MITSUBISHI SEMICONDUCTORS <Standard-Linear>

M62211P/FP

GENERAL PURPOSE MULTI FUNCTION DC-DC CONVERTER

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3) Short Protection Circuit

The Short Protection Circuit used the timer latch system. It is determined by setting the

capacity used for the soft start connected to the DTC terminal.

Fig.3 shows the short protection circuit and the timing chart for various modes.

When the power is turned on, the FB terminal goes high (approx. 2.4V) and the DTC

terminal goes low (goes up slowly from 0V). Thus, approximately 35µA current will flow

when SW1:ON and SW2:OFF. The potential, namely the potential of the FB terminal is in

the amplitude of the triangular wave, SW1 will be OFF and SW2 will be ON and approximately

45µA will flow into the DTC terminal. This discharge current will cause the DTC terminal to

drop from 1.15V.

At this time, if the potential of the FB terminal goes to the control potential before the

potential at the DTC terminal goes lower than 0.45V which is the lower limit value of the

triangular wave and if the potential of the FB terminal is lower than the potential of the DTC

terminal, then the system is activated.

When the output is shorted, the system is either activated or latched depending on

whether the time for the high potential of the FB terminal reaches the potential of the control

state is long or short. (For detail, see [II] and [IV] of the Mode)

There are two ways to go back to operation after the latch to shut off output. Either

method can restart with soft start.

1. Turning ON the Vcc.

2. Make the FB terminal to go to the low potential of 1.25V or less. Then, it is

cancel led.

[Mode Explained]

[ I ] Mode •••••••••••• Activation

This is used when the FB terminal goes down to the control state potential when the DTC

terminal is in up slope. In order for the activation to occur when the DTC terminal is in down

slope, the FB terminal potential must go below the DTC terminal before the DTC terminal

goes to 0.45V.

[ II ] Mode •••••••••••• Output short --> Activation

The system is activated if the FB terminal potential goes below the DTC terminal potential

before the DTC terminal goes to 0.45V. If there is not enough time, the output is turned OFF

(Latched)

[ III ] Mode ••••••••••• ON/OFF Control --> Activation

This mode turns off the output by forcing the DTC terminal to go down. (The system)

returns as in the case of the activation.

[ IV ] Mode ••••••••••• Output Short (Latch)

The output is turned OFF when the FB terminal potential did not go down to the control

state before the DTC terminal went down to 0.45V.

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