34652_07 Datasheet, PDF (18/26 Pages) Freescale Semiconductor, Inc – 2.0 A Negative Voltage Hot Swap Controller with Enhanced Programmability

TYPICAL APPLICATIONS
TYPICAL APPLICATIONS
The 34652 resides on the plug-in board (see Figures 18
and 19), allowing the board to be safely inserted or removed
without damaging electrical equipment. The 34652 can be
operated with no external components other than the power
good output signal pull-up resistor if the default mode was
selected for all the programmable features. This is one of the
great advantages of the 34652: it operates with minimal user
interface and minimal external component count and still
offers complete hot swapping functionality with all the
necessary protection features, from undervoltage/
overvoltage detection, to current limiting, to short circuit
protection and power good output signaling. The default
values were chosen to be sufficient for many standard
applications.
Figure 18 is a typical application diagram depicting the
default mode and using the power good output signal pull-up
resistor. Refer to the static and dynamic electrical
characteristics tables on pages 6 through 9 for the various
default values.
GND
PLUG-IN CARD
33652
UV ^VPWR
DISABLE
OV
VIN (4)
PG
PG
VOUT (2)
TIMER ICHG ILIM
44 kΩ
Application
Dependent
Enable/Enable
C_LOAD
DC/DC
Converter
-48 V
Figure 18. Typical Application Diagram with Default
Settings and Minimal External Components
The 34652 can be also programmed for different values of
the Overcurrent Limit, the Charging Current Limit, the Start-
Up and Retry Delay Timer, and the UV / OV detection
thresholds using external components connected to the
device. Figure 19 shows the 34652 with the required external
components that allow access to all programmable features
in the device.
34652
18
GND
PLUG-IN CARD
R₁
33652
UV ^VPWR
PG
R₂
DISABLE
PG
OV
R₃
VIN (4)
VOUT (2)
TIMER ICHG ILIM
44 kΩ
Application
Dependent
Enable/Enable
C_LOAD
DC/DC
Converter
-48 V
Figure 19. Typical Application Diagram with External
Components Necessary to Program the Device
UNDERVOLTAGE AND OVERVOLTAGE
DETECTION
The UV and OV pins are used to monitor the input voltage
to ensure that it is within the operating range and that there
are no overvoltage or undervoltage conditions, and to quickly
turn off the Power MOSFET if there are. The pins are
connected to internal comparators that compare the voltages
at the UV and OV pins with a reference voltage. The UV and
OV pins can be left unconnected for the default threshold
values of their trip point or the user can set the threshold
values externally with a simple voltage divider using resistors
between VPWR and VIN (resistors R₁, R₂, and R₃ in
Figure 19). For the default mode, the 34652 is equipped with
an internal resistor divider that acts the same as the external
one. The typical default values of 37 V for the UV turn-off
threshold (falling threshold) and 78 V for the OV turn-off
threshold (rising threshold) will give a typical operating range
of 38 V to 76 V. This range is suitable for telecom industry
standards.
When the device passes the UVLO threshold, it checks if
there is any external resistor divider connected to the OV and
UV pins. If there is, it determines the value of the UV/OV
thresholds accordingly. If there is not, it defaults to the
internal resistor divider. It then uses the UV/OV detection
circuits to check the input supply levels before turning on the
Power MOSFET during the Start-Up Timer delay and
thereafter. As long as the voltage on the UV pin is above its
falling threshold and the voltage on the OV pin is below its
rising threshold, the supply is within operating range and the
Power MOSFET is allowed to turn on and stay on. If the UV
pin drops below its falling threshold or the OV pin rises above
its rising threshold, then one of the start-up conditions (refer
to page 12 for list) is violated and the Power MOSFET turns
off, the power good signals deactivate, and a new start-up
Analog Integrated Circuit Device Data
Freescale Semiconductor