VOUT
5usec(typ)
Ifthecurrentlimitprotectioncircuit
doesnotdetectduring5usec,itshifts
tonomaloperationmode.
NomalOperation
Mode
Current
Limit4A
Current
Limit1.5A
CoilCurrent
0A
0V
PABIAS1
0V
CurrentLimit
1.5A detectionMode
5usec(typ)
1.5A detectcontinuously
1.5A detectionstart
(c)1.5 A Detection
Short-Circuit Protection
SLVS708B – NOVEMBER 2006 – REVISED APRIL 2007
Figure 74. Current Limit Protection - View
The DC/DC converter incorporates short-circuit protection (SCP) in addition to current-limit protection (CLP)
circuitry. The current-limit protection circuit applies to the peak current detection of the coil, while the short-circuit
protection circuit detects the level of the output voltage.
Figure 75 (a) shows the operation of short-circuit
protection. The output voltage of VOUT decreases when current-limit operates, limiting the current through the
coil. Short-circuit protection occurs when 80% or less of the target output voltage value is detected while in the
normal operation mode, thereby shifting from normal operation mode to SCP monitor mode. An internal
oscillator provides the timing for a 0.5 msec (typ) delay before shifting to SCP-monitor mode. The two protection
circuits (current-limit protection and short-circuit protection) operate in this manner, shifting to SCP mode when
the output voltage of VOUT does not exceed the target value for 0.5 msec (typ), even if passing, and the VOUT
pin is adjusted to 0V for 8 msec (typ). The analog circuit of the DC/DC converter is enabled for the 8-msec (typ)
period, after which the DC/DC converter powers up from soft-start mode. If the output voltage of VOUT exceeds
80% of the target value after soft-start mode ends, it operates in normal operation mode. The short-circuit
protection circuit continuously monitors the output voltage value of VOUT. It transitions from soft-start mode to
normal-operation mode once, after power up, as shown in
Figure 75 (b), and then if the output voltage of VOUT
does not achieve 80% of the target output voltage, it again shifts to SCP-monitor mode. It shifts to SCP mode
when the output voltage of VOUT does not exceed the target value for 0.5 msec (typ), even if passing, and the
VOUT pin is adjusted to 0V for 8 msec (typ). The DC/DC converter keeps repeating this intermittent operation as
long as there is no setting change from the host.
Figure 75 (c) shows the image chart for intermittent operation.
Note that the detection time is counted by an internal oscillator, which generates the switching frequency (fs) of
the DC/DC converter.
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