MAX5058EUI+T Datasheet MAX5058EUI+T, MAX5059AUI+T, MAX5058AUI+ | P16-P18

Figure 8 shows a typical configuration with output volt-

ages high enough (V

OUT

> 2.5V) to allow a typical

optocoupler to be fully biased. In this case, there are

two feedback paths—one though the error amplifier

and one through the output-connected optocoupler.

This second feedback path must be considered when

compensating the overall feedback loop.

Figure 9 shows a typical configuration with an optocou-

pler for output voltages lower than 2.5V. In this case,

the direct connection of the optocoupler to the output is

not possible. There is only one feedback path and the

error-amplifier feedback network must be designed

accordingly.

Figure 10 shows the simplified block diagram for the

error amplifier.

Voltage Margining

The margining inputs MRGU (margin up) and MRGD

(margin down) control two internal MOSFETs with open-

drain outputs at RMGU and RMGD, respectively. When

margining is used, connect two pullup resistors from

RMGU and RMGD to I

REF

. A logic-high voltage at

MRGU causes QMU (see Figure 1) to open, increasing

the equivalent resistance at I

REF

and the reference volt-

age (V

IREF

). The error-amplifier inverting input, INV,

tracks I

REF

and forces the primary-side controller to

increase the output voltage. MRGD has the opposite

effect. When a logic high is applied to MRGD, QMD

turns on, decreasing the equivalent resistance at I

REF

and effectively reducing V

IREF

. This causes INV to track

and force the primary-side controller to reduce the out-

put voltage.

The margining inputs MRGU and MRGD are internally

pulled to GND with 40kΩ resistors. When margining is

not used, the inputs can be left floating or connected to

GND to make V

IREF

= 50µA × R12.

Calculation Procedure for Output-Voltage Setting

Resistors and Margining

Use the following step-by-step procedure to calculate

the output-voltage setting and margining resistors (see

the Typical Application Circuit):

MAX5058/MAX5059

Parallelable Secondary-Side Synchronous Rectifier

Driver and Feedback-Generator Controller ICs

16 ______________________________________________________________________________________

COMPV

INV

REF

E/A

REF

50μA

R12

OUT

> 2.5V

C28

R12

R19

C27

Figure 8. Optocoupler Connection for V

OUT

> 2.5V

COMPV

INV

REF

E/A

REF

50μA

R12

0.5V < V

OUT

< 2.5V

C28

Rff

R19

C27

REG

(PIN 23)

Figure 9. Optocoupler Connection for V

OUT

< 2.5V

COMPV

INV

REF

Figure 10. Simplified Error-Amplifier Diagram

MAX5058/MAX5059

Parallelable Secondary-Side Synchronous Rectifier

Driver and Feedback-Generator Controller ICs

______________________________________________________________________________________ 17

1) Select a parallel equivalent resistance R

value to

produce the nominal reference voltage. For exam-

ple, R

= 35.4kΩ gives you V

IREF

= 1.77V.

2) Select the margin-up percentage value:

ΔU = 5%

3) Calculate R

= 743.4kΩ. Calculated

Select the nearest 0.1% value.

= 741kΩ. Selected

4) Calculate R

= 37.05kΩ. Calculated

Select the nearest 0.1% value.

= 37kΩ. Selected

5) Select the margin-down percentage value:

ΔD = 5%

6) Recalculate R

with the selected values:

= 35.24kΩ.

7) Calculate R

= 361.186kΩ. Calculated

Select the nearest 0.1% value:

= 361kΩ. Selected

8) Calculate the reference voltage with the selected

chosen values:

IREF

= 50µA ✕ R

from step 6.

IREF

= 1.762V.

RDR

100

100 100

××

×+

()

%%Δ -

12 32

100

eq32

100

=×

% Δ

Figure 11. Remote-Sense Amplifier Connection for 0.5V ≤ V

OUT

≤ 2.5V

OUT

VSP

VSN

VSO

COMPV

INV

REF

E/A

REF

50μA

R12

C28

OUT

= (50μA) x R12

FOR: 0.5V ≤ V

OUT

≤ 2.5V

RSA

9) Select a value for R

and calculate R

for V

OUT

3.3V:

= 19.1kΩ

= 21.882kΩ.

Select the nearest 1% value.

= 21.8kΩ.

When margining is not used, substitute R

for R

in step 8 and go to step 9.

Remote-Sense Amplifier

Use the remote-sense amplifier (RSA in Figure 1) to

directly sense the voltage across the load, compensat-

ing for voltage drops in PC board tracks or load con-

nection wires. The remote-sense amplifier is a

unity-gain amplifier with sufficient bandwidth to not

interfere with the normal operation of the voltage-con-

trol loop. Direct sensing of the output voltage is possi-

ble if the output voltage is between 0.5V to 2.5V. Figure

11 shows this configuration. Figure 12 shows the use of

the remote-sense amplifier with a voltage-divider. The

remote-sense amplifier has an input bias current of

100µA. The impedance of R1 and R2 must be kept low

in this configuration to avoid excessive errors in the out-

put-voltage set point.

Current Sharing

When multiple power modules are providing power to

the same load, the load current must be shared equally

to provide the best reliability and thermal distribution.

The MAX5058/MAX5059 contain circuitry that enable

current sharing among paralleled power supplies with-

out requiring an explicit controlling master circuit.

Current sharing is accomplished by connecting togeth-

er the current-share bus pins (SFP and SFN) of all par-

alleled power supplies (see Figure 13), thus creating a

current-force/share bus. The voltage level on this differ-

ential bus is proportional to the output current of the

power supply that has the highest current compared to

the other supplies. The number of power supplies that

can be paralleled with this method is limited only by

practical considerations.

IREF

OUT IREF

MAX5058/MAX5059

Parallelable Secondary-Side Synchronous Rectifier

Driver and Feedback-Generator Controller ICs

18 ______________________________________________________________________________________

Figure 12. Remote-Sense Amplifier Connection for V

OUT

> 2.5V (or any Other Arbitrary Voltage)

OUT

VSP

VSN

VSO

RSA

COMPV

OUT

= 1 +

IREF

= (

50μA

)

✕ R12

INV

REF

E/A

REF

50μA

R12

C28

( )

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P25

MAX5058EUI+T

Mfr. #:

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Manufacturer:

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Description:

Gate Drivers Secondary Side Synch Rectifier Driver

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