TN FC 35: E·MMC PCB Design Guide TNFC35 E MMC

Technical Note

e·MMC PCB Design Guide

Introduction

This document is intended as guide for PCB designers using Micron e·MMC devices

and will discuss the primary issues affecting design and layout.

Figure 1: e·MMC 4.5 and 5.0 Package Compatibility

RFU

DAT7

VCCQ

VCC

RFU

CLK

NC

VSSQ

NC

A

B

C

D

E

F

G

H

J

K

L

M

N

P

NC

DAT3

VDDIM

NC

VSSQ

NC

DAT0

DAT4

NC

RFU

NC

VCCQ

DAT1

DAT5

VSSQ

NC

VCCQ

VSSQ

DAT2

DAT6

RFU

VCC

VSS

RFU

RST_n

CMD

VSSQ

VCCQ

NC

RFU

NC

VSS

RFU

NC

RFU

NC

RFU

VSS

NC

RFU

VCC

NC

RFU

VSS

VCC

RFU

NC

RFU

NC

1 2 3 4 5 6 7 8 9 10 11 12 13 14

A

B

C

D

E

F

G

H

J

K

L

M

N

P

A

B

C

D

E

F

G

H

J

K

L

M

N

P

1

NC

1

2

NC

DAT3

V

DDI

NC

V

SSQ

NC

2

3

DAT0

DAT4

NC

V

CCQ

3

4

DAT1

DAT5

V

SSQ

NC

V

CCQ

V

CCQ

V

SSQ

4

5

DAT2

DAT6

NC

RFU

V

CC

V

SS

DS

V

SS

RST_n

CMD

V

SSQ

V

CCQ

5

6

V

SS

DAT7

V

CCQ

V

CC

RFU

CLK

NC

V

SSQ

6

7

RFU

NC

V

SS

RFU

NC

7

8

NC

RFU

V

SS

NC

8

9

NC

RFU

V

CC

NC

9

10

NC

RFU

V

SS

V

CC

RFU

NC

RFU

10

11

NC

11

12

NC

12

13

NC

13

14

NC

14

Ball e·MMC 4.51 e·MMC 5.0 Comment

H5 RFU DS DS can be floating if HS400 is not used.

A6, J5 RFU VSS VSS can be floating if HS400 is not used.

C5 RFU NC Used for routing in this technical note only

because it is NC internally, and JEDEC rede-

fined it as NC for e·MMC 5.0.

TN-FC-35: e·MMC PCB Design Guide

Introduction

PDF: 09005aef85c3dc13

tnfc35_eMMC_pcb_design_guide.pdf - Rev. B 01/15 EN 1Micron Technology, Inc. reserves the right to change products or specifications without notice.

Products and specifications discussed herein are for evaluation and reference purposes only and are subject to change by

Micron without notice. Products are only warranted by Micron to meet Micron's production data sheet specifications. All

information discussed herein is provided on an "as is" basis, without warranties of any kind.

Figure 2: Host to Micron e·MMC 5.0 Connection

VCCQ

VCC

VCCQ

CLK

CMD

DS

DAT0

DAT1

DAT2

DAT3

DAT4

DAT5

DAT6

DAT7

RST_n

CLK

CMD

DS

DAT0

DAT1

DAT2

DAT3

DAT4

DAT5

DAT6

DAT7

RST_n VCC

VCCQ

VDDiM

VCC

R_CMD

R_DS

SR_DS

C1 C2

SR_CLK

GND

U2

Host controller

U1

e·MMC

R_DAT R_DAT R_DAT R_DAT R_DAT R_DAT R_DAT R_RST_nR_DAT

C3

C4

C5 C6

TN-FC-35: e·MMC PCB Design Guide

Introduction

PDF: 09005aef85c3dc13

tnfc35_eMMC_pcb_design_guide.pdf - Rev. B 01/15 EN 2Micron Technology, Inc. reserves the right to change products or specifications without notice.

Signal and Capacitor Placement

SR_CLK should be close to the host device, and SR_DS should be close to the e·MMC

device. e·MMC signals can be fanned out through NC pins. No internal connection is

present for NC pins. Micron recommends that e·MMC signals not be fanned out

through RFU pins.

The recommended decoupling capacitors should be placed on the bottom side of the

PCB across the BGA escape vias in order to minimize the connection inductance seen

by the capacitor. The capacitor pad should be connected to the power and ground

plane with a larger via to minimize the inductance in decoupling capacitors and allow

for maximum current flow. The recommended capacitor values are shown in Table 1

(page 4). Wide, short traces between the via and capacitor pads should be used, or

the via placed adjacent to the capacitor pad. Figure 4 (page 4) shows how to connect

capacitor pads to the power and ground plane. Method 1 is not recommended, while

the others are recommended.

Figure 3: Capacitor Placement and Signal PCB Layout

D0 D1 D2 VSS

VCCQ

VCC

VSSQ

VSS

CMDCLK

DS

RST_n

VDDi

D3 D4 D5 D6 D7

TN-FC-35: e·MMC PCB Design Guide

Signal and Capacitor Placement

PDF: 09005aef85c3dc13

tnfc35_eMMC_pcb_design_guide.pdf - Rev. B 01/15 EN 3Micron Technology, Inc. reserves the right to change products or specifications without notice.

Table 1: Component Parameter Values

Parameter Symbol Min Max

Recom-

mended Unit Comments

Pull-up resistance for CMD R_CMD 4.7 50 10 KΩTo prevent bus floating

Pull-up resistance for DAT[7:0] R_DAT 10 50 50 KΩTo prevent bus floating

Pull-up resistance for RST_n R_RST_n 4.7 50 50 KΩIt is not necessary to put pull-up

resistance on RST_n line if the

host does not use H/W reset.

Pull-down resistance for R_DS R_DS 4.7 50 50 KΩ

Impedance of CLK/CMD/DS/

DAT[7:0]

– 45 55 50 ΩImpedance match

Serial resistance on CLK line SR_CLK 0 47 22 ΩTo stabilize CLK signal

Serial resistance on DS line SR_DS 0 47 22 ΩTo stabilize DS signal

VCCQ capacitor value C1, C2 2.2 + 0.1 4.7 + 0.22 2.2 + 0.1 µF Decoupling capacitor should be

connected with VCCQ and VSSQ as

closely as possible.

VCC capacitor value (≤8GB) C3, C4 2.2 + 0.1 4.7 + 0.22 2.2 + 0.1 µF Decoupling capacitor should be

connected to VCC and VSS as close-

ly as possible.

VCC capacitor value (>8GB) 4.7 + 0.22 µF

VDDIM capacitor value C5, C6 1 + 0.1 4.7 + 0.1 1 + 0.1 µF Decoupling capacitor should be

connected to VDDIM and VSSQ as

closely as possible.

Figure 4: Connecting Capacitor Pads

Absolutely not!

1

Even better

3

Better still

4

The best!

Solid via within pad

5

Better

2

TN-FC-35: e·MMC PCB Design Guide

Signal and Capacitor Placement

PDF: 09005aef85c3dc13

tnfc35_eMMC_pcb_design_guide.pdf - Rev. B 01/15 EN 4Micron Technology, Inc. reserves the right to change products or specifications without notice.

PCB Topology and Layout

The PCB board must have at least four layers.

CLK, CMD, DQ and DS signals should be treated as transmission lines with controlled

impedance from 45Ω to 55Ω. The skew of propagation time of these signals should be

minimized and the PCB trace length difference kept within ±50 mil. The following figure

shows two commonly used PCB transmission line topologies.

Figure 5: Transmission Line Topologies

PCB Trace

Stripline

Ground Plane

Dielectric

Microstrip

The e·MMC signals' trace length should be as short as possible; it is best kept to less

than 2000 mil.

The transmission line should be designed so that the conductor is as close to the

ground plane as possible. This technique will couple the transmission line tightly to the

ground plane and help decouple it from adjacent signals. It's best to widen spacing be-

tween signal lines as much as routing restrictions will allow, trying not to bring traces

closer than three times the trace width.

Figure 6: Trace Width Example

W

Arc-shaped traces should be used instead of right-angle bends.

Figure 7: Trace Shape

Recommended RecommendedNot recommended

There should be NO breaks or voids in the ground plane under or over the high speed

signals.

TN-FC-35: e·MMC PCB Design Guide

PCB Topology and Layout

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tnfc35_eMMC_pcb_design_guide.pdf - Rev. B 01/15 EN 5Micron Technology, Inc. reserves the right to change products or specifications without notice.

Figure 8: Avoiding Breaks and Voids

Bad

Slot in image plane

Return

current

Better

Slot in image plane

Return

current

The best signaling is obtained when a constant reference plane is maintained. If a refer-

ence plane transition cannot be avoided, we recommend using the following techni-

ques.

• If the signal reference plane changes from ground plane to power plane, adding ca-

pacitors near the via transition site will help support a good return path.

• If the signal reference plane changes from ground plane to another ground plane,

ground vias should surround all high-speed signals (two ground vias per clock via;

one ground via per high speed signal via).

TN-FC-35: e·MMC PCB Design Guide

PCB Topology and Layout

PDF: 09005aef85c3dc13

tnfc35_eMMC_pcb_design_guide.pdf - Rev. B 01/15 EN 6Micron Technology, Inc. reserves the right to change products or specifications without notice.

Figure 9: Additional Capacitor for Return Current

MLCC

Ground

plane

Power plane

Trace

Stubs should be kept short to avoid reflections. Stub propagation delay should be kept

to <20% of the rise time of the signal.

Figure 10: Typical Stub Case

Branch

TN-FC-35: e·MMC PCB Design Guide

PCB Topology and Layout

PDF: 09005aef85c3dc13

tnfc35_eMMC_pcb_design_guide.pdf - Rev. B 01/15 EN 7Micron Technology, Inc. reserves the right to change products or specifications without notice.

Revision History

Rev. B – 01/15

• Updated the Host to Micron e·MMC 5.0 Connection figure

Rev. A – 08/14

• Initial release

8000 S. Federal Way, P.O. Box 6, Boise, ID 83707-0006, Tel: 208-368-4000

www.micron.com/products/support Sales inquiries: 800-932-4992

Micron and the Micron logo are trademarks of Micron Technology, Inc.

All other trademarks are the property of their respective owners.

TN-FC-35: e·MMC PCB Design Guide

Revision History

PDF: 09005aef85c3dc13

tnfc35_eMMC_pcb_design_guide.pdf - Rev. B 01/15 EN 8Micron Technology, Inc. reserves the right to change products or specifications without notice.

TN FC 35: E·MMC PCB Design Guide TNFC35 E MMC

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