PM8803 STMicroelectronics, PM8803 Datasheet - Page 25

• Manufacturer Part Number: PM8803
• Description: High efficiency integrated IEEE 802.3at PoE-PD interface and PWM controller type 2 PSE indicator, plus support for forward active clamp topology
• Manufacturer: STMicroelectronics

PM8803
5
5.1
5.2
PWM controller
Oscillator
The internal oscillator frequency can be programmed by connecting an external resistor R
between the FRS and ARTN pins. The relationship between the oscillator frequency F
and the R
The PWM switching frequency is equal to the programmed oscillator frequency.
The useful range for R
Figure 11. PWM frequency vs. R
Delay time control
The delay between the rising edge of GAT2 and GAT1 waveforms can be set by putting a
programming resistor R
delay time and the R
t
del
(
F
ns
F
OSC
osc
)
[kHz]
=
(
T
kHz
1.6R
resistor is:
1000
1100
)
900
800
700
600
500
400
300
200
100
DT
=
0
(
------------------------------------- -
3kΩ
kOhm
0
DT
25000
+
T
20
DT
resistor is:
R
is between 20 k to 200 kOhm
)
T
(
between DT and AGND or VB. The relationship between the
kΩ
40
Doc ID 018559 Rev 1
)
60
T
80
100
R
T
[kOhm]
120
140
160
180
200
220
PWM controller
240
AM045101v1
OSC
25/34
T