XC9235 TOREX SEMICONDUCTOR LTD., XC9235 Datasheet - Page 10

• Manufacturer Part Number: XC9235
• Description: Xc9235 600ma Synchronous Step-down Dc/dc Converters
• Manufacturer: TOREX SEMICONDUCTOR LTD.

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■OPERATIONAL DESCRIPTION (Continued)
<Short-Circuit Protection>
The short-circuit protection circuit monitors the internal R1 and R2 divider voltage from the V
the block diagram shown in the previous page). In case where output is accidentally shorted to the Ground and when
the FB point voltage decreases less than half of the reference voltage (Vref) and a current more than the I
the driver transistor, the short-circuit protection quickly operates to turn off and to latch the driver transistor. In latch
mode, the operation can be resumed by either turning the IC off and on via the CE/MODE pin, or by restoring power
supply to the V
When sharp load transient happens, a voltage drop at the V
short circuit protection may operate in the voltage higher than 1/2 V
<U.V.L.O. Circuit>
When the V
pulse output caused by unstable operation of the internal circuitry. When the V
switching operation takes place. By releasing the U.V.L.O. function, the IC performs the soft start function to initiate
output startup operation. The soft start function operates even when the V
U.V.L.O. operating voltage. The U.V.L.O. circuit does not cause a complete shutdown of the IC, but causes pulse output
to be suspended; therefore, the internal circuitry remains in operation.
<PFM Switch Current>
In PFM control operation, until coil current reaches to a specified level (I
case, time that the P-ch MOSFET is kept on (TON) can be given by the following formula.
TON= L
<Maximum I
In PFM control operation, the maximum duty ratio (MAXI
the duty increases (e.g. the condition that the step-down ratio is small), it’s possible for P-ch MOSFET to be turned off even
when coil current doesn’t reach to I
XC9235/XC9236/XC9237
×
I
I Lx
PFM
Lx
IPFM①
IN
PFM
IN
pin voltage becomes 1.4V or lower, the P-channel output driver transistor is forced OFF to prevent false
(V
Limit>
pin.
IN
−
Ton
V
OUT
)
→I
PFM
PFM
①
.
→I
IPFM
0mA
PFM
Series
②
PFM
OUT
) is set to 200% (TYP.). Therefore, under the condition that
is propagated to the FB point through C
IPFM②
I Lx
Lx
OUT
M axum um IPFM Current
voltage.
PFM
), the IC keeps the P-ch MOSFET on. In this
IN
FOSC
pin voltage falls momentarily below the
IN
pin voltage becomes 1.8V or higher,
OUT
pin (refer to FB point in
IPFM
0mA
FB
, as a result,
LIM
flows to