max5059auit Maxim Integrated Products, Inc., max5059auit Datasheet - Page 21

• Manufacturer Part Number: max5059auit
• Description: Parallelable, Secondary-side Synchronous Rectifier Driver And Feedback-generator Controller Ics
• Manufacturer: Maxim Integrated Products, Inc.

Figure 16. Idealized (with Ideal Power Stage and Optocoupler)
Frequency Response (G PS (s)) from Noninverting Input of the
Error Amplifier to the Output of the Power Supply for the
Typical Application Circuit of Figure 18
Figure 17. Overall Open-Loop Response of the Current-Share
Loop
Figure 16 shows the idealized small-signal response of
the Typical Application Circuit from the noninverting
input of the error amplifier to the output. This response
shows that the unity-gain crossover frequency of the
current-share loop can easily be placed between 10Hz
and 100Hz, while at the same time avoiding interaction
with the main voltage-control loop.
For frequencies below 100Hz, G
(using the DC gain value for G
Parallelable Secondary-Side Synchronous Rectifier
-20
-40
-60
-80
-10
-15
-20
80
60
40
20
20
15
10
-5
0
5
0
1
1
Driver and Feedback-Generator Controller ICs
GAIN
POWER-STAGE GAIN/PHASE
______________________________________________________________________________________
10
10
PHASE
FREQUENCY (Hz)
FREQUENCY (Hz)
100
100
PS
GAIN
(s)):
T
1k
(s) can be written as
1k
PHASE
10k
10k
180
135
90
45
0
-45
-90
-135
-180
90
45
0
-45
-90
Equating |G
The current-sharing loop is compensated with a capac-
itor from COMPS to GND. This results in a dominant
pole that forces the loop gain of the current-share loop
to cross 0dB with a single pole (20dB/decade) rolloff.
When R
Example:
R
V
f
R
The resulting overall open-loop response of the current-
share control loop is shown in Figure 17.
Figure 18 shows a complete design of an isolated syn-
chronously rectified power supply with a +36V to +75V
telecom input voltage range. This design uses the
MAX5051 as the primary-side controller and the
MAX5058 as the secondary-side synchronous rectifier
driver. Figures 19 though 24 show some of the perfor-
mance aspects of this power-supply design. This
power supply can sustain a continuous short circuit at
its output terminals. This circuit is available as a com-
pletely built and tested evaluation kit (MAX5058EVKIT).
CS
OUT
S
LOAD
= 2mΩ
= 10Hz
G s
C
= 3.3V
T
COMPS
= 0.22Ω
C
LOAD
C
( )
COMPS
COMPS
=
×
T
20
| = 1 and solving for C
Isolated 48V Input Power Supply
>> R
V
V
=
≅
×
IREF
OUT
Applications Information
0 11
(
=
s C
=
36 61
.
×
S
(
(
(
36 61
, the above can be simplified further.
.
500
36 61
×
μ
F
COMPS
R
.
.
μ
S
μ
F Hz V
f
CS
S
μ
+
μ
×
)
(
R
F Hz V
F Hz V
R
10
f
S
×
CS
LOAD
×
×
Hz
×
(
R
/
(
×
S
1 15
)
)
/
/
R
.
×
+
×
LOAD
(
R
)
)
COMPS
(
0 22
0 002
×
μ
×
LOAD
.
.
A V
R
R
S
S
/
Ω
×
×
Ω
)
)
)
V
V
×
yields:
)
OUT
OUT
R
×
IREF
(
3 3
.
V
)
21