MITSUBISHI SEMICONDUCTORS <Standard Linear ICs>
M62212P/FP/GP
GENERAL PURPOSE DC-DC CONVERTER
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. 2.3V) and the DTC
terminal goes low (goes up slowly from 0V). Thus, approximately 45µA 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
50µA 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 1.86V 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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MITSUBISHI [ MITSUBISHI ELECTRIC SEMICONDUCTOR ]
