LTC1998 Просмотр технического описания (PDF) - Linear Technology

Номер в каталоге

Компоненты Описание

производитель

LTC1998

2.5µA, 1% Accurate SOT-23 Comparator and Voltage Reference for Battery Monitoring

Linear Technology 

LTC1998

APPLICATIONS INFORMATION

The calculation of the resistor values R1, R2 and R3 is

quite straightforward and similar to the procedure outlined

in the previous paragraph.

Choose a value for the sum of R1 + R2 + R3 as well as the

values for low battery threshold and hysteresis.

Solve for resistor R1:

R1= (R1+R2 +R3)

⎛

⎝⎜

5V

VTH2

⎞

– 1⎠⎟

Solve for the sum of

⎛

(R1+R2) = (R1+R2 +R3) ⎝⎜

5V

VBATT.Th

⎞

– 1⎠⎟

then solve for R2 and R3.

Example: A system needs to detect a low battery

voltage of 3V (VBATT.Th = 3V) with 250mV hysteresis

(VTH2 = 3.25V). Set the value of the resistor divider

(R1 + R2 + R3) = 1M.

R1 = 539k, R1 + R2 = 667k, R2 = 128k, R3 = 333k.

Choose the closest 1% values, that is 536k, 332k, 127k.

Figure 4 graphically shows the function of the LTC1998 as

described above.

VERSATILE OUTPUT DRIVER

VLOGIC, BATTLO (Pins 5,6)

The LTC1998 uses a CMOS push-pull output stage to drive

the low battery output signal. This output pin (BATTLO)

has a separate supply pin, (VLOGIC) that can be used to

provide an output voltage rail matching the VDD logic of

microprocessors. The VLOGIC pin may be tied to a volt-

age lower than the voltage at the BATT pin. The VLOGIC

pin may also be tied to a voltage higher than VBATT via a

series resistor greater than 10k. The output will then act

as an open-drain device.

In a given application, if it is possible for BATTLO to be

shorted to GND or a supply, a series resistor should be

added to limit the short-circuit current to 5mA.

3.25V

PROGRAMMED

HYSTERESIS

THRESHOLD

PROGRAMMED

LOW BATT

THRESHOLD

2.50V

VLOGIC

PROGRAMMABLE

THRESHOLD RANGE

BATTERY

VOLTAGE

HYSTERESIS

BATTERY VOLTAGE

RECOVERS UNDER

REDUCED LOAD

BATTLO

1998 F04

Figure 4. LTC1998 Function Plot

1998fa

10

Share Link: