MC34653EFSLASHR2 datasheet(14/24 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34653

FUNCTIONAL DEVICE OPERATION

PROTECTION AND DIAGNOSIS FEATURES

UNDERVOLTAGE

When the input voltage drops below the undervoltage

falling threshold for more than 1.0 ms, an undervoltage fault

is detected and one of the start-up conditions (list on

page 10) is violated. The 34653 turns off the Power MOSFET

and deactivates the power good output signals, disabling the

load (Point A in Figure 14). The 34653 stays in this state until

the input voltage rises above the undervoltage rising

threshold for more than 1.0 ms, signaling that the supply

voltage is in the normal operation range (Point B in

Figure 14). Then a new start-up sequence initiates as

described on page 10. The undervoltage detection circuit is

also equipped with a 1.0 V hysteresis.

Figure 14. Undervoltage Fault Followed by a

New Start-Up Sequence

Figure 15 shows how the 34653 uses the start-up timer to

make sure that the input voltage is above the undervoltage

falling threshold. The 34653 was in normal operation before

Point A. At Point A an undervoltage fault occurs. Then the

fault is cleared at Point B, and the 34653 initiates a start-up

sequence. Before the end of the start-up timer another

undervoltage fault occurs at Point C, so the 34653 does not

turn on the Power MOSFET. At Point D the fault is cleared

again for the length of the start-up timer and the 34653 turns

on the Power MOSFET and starts the charging process (refer

to Charging Process, pages 10–11).

Figure 15. Start-Up Timer Protection Against

Undervoltage Faults

OVERVOLTAGE

When the input voltage exceeds the overvoltage rising

threshold for more than 1.0 ms, an overvoltage fault is

detected and one of the start-up conditions (list on page 10)

is violated. The 34653 turns off the Power MOSFET and

deactivates the power good output signals, disabling the

load. The 34653 stays in this state until the input voltage falls

below the overvoltage falling threshold for more than 1.0 ms,

signaling that the supply voltage is in the normal operation

range. Then a new start-up sequence initiates as described

on page 10. The overvoltage detection circuit is also

equipped with a 2.0 V hysteresis.

The waveforms for an overvoltage fault are shown in

Figure 16.

Figure 16. Overvoltage Fault

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