Datasheet

LTC3816
20
3816f
applicaTions inForMaTion
Note that the value of R
DCR
must account for its temperature
coefficient, which is approximately 0.39%/°C.
The current limit architecture of the LTC3816 allows short
durations of instantaneous overload. Upon power-up, the
current limit threshold is set to 1×, equal to I
LIMIT
. The
load is limited to I
LIMIT
until the switcher output reaches
its V
BOOT
potential. Beyond this point, during the VID DAC
slewing interval, the I
MAX
sourcing current automatically
switches from 10µA to 20µA and the current limit threshold
increases to 2× to enable the output capacitor voltage to
track the DAC transition. If the controller detects that there
is an overload condition when the DAC is not slewing, the
current limit threshold increases to 2× for a duration of
45µs. If the overload interval is shorter than 45µs, the IC
allows another overcurrent event within the next 630µs,
as shown in Figure 6a. However, if an overload occurs
within the 630µs following the second event, the controller
current limits, as shown in Figure 6b.
If the overload condition persists for more than 45µs,
the LTC3816 allows the 2× current limit to continue for
CURRENT LIMITED
20µA
10µA
I
LOAD
2s
45µs
<45µs
<630µs
1s
I
IMAX
45µs 45µs
<45µs <45µs
3816 F06a
>630µs
Figure 6a. Permissible Overload
CURRENT LIMITED
20µA
10µA
I
LOAD
2s
45µs
<45µs
<630µs <630µs
1s
I
IMAX
45µs
<45µs <45µs
3816 F06b
Figure 6b. Repeated Overload Triggers Current Limit
another cycle. After 90µs, the I
MAX
current returns to 10µA,
and the output load is limited to 1× for the next 630µs as
shown in Figure 6c. Figure 6d shows the condition when
a repetitive overload event triggers current limit.
Figure 6e shows that at any instant, if the load current
is above 1× for more than 90µs, or higher than 2×, the
controller enters current limit. Under this condition, the TG
duty cycle is reduced and the SS capacitor is discharged
CURRENT LIMITED
20µA
10µA
I
LOAD
2s
90µs
1s
I
IMAX
<45µs
3816 F06c
45µs < t < 90µs
45µs
>630µs
Figure 6c. Allowable Longer Overload Condition
CURRENT LIMITED
20µA
10µA
I
LOAD
2s
90µs
1s
I
IMAX
<45µs
3816 F06d
45µs < t < 90µs
<630µs
Figure 6d. Allowable Longer Overload Condition,
Followed by Repeated Overload Triggers Current Limit
CURRENT LIMITED
20µA
10µA
I
LOAD
2s
90µs
>90µs
1s
I
IMAX
45µs
<45µs
3816 F06e
>630µs
Figure 6e. Long Overload or Excessive Loading
Triggers Current Limit Condition