34653 datasheet(17/24 Pages) FREESCALE

17 / 24 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

34653

TYPICAL APPLICATIONS

The 34653 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 34653 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 34653: 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 pullup

resistor. Refer to the static and dynamic electrical

characteristics tables on pages 5 through 7 for the various

default values.

Figure 18. Typical Application Diagram with Default

Settings and Minimal External Components

The 34653 can be also programmed for different values of

the Overcurrent Limit and the Charging Current Limit using

external components connected to the device. Figure 19

shows the 34653 with the required external components that

allow access to all programmable features in the device.

Figure 19. Typical Application Diagram with External

Components Necessary to Program the Device

UNDERVOLTAGE AND OVERVOLTAGE

DETECTION

The 34653 monitors 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. Internal comparators connected to an

internal resistor divider between the VPWR and VIN input

pins compare the supply voltages with a reference voltage.

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 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 is above

the undervoltage falling threshold and below the overvoltage

rising threshold, the supply is within operating range and the

Power MOSFET is allowed to turn on and stay on. If the input

voltage falls below its undervoltage falling threshold or rises

above its overvoltage rising threshold, then one of the start-

up conditions (list on page 10) is violated and the Power

MOSFET turns off, the power good signal deactivates, and a

new start-up timer initiates. The undervoltage and

overvoltage detection circuits are equipped with a 1.0 ms

filter to filter out momentary input supply dips.

TIMER

The Timer function on the 34653 provides the time base

used to generate the timing sequences at start-up. The same

timer controls the retry delay when the device experiences

any fault. The Timer function has a default timer value of

VPWR

VIN

ICHG

ILIM

VOUT

33653

GND

-48 V

DC/DC

Converter

Application

Dependent

Enable/Enable

CLOAD

44 k

Ω

PLUG-IN CARD

VPWR

VIN

ICHG

ILIM

VOUT

33653

GND

-48 V

DC/DC

Converter

Application

Dependent

Enable/Enable

CLOAD

44 k

Ω

PLUG-IN CARD

DISABLE

34653 Datasheet(PDF) 17 Page - Freescale Semiconductor, Inc

34653 Datasheet(HTML) 17 Page - Freescale Semiconductor, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL