AN6068 Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM.pdf

AN6068
Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM
Author: Shivendra Singh
Associated Project: No
Associated Part Family: CY14x104NA
Software Version: None
Related Application Notes: AN43593
To get the latest version of this application note, or the associated project file, please visit
http://www.cypress.com/go/AN6068.
AN6068 discusses the key pinout differences between the Everspin 4-Mbit (256K x 16) MRAM and the Cypress 4-Mbit
(256K x 16) nvSRAM devices. These differences should be taken into consideration when designing a PCB to use either
MRAM or the high performance nvSRAM on the same footprint as true alternate source part number on the same bill of
materials (BOM).
Introduction
Cypress offers the highest performance and most reliable
nonvolatile RAM products available with its nvSRAM
product line. The nvSRAM technology combines the
performance characteristics of a high-speed SRAM with
that of a nonvolatile memory. A similar nonvolatile solution
is the Magnetoresistive RAM (MRAM) from Everspin in
which magnetic polarization is used to store information.
This application note discusses designing applications
hardware with the option to use either MRAM or nvSRAM
on the same socket without any hardware redesign.
The nvSRAM requires a storage capacitor (VCAP) to
execute AutoStore. The VCAP pin on the nvSRAM package
corresponds to either a DC (Do Not Connect) or a NC (No
Connect) pin on the MRAM part depending upon package
type. The MRAM recommends that NC or DC pins can be
left either floating or tied to VSS. Therefore the storage
capacitor for nvSRAM can remain connected when
nvSRAM or MRAM are interchangeably used.
������ pin to monitor the device
The nvSRAM also has a HSB
������ pin on the
status or to initiate a hardware store. The HSB
nvSRAM package corresponds to a NC (No Connect) pin
on the MRAM package. This allows using MRAM and
nvSRAM interchangeably on the same footprint. In this
case the NC pin corresponding to ������
HSB can be either left
floating or can be connected to the VCC.
www.cypress.com
Additional on-demand nonvolatile features of nvSRAM
such as hardware initiated STORE through a hardware pin
������) or software initiated STORE and RECALL through
(HSB
soft sequences and so on, are specific to the nvSRAM
device and need not be considered while migrating from
MRAM to nvSRAM. However, an application can integrate
these additional features of nvSRAM to enhance their
application performance and flexibility. Refer to the
Cypress nvSRAM datasheets for using additional nvSRAM
features in your applications.
Replacing MRAM with Cypress
nvSRAM
This section highlights pin and package differences
between the Cypress nvSRAM and the MRAM devices for
4-Mbit (256K x 16) in 44-pin TSOP-II (Thin Small Outline
Package - Type II) and 48-ball FBGA (Fine Pitch Ball Grid
Array) package options respectively. This section also
discusses about necessary design considerations which
will enable you to create a common PCB footprint for
using either nvSRAM or MRAM on the same footprint.
Replacing 44 TSOP-II Package Option
Figure 1 shows an example of replacing 4-Mbit (x16)
MRAM by the 4-Mbit (x16) nvSRAM in a 44-pin TSOP-II
package option on the same 44 pad PCB footprint. The
dimensions of the 44-pin TSOP-II package of MRAM and
nvSRAM devices are identical and shown in Table 1.
Document No. 001-16633 Rev. *D
1
Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM
Table 1. 44-pin TSOP II Package Comparison
Package
Dimensions
MRAM
(Typ in mm)
The nvSRAM 44-pin TSOP-II pinout is similar to that of the
MRAM 44-pin TSOP-II pinout except for the pin 28, which
is designated as a DC (Do Not Connect) pin on the
MRAM, whereas it is the VCAP pin on the nvSRAM. By
creating a footprint option for connecting an appropriate
capacitor for nvSRAM VCAP, the MRAM can be easily
replaced by the nvSRAM, or the nvSRAM replaced by the
MRAM, without any modification to the board. Refer
Figure 3 for the nvSRAM VCAP connection.
nvSRAM
(Typ in mm)
Length
18.4
18.4
Width
10.16
10.16
Height
1.2
1.2
Pitch
0.8
0.8
Figure 1. MRAM and nvSRAM 44-pin TSOP II Package Comparison
A0
1
44
A17
A0
1
44
A17
A1
2
43
A16
A1
2
43
A16
A2
3
42
A15
A2
3
42
A15
A3
4
41
OE
A3
4
41
G
A4
5
40
UB
A4
5
40
BHE
E
6
39
LB
CE
6
39
BLE
DQL0
7
38
DQU15
DQ0
7
38
DQ15
DQL1
8
37
DQU14
DQ1
8
37
DQ14
DQL2
9
36
DQU13
DQ2
9
36
DQ13
DQL3
10
35
DQU12
DQ3
10
VDD
11
34
VSS
VCC
11
VSS
12
33
VDD
VSS
DQL4
13
32
DQU11
DQL5
14
31
DQU10
DQL6
15
30
DQL7
16
W
17
MRAM
44- pin TSOP II
(x16)
35
DQ12
34
VSS
12
33
VCC
DQ4
13
32
DQ11
DQ5
14
31
DQ10
DQU9
DQ6
15
30
DQ9
29
DQU8
DQ7
16
29
DQ8
28
DC
WE
17
28
VCAP
18
27
A14
44- pin TSOP II
(x16)
A5
18
27
A14
A5
A6
19
26
A13
A6
19
26
A13
A7
20
25
A12
A7
20
25
A12
A8
21
24
A11
A8
21
24
A11
A9
22
23
A10
A9
22
23
A10
Replacing 48-ball FBGA Package Option
Figure 2 shows an example of replacing 4-Mbit (x16)
MRAM by a 4-Mbit (x16) nvSRAM in a 48-ball FBGA
package option on the same 48 pad PCB footprint. The
dimensions of 48-ball FBGA package of MRAM and
nvSRAM devices differ in their length, width, and height.
However the pitch of the 48-ball FBGA package remains
identical which makes it possible to create a drop in
replacement footprint for both package options. In this
case, the package keep-out area on the PCB should be
maintained such that either nvSRAM or MRAM 48-ball
FBGA package can be mounted easily without obstructing
other components on the PCB. The comparison of 48-ball
FBGA package dimension for MRAM and nvSRAM are
shown in Table 2.
www.cypress.com
nvSRAM
Table 2. 48-ball FBGA Package Comparison
Package
Dimensions
MRAM
(Typ in mm)
nvSRAM
(Typ in mm)
Length
8
10
Width
8
6
Height
1.35
1.2
Pitch
0.75
0.75
Document No. 001-16633 Rev. *D
2
Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM
The nvSRAM pinout is similar to that of the MRAM except
for the three balls E3, G2, and H6 which are either
designated as a DC (Do Not Connect) or NC (No Connect)
pin for the MRAM. Whereas E3, G2, and H6 are the VCAP,
������), and NC pin for the nvSRAM respectively. By
(HSB
creating a footprint option for connecting an appropriate
capacitor for nvSRAM VCAP, the MRAM can be easily
replaced by the nvSRAM, or the nvSRAM replaced by the
MRAM, without any modification to the board. The
nvSRAM ������
HSB pin is pulled to HIGH internally by a weak
pull up resistor (~100 KΩ). Therefore, if the nvSRAM
������) pin functionality is not used in the design, the (HSB
������)
(HSB
pin can be left as floating (NC). There is no restriction for
nvSRAM NC pin connection. The nvSRAM NC pin can be
biased to any logic level (HIGH or LOW) or can be left as
floating (NC) in the design. Refer to Figure 3 for the
������) connection.
nvSRAM VCAP and (HSB
Figure 2. MRAM and nvSRAM 48-ball FBGA Package Comparison
MRAM 48-ball FBGA (x16)
nvSRAM 48-ball FBGA (x16)
1
2
3
4
5
6
LB
G
A0
A1
A2
NC
DQU8
UB
A3
A4
E
DQU9
DQU10
A5
A6
VSS
DQU11
A17
VDD
DQU12
DQU14
1
2
3
4
5
6
A
BLE
OE
A0
A1
A2
NC
A
DQL0
B
DQ8
BHE
A3
A4
CE
DQ0
B
DQL1
DQL2
C
DQ9
DQ10
A5
A6
DQ1
DQ2
C
A7
DQL3
VDD
D
VSS
DQ11
A17
A7
DQ3
VCC
D
NC
A16
DQL4
VSS
E
VCC
DQ12
VCAP
A16
DQ4
VSS
E
DQU13
A14
A15
DQL5
DQL6
F
DQ14
DQ13
A14
A15
DQ5
DQ6
F
DQU15
NC
A12
A13
W
DQL7
G
DQ15
HSB
A12
A13
WE
DQ7
G
NC
A8
A9
A10
A11
DC
H
NC
A8
A9
A10
A11
NC
H
Figure 3. nvSRAM VCAP and ������
HSB Connection
VCC
10K Ohm
Note 1
Pull up
(Optional)
HSB
nvSRAM
To Controller I/O
(Optional)
VCAP
C
Note 2
������ can be left floating (or NC) if its functionality is not used in the design. It is recommended to
Note 1: The nvSRAM HSB
������ pin if this pin is connected to a controller I/O for its control.
connect an external pull-up resistor of 4.7KΩ-10KΩ on the HSB
Note 2: The capacitor (C) on the nvSRAM VCAP pin can be specified as DNI (Do Not Install) in the BOM while using MRAM
instead of nvSRAM on the same footprint. The capacitor (C) should be installed when using the nvSRAM. Refer AN43593 for
selecting an appropriate VCAP.
www.cypress.com
Document No. 001-16633 Rev. *D
3
Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM
Other System Design Considerations
The nvSRAM’s power circuitry is robustly designed to
maintain its data integrity across all types of power supply
ramp rates or brown out conditions which can be observed
in a system setup. The nvSRAM does not put any
condition on its power-up and power-down behavior. The
follow on sections explain nvSRAM behavior during
power-up and power-down cycles.
Power Up
When the nvSRAM VCC power supply crosses an internal
threshold (VSWITCH) level, the device starts boot-up
sequence followed by memory RECALL, which recalls
user data from its nonvolatile memory cell to SRAM and
becomes ready for the access. The nvSRAM takes
maximum 20 ms (tHRECALL) to complete its boot-up
sequence before the controller can access the part. The
nvSRAM’s I/Os remains disabled during tHRECALL time
therefore none of the I/Os require tracking to the power
supply during power-up as in the case of MRAM. The
� and W
� ) to track the
MRAM requires its control signals (E
power supply during power-up and must be held high for a
2 ms start-up period after the power supply reaches the
MRAM minimum operating voltage (VDD min).
The nvSRAM recommends a 4.7 kΩ - 10 kΩ pull-up
�����) control line to avoid any
resistor on its write enable (WE
unwanted write in case if controller is still booting-up and
its I/Os remain tri-stated or floating while nvSRAM
becomes ready after its boot-up cycle. This issue is also
applicable to MRAM if the device is not write-protected
properly in case of floating controller I/Os. Data corruption
due to unwanted write in MRAM is permanent and
irreversible, whereas it is reversible in case of nvSRAM.
The nvSRAM retains a copy of the most recently stored
user data in its nonvolatile memory which is recalled to the
SRAM portion of the memory cell during power-up recall,
therefore the host controller can easily recover the original
data by executing software RECALL and replace the
corrupted SRAM data with correct user data.
www.cypress.com
Power Down
When the nvSRAM VCC power supply falls below (VSWITCH)
threshold, the device initiates the AutoStore operation
internally using stored charge on the small capacitor
connected to its VCAP pin. When the nvSRAM loses VCC
power when a write cycle has been initiated and is still in
progress, the write cycle will be allowed to complete
before data transfer from the SRAM portion of the cells to
nonvolatile elements begins. This ensures that the last
data word successfully written to the nvSRAM is saved
during AutoStore. Once an AutoStore cycle starts in the
nvSRAM, the I/Os are disabled and internal circuitry
automatically switches from VCC power to the VCAP power
source.
Summary
Cypress nvSRAM’s pinout is similar to the MRAM pinout
except for the VCAP pin which is typically a no connect
(NC) pin in MRAM. Customers using a MRAM can easily
migrate to nvSRAM by designing a provision on the PCB
to connect a capacitor on the VCAP pin. The capacitor can
be left in place when MRAM is used on the board with no
influence on the MRAM. Including VCAP allows nvSRAM
and MRAM to be used as alternate sources in applications
requiring NVRAM performance. The remainders of the
pins provide identical functionalities for both MRAM and
nvSRAM.
About the Author
Name:
Shivendra Singh
Title:
Applications Engineer Principal
Document No. 001-16633 Rev. *D
4
Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM
Document History
Document Title: Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM - AN6068
Document Number: 001-16633
Revision
ECN
Orig. of
Change
Submission
Date
**
1200303
ZSK
06/29/2007
*A
3125574
ZSK
01/02/2011
*B
3756324
ZSK
09/27/2012
Description of Change
Obtain spec# for note to be added to spec system. This note had no technical
updates. Kindly replace existing .pdf file on http://www.cypress.com.
Updated Introduction.
Updated in new template.
Added section “Other System Design Considerations”.
Updated Summary.
Updated template.
Updated Abstract to include 4-Mbit specific description.
*C
3908795
ZSK
02/20/2013
Added package dimension tables (Table 1 and Table 2).
Included 48-ball FBGA package option.
Update the title to “Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM”.
*D
4677354
www.cypress.com
KAHA
03/03/2015
Updated the document as per new template.
Corrected Figure 1.
Document No. 001-16633 Rev. *D
5
Replacing 4-Mbit (256K x 16) MRAM with Cypress nvSRAM
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Document No. 001-16633 Rev. *D
6