Datasheet

TPS60120, TPS60121, TPS60122, TPS60123, TPS60124, TPS60125
REGULATED 200-mA HIGH EFFICIENCY CHARGE PUMP
DC/DC CONVERTERS
SLVS257B – NOVEMBER 1999 – REVISED AUGUST 2000
6
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
low-battery detector (TPS60120, TPS60122, TPS60124)
The internal low-battery comparator trips at 1.21 V ±5% when the voltage on LBI ramps down. The battery
voltage at which the comparator initiates a low battery warning at the LBO output can easily be programmed
with a resistive divider as shown in Figure 1. The sum of resistors R1 and R2 is recommended to be in the 100-kΩ
to 1-MΩ range.
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
(TRIP)
1.21 V 1
R1
R2
_
+
+
–
V
REF
V
BAT
IN
R1
LBI
R2
LBO
R3
V
O
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 1M
V
LBI
V
Bat
R1 1M 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 R1/kΩ R2/kΩ V
BAT (MIN)
/V V
BAT(MAX)
/V
1.8 357 732 1.700 –5.66% 1.902 5.67%
1.9 365 634 1.799 –5.32% 2.016 6.11%
2.0 412 634 1.883 –5.86% 2.112 5.6%
2.1 432 590 1.975 –5.95% 2.219 5.67%
2.2 442 536 2.080 –5.45% 2.338 6.27%
Using ±1% accurate resistors, the total accuracy of the trip voltage is about ±6%, considering the ±4% accuracy
the integrated voltage reference adds and considering that not every calculated resistor value is available.