Micrel
MIC2589/MIC2595
caused by common mode transients. Such is the
case when an EMI filter is utilized to prevent DC-DC
converter switching noise from being injected back
onto the power supply. The circuit of Figure 11 shows
how to configure an optoisolator driven by the
/PWRGD signal of the MIC2589 controller.
Power-Good Signals Driving Optoisolators
The PWRGDx signals can be used to drive
optoisolators or LEDs. The use of an optoisolator is
sometimes needed to protect I/O signals (e.g.,
/PWRGD, RESET, ENABLE) of both the controller
and downstream DC-DC converter(s) from damage
R7
43k
R6
43k
R5
43k
OPTO#1
OPTO#2
OPTO#3
1
6
1
6
1
6
MOC207-M
MOC207-M
MOC207-M
2
5
2
5
2
5
-48V RTN
(Long Pin)
-48V RTN
MIC2589-2BM
*D1
SMAT70A
1
2
3
4
5
6
7
14
/PWRGD1
VDD
/PWRGD3
/PWRGD2
DRAIN
IN+
OUT+
+5VOUT
R1
689k
1%
R2
11.8k
1%
C4
100µF
CTIMER
0.068µF
C3
0.1µF
ON/OFF*
13
12
11
10
9
PGTIMER
UV
-48V RTN
(Short Pin)
IN–
IN+
OUT–
+5V RTN
OV
CFILTER
2.2µF
C1
0.47µF
OUT+
+2.5VOUT
CFILTER
CNLD
VEE
GATE
C6
100µF
C5
0.1µF
ON/OFF*
R3
12.4k
1%
SENSE
N/C
CNLD
0.068µF
IN–
OUT–
+2.5V RTN
*C2
8
0.1µF
R4
10
IN+
OUT+
+1.8VOUT
C8
100µF
C7
0.1µF
ON/OFF*
IN– OUT–
-48V RTN
(Long Pin)
+1.8V RTN
RSENSE
M1
0.01
5%
SUM110N10-09
Nominal Undervoltage and Overvoltage Thresholds:
VUV = 36.5V
VOV = 71.2V
*Optional components (See Funtional Description and Applications Information for more details)
#An external pull-up resistor for the power-good signal is necessary for DC-DC convertors (and all other load modules) not equipped with an
internal pull-up impedance
Figure 11. Optoisolators Driven by /PWRGD Signals
27
M9999-120505
(408) 955-1690
December 2005
MICREL [ MICREL SEMICONDUCTOR ]
