RC4153 Ver la hoja de datos (PDF) - Fairchild Semiconductor

Número de pieza

componentes Descripción

Fabricante

RC4153

Voltage-to-Frequency Converter

Fairchild Semiconductor 

PRODUCT SPECIFICATION

RC4153

I OUT

Q10

(B)

Q7 Q8

II

1.0 mA

Q11 Q12

D3

Q6

Gnd

Q2

Q1

D2

Q3

D1

Q4 Q5

Trigger

C

D

VTH

Q13 Q14

CO

Ramp Generator

IT

Comparator

Figure 9. One-Shot (Detail)

R-S Latch

-VS

4153-12

The switched current source is shown as a block diagram in

Figure 10 and detailed in Figure 11. The summing node

(+ input of the op amp) is held at 0V by the amplifier feed-

back, causing VREF to be applied across R60. This current

(VREF/R60), minus the small amplifier bias current, flows

through Q35. Q35 develops a VBE dependent on that current.

This VBE is developed across Q36. Since Q35 and Q36 are

equal in area, the currents are equal. The mirrored current is

switched by the one-shot output.

The detail schematic shows the amplifier and load (Q21

through Q34), the mirror transistors (Q35, Q36) and the dif-

ferential switching transistors (Q7, Q8). The amplifier uses a

complementary paraphase input composed of Q21 through

Q26 with a current mirror formed by Q27 through Q30,

which converts from differential to single-ended output.

Level-shift diodes Q32 and Q34 and emitter follower Q31

bootstrap the emitters of the mirror devices Q29 and Q30 to

increase gain and lower input offsets, which would otherwise

be caused by unbalanced collector voltages on Q23 and Q26.

VREF

+7.3V

R60

A Switched

Current

Source

Output

B

From

One Shot

Q35

Q36

-VS

4153-13

Figure 10. Switched Current Source Block Diagram

12

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