TSM921 datasheet(16/20 Pages) SILABS

16 / 20 page

TSM921-TSM924

Page 16

TSM921/24 Rev. 1.0

Figure 6. Bar-Graph Level Gauge

In this example, a 1M

Ω, 1% standard value

resistor is selected for R3.

Using the equations below, verify all resistor

values selected:

VOTH = (VREF + VHYS) x

R1 + R2 + R3

= 5.474V

VOTH = (VREF - VHYS) x

R1 + R2 + R3

(R1+R2)

= 4.484V

Where the hysteresis voltage is given by:

VHYS = VREF x

Bar-Graph Level Gauge

A simple four-stage level detector is shown in

Figure 6 using the TSM924. Due to its high output

source capability, the TSM921 is perfect for driving

LEDs. When all of the LEDs are on, the threshold

voltage is set by resistors R1 and R2 where VIN =(R1

+ R2)/R1 volts. All other threshold voltages are

scaled down accordingly by ¾, ½, and ¼ the

threshold voltage. The current through the LEDs is

limited by the output resistors.

Level Shifter

Figure 7 provides a simple way to shift from bipolar

±5V inputs to TTL signals by using the TSM924. To

protect the comparator inputs, 10k

Ω resistors are

placed in series and do not have an effect on the

performance of the circuit.

Figure 7. Level Shifter: ±5V Input into CMOS output

TSM921 Datasheet(PDF) 16 Page - Silicon Laboratories