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

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-k

Ω

to 1-M

Ω range.

LBO is an open drain output. An external pullup resistor to OUT, in the 100-k

Ω 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

1

) R1

R2

_

+

+

–

VREF

VBAT

IN

R1

LBI

R2

LBO

R3

VO

Figure 1. Programming of the Low-Battery Comparator Trip Voltage

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%),

VBAT/V

R1/k

Ω

R2/k

Ω

VBAT (MIN)/V

VBAT(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.