PM8801 datasheet(28/37 Pages) STMICROELECTRONICS

Part #	PM8801

Description	High-efficiency, IEEE 802.3at compliant, integrated PoE-PD interface and PWM controller

PDF	37 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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28 / 37 page

PWM controller

PM8801

28/37

DocID018560 Rev 2

PWM controller

5.1

Oscillator

The internal oscillator frequency can be programmed by connecting an external resistor RT

between the FRS and ARTN pins. The relationship between the oscillator frequency FOSC

and the RT resistor is:

The PWM switching frequency is equal to the programmed oscillator frequency.

The useful range for RT is from 25 k to 200 kΩ.

Figure 13. PWM frequency vs. RT

5.2

Delay time control

The delay between the rising edge of GAT2 and GAT1 waveforms can be set by putting a

programming resistor RDT between DT and AGND or VB. The relationship between the

delay time and the RDT resistor is:

osc kHz

()

25000

Ω R

T kΩ

()

--------------------------------------

100

200

300

400

500

600

700

800

900

1000

1100

100

150

200

250

FOSC [kHz]

RT [kΩ]

AM045045v1

del ns

()

1.6R

DT kΩ

()

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