PoE synchronous flyback, IEEE802.3at compliant, 5V - 4A PD ... · GLOOP bandwidth > 3 kHz GLOOP phase margin at 0dB > 70 deg. GLOOP dB margin at 0 deg. > 10 dB. Main characteristics

May 2015 DocID026206 Rev 1 1/30

AN4473Application note

PoE synchronous flyback, IEEE802.3at compliant, 5V - 4A PDconverter based on the PM8803 controller

Antonio Rotta

IntroductionThis document describes a reference design for a POE+, high efficiency, 5 V - 4 A flyback converter based on the PM8803 PoE controller.

The PM8803 is a highly integrated device embedding an IEEE802.3at compliant “Powered Device” (PD) interface together with a PWM controller and support for auxiliary sources.

The STEVAL-TSP004V2 reference design is based on an isolated flyback topology CCM converter with synchronous rectification with a gate driver transformer. The same PCB can be populated in different ways to support various configurations and topologies (the flyback with diode rectification, synchronous flyback with or without an active clamp, self-driven synchronous flyback).

Figure 1. STEVAL-TSP004V2 evaluation board photo

www.st.com

http://www.st.com

Contents AN4473

2/30 DocID026206 Rev 1

Contents

1 Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . . . 3

2 Schematics for 5 V at 4 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1 Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2 Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Measurements results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.1 Efficiency comparison with three rectification bridge options . . . . . . . . . . 13

3.2 Converter efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.3 Voltage ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.4 Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.5 Primary side waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.6 Secondary side waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.7 Load transients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.8 PoE to auxiliary switchover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.9 Gloop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4 Supporting material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.1 PCB layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

5 Electrical diagram general . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

DocID026206 Rev 1 3/30

AN4473 Main characteristics and circuit description

30

1 Main characteristics and circuit description

The main characteristics (reference and electrical specifications) of the converter are listed inTable 1 and Table 2.

This document details the characteristics and performances of the PM8803 evaluation kit STEVAL-TSP004V2, which has been designed to cover a broad range of Power over Ethernet (PoE) applications.

The PM8803 is a highly integrated device embedding an IEEE802.3af/at compliant powered device (PD) interface together with a PWM controller and support for auxiliary sources.

Even though the PM8803 device can be configured to work in several isolated topologies, self-driven or a transformer gate driven; this application note focuses on a high efficiency isolated flyback converter topology with synchronous rectification, 5 V output voltage with a 4 A output current capability.

Auxiliary sources can be connected to the board on 2 different input connectors. One input (AUX II) allows prevalence of the auxiliary sources with respect to the PoE, while the other input (AUX I) allows the usage of a wall adaptor with voltage lower than the internal PoE UVLO threshold and still benefits from the inherent inrush and DC current limit.

Table 1. Reference

Reference code

Device PM8803

Evaluation board STEVAL-TSP004V2

Table 2. Electrical specification

Parameter Specifications

Input voltage supplies VIN [VDC] From 40 to 60 V

Auxiliary input voltage range From 30 to 60 V

Output voltage Vout [VDC] 5 VDC ± 5% at 4 A

Peak-to-peak output ripple < 30 mVpp

Efficiency DC-DC at full load > 92%

Efficiency overall at full load > 89%

Transient response ΔVoutpk to 50% load step < 180 mV

ΔVout in load line case < 0.5%

GLOOP bandwidth > 3 kHz

GLOOP phase margin at 0dB > 70 deg.

GLOOP dB margin at 0 deg. > 10 dB

Main characteristics and circuit description AN4473

4/30 DocID026206 Rev 1

The possible configurations supported by the PM8803 demonstration kit as options on the same PCB are:

• Alternative input bridge rectification: 4 possible options including standard diode bridges, discrete schottky diode bridges, half active bridges and full active bridges; schottky diode bridges are mounted on this eval board.

• Optional 4 pairs detection circuit, to detect if power is provided on 2 pairs or on 4 pairs by a high power PSE source; this circuit is not used on this eval board.

• Optional booster circuit, to increase the max. input current over 1 A; this circuit is not used on this eval board.

• Diode or synchronous rectification; 4 package options for the diode and 2 package options for the MOSFET.

• Primary side snubber; 3 options included an active clamp: a simple R-C snubber is used on this eval board.

• Power transformer; 3 size options for transformer gate driven solutions and 2 size options for self-driven applications.

The bill of material (BOM) in Table 3 provides the list of components to be mounted to obtain a flyback CCM converter with a gate transformer driven synchronous rectifier, with 5 V output at a 4 A evaluation board.

DocID026206 Rev 1 5/30

AN4473 Schematics for 5 V at 4 A

30

2 Schematics for 5 V at 4 A

2.1 Schematic

Figure 2. STEVAL-TSP004V2 evaluation board: electrical schematic (1/2)

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Schematics for 5 V at 4 A AN4473

6/30 DocID026206 Rev 1

Figure 3. STEVAL-TSP004V2 evaluation board: electrical schematic (2/2)

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DocID026206 Rev 1 7/30


30

2.2 Bill of material

Table 3. Bill of material

Item Ref. Description Value PCB footprint Supplier Voltage

1 C5 Ceramic Capacitor 10 nF 10% C0603 TDK 100 V




5 C9 Ceramic Capacitor 2.2 nF C1812 AVX 2 kV




9 C18 Ceramic Capacitor 0.1 µF 10% C0805 TDK 100 V

10 C19 Ceramic Capacitor 10 nF C0603 Several 50 V


12 C22 Ceramic Capacitor TBD C1812 AVX 2 kV

13 C23 Ceramic Capacitor 470 nF 10% C0603 Several 50 V

14 C26 Aluminium capacitor 33 µF 20% C-POL8-10 Panasonic -

EEEFK2A330P100 V

15 C27 Ceramic Capacitor 22 µF C1206Murata -

GRM31CR61C226ME15L

16 V

16 C28 Ceramic Capacitor 2.2 µF C1210Murata -

GRM32ER72A225KA35L

100 V

17 C29 Ceramic Capacitor 2.2 µF C1210Murata -

GRM32ER72A225KA35L

100V

18 C30 Ceramic Capacitor 68 pF C0805 TDK 100 V

19 C31 Ceramic Capacitor 1.5 nF C0805 Several 50 V


GRM31CR61C226ME15L

16 V

21 C34 Aluminium capacitor 330 µF C-POL8-10 Panasonic -

EEEFK1C331P16 V


GRM31CR61C226ME15L

16 V

23 C36 Ceramic Capacitor 0.1 µF C0603 Several 50 V


GRM31CR61C226ME15L

16 V


8/30 DocID026206 Rev 1


26 C39 Ceramic Capacitor 1 µF C0603 KEMET 25 V






32 C49 Ceramic Capacitor 3.3 nF C0603 Several 50 V



35 C54 Ceramic Capacitor 470 pF C0603 Several 50 V

36 C55 Ceramic Capacitor 100 pF C0603 Several 50 V



39 C60 Ceramic Capacitor 1 nF C0805 TDK 100 V


41 C64 Ceramic Capacitor 2.2 µF C1210MURATA -

GRM32ER72A225KA35L

100 V


GRM31CR61C226ME15L

16 V


GRM31CR61C226ME15L

16 V


45 D1 Diode STTH302S SMC STMicroelectronics

46 D4 Schottky Diode STPS2H100A SMA STMicroelectronics




50 D11 TVS diode SMAJ58A SMA STMicroelectronics





55 D20 Diode LED Aux det KA-3528SGT Kingbright

Table 3. Bill of material (continued)


DocID026206 Rev 1 9/30


30

56 D21 Diode STTH302S SMC STMicroelectronics

57 D26 Diode LED Out det KA-3528SGT Kingbright

58 D28 Schottky Diode BAT46J SOD323 STMicroelectronics

59 D32 Zenere Diode MM3Z15VT1 SOD323 Onsemi





64 D44 Diode LED T2P det KA-3528SGT Kingbright



67 JM1 Connector Jumper-doppio 3PIN-P254 Several

68 JM2 Connector Jumper-doppio 3PIN-P254 Several

69 J1 Connector SA P-JACK-RAPC722 Several

70 J2 Connector SP P-JACK-RAPC722 Several

71 J3 Connector DATA & POWER INPUT RJ45-8PIN Molex

72 J4 Connector DATA OUTPUT RJ45-8PIN Molex

73 J5 Connector MOR-10X10.5-P5-2PIN MOR-2POLI-508 Several

74 L5 Inductor 10uH MSS7341-103ML Coilcraft

75 L6 Inductor 0.33uH DO1813H Coilcraft

76 Q12 Mosfet STL60N3LLH5 PowerFLAT™ 5x6 STMicroelectronics

77 Q16 Mosfet MMBT3906LT1 SOT23 Several

78 Q17 Mosfet Si4848DY so8pwrpak-SO8 VISHAY

79 Q18 Mosfet MMBT3904LT1 SOT23 Several

80 R1 Resistor 75R R0603 Several




84 R9 Resistor 1K 1% R0603 Several





89 R17 Resistor 0R0 R0805 Several





10/30 DocID026206 Rev 1



93 R27 Resistor 27k R0603 Several

94 R32 Resistor 15K R0805 Several


96 R38 Resistor 1k R0603 Several


98 R44 Resistor 3K3 R0603 Several

99 R45 Resistor 24.9K R0603 Several



102 R52 Resistor 3K3 R0603 Several














116 R90 Resistor 1k5 R0603 Several





121 R95 Resistor 24.9K 1% R0603 Several







DocID026206 Rev 1 11/30


30



128 R108 Resistor 0.30 ohm 1% R1206 Bourns

129 R109 Resistor 0.30 ohm 1% R1206 Bourns







136 R131 Resistor 30R9 1% R0805 Several

137 TP2 Test Point Red TH-5013 Keystone

138 TP3 Test Point BLACK TH-5013 Keystone





















159 T1 Data Transfo ETH1-460 ETH1-460 Coilcraft

160 T5 Power Transfo COILCRAFT HA3691-AL PA2328NL Coilcraft




12/30 DocID026206 Rev 1

161 T8 Power Transfo COILCRAFT DA2319-AL DA2318-AL Coilcraft

162 U1 Controller IC PM8803 HTSSOP20-LARGE STMicroelectronics

163 U2 Optocoupler Fairchild FOD817AS FOD817 Fairchild


165 U4 Voltage Reference TS431AILT SOT23-5L STMicroelectronics




DocID026206 Rev 1 13/30

AN4473 Measurements results

30

3 Measurements results

3.1 Efficiency comparison with three rectification bridge optionsSTEVAL-TSP004V2 provides different rectification bridge options: single Schottky diode, half active bridge, full active bridge and diode bridge. They are alternatively usable thanks the options available on the STEVAL-TSP004V2 demo’s PCB. Efficiency measurements have been executed to compare the different characteristics cost/efficiency through three different rectification bridge options. Here below the schematics:

Figure 4. Schematic Schottky bridge

Figure 5. Schematic full active bridge

R37

0R01206

R3215K0805

D13

STPS2H100ASMA

R26

0R01206

D8

STPS2H100ASMA

TP2

Red

C15NM

0805

TP3

BLACK

D12

STPS2H100ASMA

D14

STPS2H100ASMA

D17

STPS2H100ASMA

D9

STPS2H100ASMA

D4

STPS2H100ASMA

D1

STTH302SSMC

J2

SP

1

2

3

D7STPS2H100ASMA

T1 pin.4 T1 pin.10T1 pin.1 T1 pin.7SP

POE+F

VSS

AUX 1

C77

NM

R291M

0603

Q4

P-Ch. 100VSO8

4

51

6 7 8

2 3

R37

0R01206

R20

200K

0603

C75NM

R19200K0603

D3

MM3Z15VT1SOD323

R34

1M

0603

R281M

0603R31

1M0603

R26

0R01206

R32

15K

0805

Q7

N-Ch. 100VSO8

4

51 2 3

6 7 8

R40

200K

0603

R25200K0603

R39

200K0603

C79NM

D6MM3Z15VT1

SOD323

R30

1M0603

R361M

0603

D2

MM3Z15VT1SOD323

Q1

P-Ch. 100VSO8

4

51

6 7 8

2 3

C73NM

D15

MM3Z15VT1SOD323

C15

NM

0805

R42200K0603

C78NM

D18

MM3Z15VT1SOD323

D19

MM3Z15VT1SOD323

D5

MM3Z15VT1SOD323

C72NM

Q5N-Ch. 100V

SO8

4

51 2 3

6 7 8

TP3

BLACK

Q6

N-Ch. 100VSO8

4

51 2 3

6 7 8

D16

MM3Z15VT1SOD323

R41200K0603

R351M0603

R33

1M

0603

C76

NM

C74NM

TP2

Red

D1

STTH302SSMC

Q2

P-Ch. 100VSO8

4

51

6 7 8

2 3

J2

SP

1

2

3

Q3P-Ch. 100V

SO8

4

51

6 7 8

2 3

R22

200K0603

Q8N-Ch. 100V

SO8

4

51 2 3

6 7 8

SP

T1 pin.4 T1 pin.10

T1 pin.1 T1 pin.7

POE+F

VSS

AUX 1

Measurements results AN4473

14/30 DocID026206 Rev 1

Figure 6. Schematic half active bridge

The measurement has been executed providing a 48V on the RJ45 connector and connecting the Poe+/Vss (TP22 vs TP23) with external electronic load with different current values to cover around 40W of input power.

Figure 7. Comparison efficiency bridge

Figure 7 shows the input stage efficiency comparison with three different bridge rectification type. The green line shows the efficiency of the Schottky diode bridge option, the cheaper of them, populated with four Schottky diodes STPS2H100A of each bridge. The yellow line shows the efficiency of the full active bridge, the most efficient, using two 100 V- 240 mΩ P-channel MOSFET on high side and two 100V 65 mΩ N-channel MOSFET on low side of each bridge. The red line shows the half active bridge solution, which represent a right compromise in term of cost vs. efficiency.

R26

0R01206

R331M

0603

C76NM

D7

STPS2H100ASMA

C15NM

0805

R40

200K0603

R42

200K0603

C78NM

TP2

Red

R39200K0603

Q6

N-Ch. 100VSO8

4

51 2 3

6 7 8 Q8

N-Ch. 100VSO8

4

51 2 3

6 7 8

R41200K0603

J2

SP

1

2

3

R34

1M

0603

R361M

0603

D1

STTH302SSMC

D16MM3Z15VT1SOD323

D18

MM3Z15VT1SOD323

Q5N-Ch. 100V

SO8

4

51 2 3

6 7 8

C79NM

D8

STPS2H100ASMA

D15

MM3Z15VT1SOD323

R37

0R01206

C77NM

D4

STPS2H100ASMA

TP3

BLACK

R32

15K

0805

R35

1M0603

D19

MM3Z15VT1SOD323

D9

STPS2H100ASMA

Q7N-Ch. 100V

SO8

4

51 2 3

6 7 8

SP

T1 pin.4 T1 pin.10T1 pin.1 T1 pin.7

VSS

POE+F

AUX 1

96.0%

96.5%

97.0%

97.5%

98.0%

98.5%

99.0%

99.5%

100.0%

0

100

200

300

400

500

600

700

800

Efficiency [%]

Input Current [mA]

Efficiency Data Transfo + Bridge

Schottky Diode Bridge

Full Active Bridge

Half Active Bridge

DocID026206 Rev 1 15/30


30

Changing the input bridge it is possible to gain up to 2% about on the overall converter efficiency.

3.2 Converter efficiency

Figure 8. Overall and DC/DC efficiency

Figure 8 shows overall and DC/DC efficiencies for the converter at 48Vindc.

The dotted green line is the STEVAL-TSP004V2 DC-DC efficiency. The measurement has been executed supplying 48 V to the input RJ45 connector J1 and measuring the input voltage by TP22/TP23, input voltage of DC-DC converter stage. Figure 8 shows also the overall efficiency comparison measured with the same DC-DC converter stage connected to the three different rectification bridge stages previously mentioned.

Please note that:

• Overall efficiency includes all loss from RJ45 to the output voltage rail.

• DC/DC efficiency is a figure of merit of the converter standalone and typically does not include the losses associated to the PoE interface section that are: the RJ45 connector, data transformer, bridges, power consumption of the I/F of the PM8803 device.

On the STEVAL-TSP004V2 evaluation board is mounted the simple Schottky diodes bridge solution (green line).

Thanks to the bridge rectification options foreseen on the pcb it is then possible to select the best compromise cost/efficiency depending on the target request.

86%

87%

88%

89%

90%

91%

92%

93%

94%

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Efficiency

Iout [mA]

5 Vout Overall and DC/DC Efficiency

Overall with Schottky

Overall FAB

Overall HAB

DC-DC


16/30 DocID026206 Rev 1

Figure 9. Output voltage drift

5.155

5.160

5.165

5.170

0.0 1.0 2.0 3.0 4.0

Output Voltage

Iout [mA]

5 Vout changhe with load

drift 5V at 48V

DocID026206 Rev 1 17/30


30

3.3 Voltage ripple

Above measurements are referred at the output voltage ripple.

In Figure 12 and Figure 13 a measure of the ripple on the input voltage has been done, to give an indication of the noise at the input of the converter.

Figure 10. Ripple on 5 V at 0.4 A Figure 11. Ripple on 5 V at 4 A

CH2: output currentCH4: output voltage


Figure 12. Ripple before and after input filter with 5 V at 0.4 A (measured on C26 and C28)

Figure 13. Ripple before and after input filter with 5 V at 4 A (measured on C26 and C28)

CH1: ripple after input filter

CH2: input currentCH3: ripple before input filter

CH4: primary Vgate

CH1: ripple after input filter

CH2: input currentCH3: ripple before input filter

CH4: primary Vgate


18/30 DocID026206 Rev 1

3.4 Startup

Figure 14. Startup from Microsemi 9001G injector - 5 V at 0.4 A

Figure 15. Startup from Microsemi 9001G injector - 5 V at 4 A

CH1: VCCCH2: input current

CH3: VSS - RTNCH4: output voltage

CH1: VCCCH2: input current


Figure 16. Startup from Microsemi 9501G injector- 5 V at 0.4 A

Figure 17. Startup from Microsemi 9501G injector- 5 V at 4 A

CH1: Tx Rx input currentCH2: spare input current


CH1: Tx Rx input currentCH2: spare input current


DocID026206 Rev 1 19/30


30

Figure 18. Detail of the output voltage at startup with no load

Figure 19. Detail of the output voltage at startup with 4 A load

CH2: input currentCH4: output voltage

CH2: input currentCH4: output voltage


20/30 DocID026206 Rev 1

3.5 Primary side waveforms

Figure 20. Primary steady state 0.4 A Figure 21. Primary steady state 4 A

CH1: primary MOSFET drain

CH2: input currentCH4: primary MOSFET gate

CH1: primary MOSFET drain

CH2: input currentCH4: primary MOSFET gate

Figure 22. Detail of primary drain at 4 A load

CH1: primary MOSFET drainCH2: input current

CH4: primary MOSFET gate

DocID026206 Rev 1 21/30


30

3.6 Secondary side waveforms

Figure 23. Secondary steady state 0.4 A Figure 24. Secondary steady state 4 A

CH1: secondary MOSFET drainCH2: input current

CH4: secondary MOSFET gate



Figure 25. Detail of secondary drain at 4 A load




22/30 DocID026206 Rev 1

3.7 Load transients

3.8 PoE to auxiliary switchover

In Figure 28 is shown a smooth transition from a PoE line set to 54 V toward an auxiliary adapter at 44 V; the output voltage is maintained stable during the transition.

Figure 26. 2 A - 4 A load transient Figure 27. 0.4 A - 4 A load transient



Figure 28. PoE to auxiliary switchover

CH1:converter input voltage

CH2: PoE input currentCH3: T2P signal

CH4: output voltage

DocID026206 Rev 1 23/30


30

3.9 Gloop

Figure 29. Gloop 48 V at 4 A Figure 30. Gloop 48 V at no load

Bw: 3.2 KHzGM:10.6 dBPM: 70 deg.

Bw: 4.0 KHzGM:12.2 dBPM: 77 deg.

Figure 31. Gloop 40 V at 4 A Figure 32. Gloop 57 V at no load

Bw: 3.2 KHz

GM:10.6 dBPM: 70 deg.

Bw: 4.2 KHz

GM:11.7 dBPM: 78 deg.

Supporting material AN4473

24/30 DocID026206 Rev 1

4 Supporting material

4.1 PCB layers

Figure 33. PCB top assembly

Figure 34. PCB bottom assembly

DocID026206 Rev 1 25/30

AN4473 Supporting material

30

Figure 35. PCB layer 1 top

Figure 36. PCB layer 2

Supporting material AN4473

26/30 DocID026206 Rev 1

Figure 37. PCB layer 3

Figure 38. PCB layer 4 bottom

DocID026206 Rev 1 27/30

AN4473 Electrical diagram general

30

5 Electrical diagram general

Figure 39. Schematic 1 of 2 (general)

Q3

SO

8

4

51678

23

D1

STT

H30

2SS

MC

D25

<Des

crip

tion>

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0603

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0603

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51678

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ETH

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Cha

ssis

Cha

ssis

Cha

ssis

Cha

ssis

Cha

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pairs

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tion

sign

al

Electrical diagram general AN4473

28/30 DocID026206 Rev 1

Figure 40. Schematic 2 of 2 (general)

Q1

9

MM

BT3

90

4LT

1

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TP9

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d

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DocID026206 Rev 1 29/30

AN4473 Revision history

30

6 Revision history

Table 4. Document revision history

Date Revision Changes

25-May-2015 1 Initial release.

AN4473

30/30 DocID026206 Rev 1

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PoE synchronous flyback, IEEE802.3at compliant, 5V - 4A PD ... · GLOOP bandwidth > 3 kHz GLOOP phase margin at 0dB > 70 deg. GLOOP dB margin at 0 deg. > 10 dB. Main characteristics