Datasheet

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SLVS258A − NOVEMBER 1999 − REVISED DECEMBER 1999
6
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
low-battery detector (TPS60130 and TPS60132) (continued)
LBO is an open drain output. An external pullup resistor to OUT, in the 100-kΩ to 1-MΩ range is recommended.
During start-up, the LBO output signal is invalid for the first 500 µs. LBO is high impedance when the device
is disabled.
If the low-battery comparator function is not used, connect LBI to ground and leave LBO unconnected.
_
+
+
−
V
REF
V
BAT
IN
R1
LBI
R2
LBO
V
TRIP
+ 1.21 V
ǒ
1 )
R1
R2
Ǔ
V
OUT
R3
Figure 1. Programming of the Low-Battery Comparator Trip Voltage
Formulas to calculate the resistive divider for low battery detection, with V
LBI
= 1.15 V − 1.27 V:
R2 + 1MW
V
LBI
V
BAT
R1 + 1MW * R2
Formulas to calculate the minimum and maximum battery voltage that triggers the low battery detector:
V
BAT(min)
+ V
LBI(min)
R1
(min)
) R2
(max)
R2
(max)
V
BAT(max)
+ V
LBI(max)
R1
(max)
) R2
(min)
R2
(min)
Table 1. Recommended Values for the Resistive Divider from the E96 Series (±1%),
V
LBI
= 1.15 V − 1.27 V
V
BAT
/V R
1
/kΩ R
2
/kΩ V
BAT(MIN)
/V V
BAT(MAX)
/V
2.7 562 453 2.548 −5.61% 2.877 6.57%
2.8 576 442 2.619 −6.47% 2.958 5.66%
2.9 590 422 2.726 −6.00% 3.081 6.26%
3.0 590 402 2.804 −6.53% 3.172 5.72%
3.1 604 383 2.928 −5.56% 3.313 6.88%
3.2 619 374 3.016 −5.76% 3.414 6.70%
3.3 649 374 3.106 −5.88% 3.518 6.62%
A 100 nF bypass capacitor should be connected in parallel to R2 if large line transients are expected. These
voltage drops can inadvertently trigger the low-battery comparator and produce a wrong low-battery warning
signal at the LBO pin.