IP1842 查看數據表（PDF） - Semelab - > TT Electronics plc

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IP1842

CURRENT MODE REGULATING PULSE WIDTH MODULATORS

Semelab - > TT Electronics plc  

IP1842 SERIES

IP1843 SERIES

APPLICATIONS INFORMATION

Oscillator Waveforms and Maximum Duty Cycle

COMP 1

VFB 2

ISENSE 3

RT /CT 4

8 VREF

7 VCC

6 OUTPUT

5 GROUND

Oscillator timing capacitor CT is charged by VREF

through RT and discharged by an internal current source.

During the discharge time, the internal clock signal

blanks the output to the low state. Selection of RT and

CT therefore determines both oscillator frequency and

maximum duty cycle. Charge and discharge times are

determined by the formulae:

tc » 0.55 RTCT

( ) td » RTCT Rn

.0063 RT – 2.3

.0063 – 4

Resultant frequency

f

=

(tc

1

+

td)

For RT > 5kW,

Resultant frequency

f»

1.8

(RTCT)

Open–Loop Laboratory Test Fixture

COMP 1

N/C 2

VFB 3

N/C 4

ISENSE 5

N/C 6

RT /CT 7

14 VREF

13 N/C

12 VCC

11 VC

10 OUTPUT

9 GROUND

POWER

8 GROUND

High peak current associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should

be connected close to pin 5 in a single point ground. The transistor and 5K potentiometer are used to sample the oscillator wave

form and apply an adjustable ramp to pin 3.

Semelab plc. Telephone +44(0)1455 556565. Fax +44(0)1455 552612.

E-mail: sales@semelab.co.uk Website: http://www.semelab.co.uk

Prelim.3/00

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