Texas Instruments TPS3801, Application Report

Page: 16 / 28

Manual Reset
12 SLVA075
100 ns
V
MR
VDD
0.7
×
VDD
0.3
×
VDD
0 V t
Figure 14. Minimum Conditions for Triggering a Reset at Manual Reset Input
4.4 Saving Current While Using the Manual Reset Function
4.4.1 Current Flow Off the Manual Reset Input
Figure 15 illustrates the internal structure of the manual reset input. It shows
the internal pullup resistor of 30 k
Ω
, which causes a steady current flow, if
V
MR
≠
V
DD
. If it is important to keep the current consumption as low as possible,
the following two points are important to considerate:
•
In normal operation V
MR
should be equal to V
DD
. Thereby a steady current
flow can be avoided.
•
If a reset should be triggered with a low pulse at manual reset, it should be
a short pulse.
Reset
Logic
30 k
Ω
VDD
MR
VMR
Voltage
Source
TPS3801
IMR
Figure 15. Internal Realization of the Manual Reset Circuit
The current out of the manual reset terminal depends on the difference between
V
DD
and VMR and can be easily calculated with equation 2.
I
MR
+
V
DD
*
V
MR
30 k
W
4.4.2 Lateral Current From V
DD
to GND
There is another possibility to reduce power consumption while using the manual
reset. During a transition at MR from high-to-low or low-to-high, there is a lateral
current of more than 300
µ
A at a voltage of 2.5 V. Power consumption is important
in a battery powered system and a steep edge in both directions helps to minimize
power consumption. The following Figure 16 shows the lateral current in
dependence of the voltage at manual reset input.
(2)