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| 型号： | MC34653EFR2 |
| 厂商： | Freescale Semiconductor |
| 文件页数： | 18/24页 |
| 文件大小： | 1649K |
| 描述： | IC CTRLR HOT SWAP NEG V 8-SOIC |
| 标准包装： | 2,500 |
| 类型： | 热交换开关 |
| 应用： | 通用 |
| 内部开关： | 是 |
| 电流限制： | 1A |
| 电源电压： | 36 V ~ 80 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SOICN |
| 包装： | 带卷 (TR) |
Analog Integrated Circuit Device Data
18
Freescale Semiconductor
34653
TYPICAL APPLICATIONS
rchived by Freescale Semiconductor, Inc., 2008
200 ms. During start-up and if any fault occurred, this timer
value is used when initiating a start-up sequence.
POWER GOOD OUTPUT SIGNALS
The power good pins PG and PG
are output pins that are
used to directly enable a power module load. The device has
active high and active low power good output signals.
Choosing which power good active signal depends on the
Enable signal requirement of the load. This feature allows the
34653 to adapt to different applications and a wide variety of
loads.
The power good output signal is active if the Power
MOSFET is fully enhanced and the device is in normal
operation. The signal goes active after a typical 20 ms delay.
The signal deactivates if one of the following occurs:
" Power is turned off.
" The device is disabled for more than 1.0 ms.
" The device exceeded its thermal shutdown threshold for
more than 12 約.
" The device is in overvoltage or undervoltage mode for
more than 1.0 ms.
" Load current exceeded the overcurrent limit for more than
3.0 ms.
When the power good output signal becomes inactive, it
disables the load, protecting it from any faults or damage.
These loads are usually DC/ DC converters, depicted in
Figure 19
, page 17
. An LED can also be connected to PG
to
indicate that the power is good.
The PG and PG
pins are referenced to VIN and require a
pullup resistor connected to VPWR
(Figures 18
and 19
,
page 17
).
DISABLING AND ENABLING THE 34653
The Disable control input (DISABLE) provides two
functions:
" External enable /disable control.
" Manual resetting of the device and the retry counter after
a fault has occurred.
Using the DISABLE pin, a user can enable /disable the
34653 device, which facilitates easy access to connect the
load to or disconnect it from the main power rail.
When power is first applied, the DISABLE pin must be
inactive in order for the 34653 to initiate a start-up sequence.
If the DISABLE pin is active, the device makes no further
steps until the pin is inactive. At any point during the start-up
and thereafter during normal operation, if the DISABLE pin is
activated, then the retry counter resets, the Power MOSFET
turns off and the power good output signals deactivate. The
DISABLE circuit is equipped with a 1.0 ms filter to filter out
any glitches or transients on the DISABLE input and prevent
the Power MOSFET from turning off prematurely.
The DISABLE pin is referenced to VPWR . If left open or
connected to VPWR, meaning the voltage at the DISABLE
pin is between V
PWR
+ 1.2 V and V
PWR
- 1.2 V, it is inactive
and the device is enabled. If a positive voltage (1.8 V above
V
PWR
) or a negative voltage (1.8 V below V
PWR
) is applied to
DISABLE, it is active and the device is disabled.
CHARGING CURRENT LIMIT
When the device passes the UVLO threshold, it checks if
there is any external resistor or external capacitor connected
to the ICHG
pin. If there is, then it determines the value of the
charging current limit value and the charging current limit rise
time accordingly. If there is not, it uses the default charging
current limit value of 100 mA and rise time of 1.0 ms.
Note Users are allowed to connect an external capacitor
to ICHG pin only if an external resistor is also connected.
During the external components check, a capacitor produces
an impulse of current and an external resistor will be
detected, even it the external resistor is absent.
When the Power MOSFET is turned on, the current limit is
set gradually from 0 A to I
CHG
. This current charges up the
load capacitor relatively slowly. When the load capacitor is
fully charged, the Power MOSFET reaches its full
enhancement, which triggers the current limit to change from
I
CHG
to I
LIM
and the load current to decrease. The power good
output signals activate after a 20 ms delay, which in turn
enables the load. The 34653 is now in normal operation
mode and the retry counter resets.
The low charging current value of I
CHG
is intended to limit
the temperature increase during the load capacitor charging
process, and the gradual rise to I
CHG
is to prevent transient
dips in the input voltage due to sharp increases in the limit
current. This prevents the input voltage from drooping due to
current steps acting on the input line inductance, and that in
turn prevents a premature activation of the UV detection
circuit.
Choosing the External Resistor R
ICHG
Value
The user can change the value of the charging current limit
by adding a resistor (R
ICHG
) between the ICHG and VIN pins,
as shown in Figure 19
, page 17
. The charging current value
ranges between 50 mA and 500 mA, with a default value of
100 mA. Table 6
lists examples of R
ICHG
for different values
of I
CHG
and Figure 20
shows a plot of R
ICHG
versus I
CHG
. It is
recommended that the closest 1% standard resistor value to
the actual value be chosen.
Note Accuracy requirements are application dependent.
To calculate the value of the R
ICHG
resistor we use the
following equations:
I
CHG
(A)
= [ R
ICHG
(k? + 1.4 k / 335
R
ICHG
(k? = 335
*
I
CHG
(A)
- 1.4 k?/DIV>
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