Data Sheet ADP196
Rev. 0 | Page 11 of 12
TIMING
Turn -on delay is defined as the interval between the time that
V
EN
exceeds the rising threshold voltage and when V
OUT
rises to
~10% of its final value. The ADP196 includes circuitry that has
a typical 2 ms turn-on delay and a controlled rise time to limit
the V
IN
inrush current. As shown in Figure 25 and Figure 26,
the turn-on delay is nearly independent of the input voltage.
CH1 20mAΩ CH2 1V M1ms A CH2 1.18V
1
T 10.6%
B
W
CH3 500mV B
W
10704-026
B
W
T
V
OUT
INPUT CURRENT
ENABLE
2
3
Figure 25. Typical Turn-On Time and Inrush Current, V
IN
= 1.8 V,
C
OUT
= 47 μF, 330 Ω Load
CH1 20mAΩ CH2 1V M1ms A CH2 1.18V
1
T 10.6%
B
W
CH3 2V
B
W
10704-027
B
W
T
V
OUT
INPUT CURRENT
ENABLE
2
3
Figure 26. Typical Turn-On Time and Inrush Current, V
IN
= 5 V,
C
OUT
= 47 μF, 330 Ω Load
The rise time is defined as the time it takes the output voltage
to rise from 10% to 90% of V
OUT
reaching its final value. The rise
time is dependent on the rise time of the internal charge pump.
For very large values of output capacitance, the RC time constant
(where C is the load capacitance, C
LOAD
, and R is the RDS
ON
||R
LOAD
)
can become a factor in the rise time of the output voltage. Because
RDS
ON
is much smaller than R
LOAD
, an adequate approximation
for RC is RDS
ON
× C
LOAD
. An input or load capacitor is not required
for the ADP196; however, capacitors can be used to suppress noise
on the board.
The turn-off time is defined as the time it takes for the output
voltage to fall from 90% to 10% of V
OUT
reaching its final value.
The turn-off time is also dependent on the RC time constant
of the output capacitance and load resistance. Figure 27 shows
typical turn-off times with V
IN
= 1.8 V to 5 V, C
OUT
= 47 μF, and
R
LOAD
= 330 Ω.
0
1.0
2.0
3.0
4.0
5.0
6.0
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10
TIME (SEC)
V
OUT
(V)
V
EN
V
IN
= 5.0V
V
IN
= 3.3V
V
IN
= 1.8V
10704-028
Figure 27. Typical Turn-Off Time
CURRENT-LIMIT AND THERMAL OVERLOAD
PROTECTION
The ADP196 is protected against damage due to excessive power
dissipation by current-limit and thermal overload protection
circuits. The ADP196 is designed to limit current when the output
load reaches 4 A (typical). When the output load exceeds 4 A,
the output voltage is reduced to maintain a constant current limit.
Thermal overload protection is included, which limits the junction
temperature to a maximum of 125°C (typical). Under extreme
conditions (that is, high ambient temperature and/or high power
dissipation) when the junction temperature starts to rise above
125°C, the output is turned off, reducing the output current to
zero. When the junction temperature falls below 110°C, the
output is turned on again, and the output current is restored to
its operating value.
Consider the case where a hard short from VOUT to ground
occurs. At first, the ADP196 current limits so that only 4 A is
conducted into the short. If self-heating of the junction is great
enough to cause its temperature to rise above 125°C, thermal
shutdown is activated, turning off the output and reducing the
output current to zero. As the junction temperature cools and
falls below 110°C, the output turns on and conducts 4 A into
the short, again causing the junction temperature to rise above
125°C. This thermal oscillation between 110°C and 125°C causes a
current oscillation between 4 A and 0 mA that continues as long
as the short remains at the output.
Current-limit and thermal overload protections are intended to
protect the device against accidental overload conditions. For
reliable operation, device power dissipation must be externally
limited so that the junction temperature does not exceed 125°C.
