34652 datasheet(18/26 Pages) FREESCALE

18 / 26 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

34652

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.

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.

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

VPWR

VIN

TIMER

ICHG

ILIM

VOUT (2)

33652

(4)

GND

-48 V

DC/DC

Converter

Application

Dependent

Enable/Enable

CLOAD

44 k

Ω

PLUG-IN CARD

DISABLE