Rainbow Electronics MAX5971B - Manual (Page 38)

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MAX5971B
Single-Port, 40W, IEEE 802.3af/at,
PSE Controller with I 2 C
mode. When DET_BY is set to 1 however, the MAX5971B
can power the port without doing the detection routine.
AC_TH[2:0] (R23h[2:0]) allows direct programming of
the AC disconnect threshold. The threshold is defined
as a current since the comparator verifies that the peak
current pulses sensed at the DET input exceeds a preset
threshold. The current threshold is defined as follows:
I AC_TH = 85.28FA + 10.64FA x N AC_TH
where N AC_TH is the decimal value of AC_TH[2:0]. The
default N AC_TH is 4 (AC_TH[2:0] = 100) which corre-
sponds to a default I AC_TH of ~128FA.
PWM Register (R24h)
The PWM register (R24h, Table 33) is used to program
the PWM duty cycle. On a power-up or after a reset
condition, this register is set to a default value of 0x00h.
PWM_TH[1:0] (R24h[5:4]) is used to set the PWM duty
cycle. The default PWM_TH[1:0] value of 00 corresponds
to a 6.25% duty cycle, while the maximum PWM_TH[1:0]
value of 11 corresponds to a 25% duty cycle (see Table 34).
Table 33. PWM Register
Table 34. PWM Duty-Cycle Settings
PWM_TH[1:0] DUTY CYCLE (%)
00 6.25
01 12.5
10 18.75
11 25.0
ADDRESS = 24h
DESCRIPTION
SYMBOL BIT NO. R/W
Reserved 7 — Reserved
Reserved 6 — Reserved
PWM_TH
5 R/W PWM_TH[1]
4 R/W PWM_TH[0]
Reserved
3 R/W
Internally connected. For a write command, always write a zero to this bit.
2 R/W
1 R/W
0 R/W