TPS60204_15 Datasheet, PDF (6/21 Pages) Texas Instruments – REGULATED 3.3-V 100-MA LOW-RIPPLE CHARGE PUMP LOW POWER DC/DC CONVERTERS

TPS60204, TPS60205
REGULATED 3.3ĆV, 100ĆmA LOWĆRIPPLE CHARGE PUMP
LOW POWER DC/DC CONVERTERS
SLVS354A − FEBRUARY 2001 − REVISED SEPTEMBER 2001
detailed description (continued)
low-battery detector (TPS60204)
The low-battery comparator trips at 1.18 V ±4% when the voltage on pin LBI ramps down. The voltage V_(TRIP)
at which the low-battery warning is issued can be adjusted with a resistive divider as shown in Figure 2. The
sum of resistors R1 and R2 is recommended to be in the 100-kΩ to 1-MΩ range. When choosing R1 and R2,
be aware of the input leakage current into the LBI pin.
LBO is an open drain output. An external pullup resistor to OUT, or any other voltage rail in the appropriate range,
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. The low-battery detector is disabled when the device is
switched off.
VO
R3
LBO
IN
_
LBI
+
+
VREF _−
VBAT
R1
R2
ǒ Ǔ V_(TRIP) + 1.18 V
1
)
R1
R2
Figure 2. Programming of the Low-Battery Comparator Trip Voltage
A 100-nF ceramic 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.
Formulas to calculate the resistive divider for low-battery detection, with V_LBI = 1.13 V to 1.23 V and the sum
of resistors R1 and R2 equal 1 MΩ:
R2 + 1 MW
VLBI
VBat
(1)
R1 + 1 MW * R2
(2)
Formulas to calculate the minimum and maximum battery voltage:
VBat(min) + VLBI(min)
R1(min) ) R2(max)
R2(max)
(3)
VBat(max) + VLBI(max)
R1(max) ) R2(min)
R2(min)
(4)
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