 with V
OVHST
 hysteresis. If UV/
OV < V
UVLO
 or UV/OV > V
OVHI
, GATE pulls low. If UV/OV
> V
UVHI
 and UV/OV < V
OVLO
, the LTC4251/LTC4251-1/
LTC4251-2 attempt to start-up. The internal UVLO at V
IN
 
always overrides UV/OV . A low at UV resets an internal fault
latch. A high at OV pulls GATE low but does not reset the
fault latch. A 1nF to 10nF capacitor at UV/OV eliminates
transients and switching noise from affecting the UV/OV
thresholds and prevents glitches at the GATE pin.
GATE (Pin 6): N-Channel  MOSFET  Gate  Drive  Output. 
This pin is pulled high by a 58礎 current source. GATE is
pulled low by invalid conditions at V
IN
 (UVLO), UV/OV , or
the fault latch. GATE is actively servoed to control fault
current as measured at SENSE. A compensation capacitor
at GATE stabilizes this loop. A comparator monitors GATE
to ensure that it is low before allowing an initial timing
cycle, GATE ramp up after an overvoltage event, or restart
after a current limit fault.
 
UV/OV refers to the UV pin for the LTC4251-2. The OV comparator in the LTC4251-2 is disabled. All
references in the text to overvoltage, OV, V
OVHI
 and V
OVLO
 do not apply to the LTC4251-2.
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