Texas Instruments TPS6100 EVM Series, Руководство пользователя

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Low-Battery Function LBI and LBO
4-3
Setup of the EVM
4.2 Low-Battery Function LBI and LBO
The low battery feature is typically used to supervise the battery voltage and
to indicate when the voltage goes below an adjustable threshold voltage. The
threshold voltage can be adjusted by an external resistive divider connected
to the low-battery input (LBI) as shown in Figure 4–2. It can be calculated by
using equation 1.
V
threshold
R
2
R
1
1 V
REF
909 k
1
M
1 0.5 V 0.955 V
(1)
On the EVM, the threshold voltage is adjusted to about 0.96 V. If the battery
voltage goes below 0.96 V, the LBO open-drain output is pulled down to
ground. Otherwise, it is in a high-impedance state and the voltage is pulled up
via the external resistor R6 to V
O
. R1 is a 1-M
Ω
resistor, so that the current
through R1 is about 50 times higher than the typical current into the LBI pin of
10 nA. Therefore, the LBI input current can be neglected in the calculations.
Figure 4–2. Resistive Divider at LBI
TPS6100x
LBI LBO
R2
909 k
Ω
R1
1 M
Ω
R6
470 k
Ω
V
LBO
Note:
Voltage drops can be found on the input line although there are two input ca-
pacitors. These spikes can be the reason for triggering the LBO earlier than
expected, since the input voltage decreases the adjusted threshold voltage
for short periods of time. Be aware of this.