19-2134; Rev 3; 1/08
SPI-Compatible RTC in a TDFN
General Description
The MAX6902 SPI™-compatible real-time clock con-
tains a real-time clock/calendar and 31 x 8 bits of static
random-access memory (SRAM). The real-time
clock/calendar provides seconds, minutes, hours, day,
date, month, year, and century information. A time/date
programmable polled ALARM is included in the
MAX6902. The end-of-the-month date is automatically
adjusted for months with fewer than 31 days, including
corrections for leap year up to the year 2100. The clock
operates in either the 24hr or 12hr format with an
AM/PM indicator. The MAX6902 operates with a supply
voltage of +2V to +5.5V, is available in the ultra-small
8-pin TDFN package, and works over the -40°C to
+85°C industrial temperature range.
Features
♦
Real-Time Clock Counts Seconds, Minutes, Hours,
Day of Week, Date of Month, Month, Year, and Century
♦
Leap-Year Compensation Valid up to Year 2100
♦
+2V to +5.5V Wide Operating Voltage Range
♦
SPI Interface: 4MHz at 5V; 1MHz at 2V
♦
31 x 8-Bit SRAM for Scratchpad Data Storage
♦
Uses Standard 32.768kHz, 12.5pF Watch Crystal
♦
Low Timekeeping Current (400nA at 2V)
♦
Single-Byte or Multiple-Byte (Burst Mode) Data
Transfer for Read or Write of Clock Registers or
SRAM
♦
Ultra-Small 8-Pin 3mm x 3mm x 0.8mm TDFN
Package
♦
Programmable Time/Date Polled ALARM Function
♦
No External Crystal Bias Resistors or Capacitors
Required
MAX6902
Applications
Point-of-Sale Equipment
Intelligent Instruments
Fax Machines
Battery-Powered Products
Portable Instruments
Ordering Information
PART
MAX6902ETA+T
TEMP RANGE
-40°C to +85°C
PIN-
PACKAGE
8 TDFN
TOP
MARK
+AGT
+Denotes
lead-free package.
Related Real-Time Clock Products
PART
MAX6900
MAX6901
MAX6902
SERIAL
INTERFACE
I
2
C compatible
3 Wire
SPI compatible
SRAM
31
✕
8
31
✕
8
31
✕
8
ALARM
FUNCTION
—
Polled
Polled
OUTPUT
FREQUENCY
—
32kHz
—
PIN-
PACKAGE
6 TDFN
8 TDFN
8 TDFN
Typical Operating Circuit
+3.3V 0.1μF
6
+3.3V
V
CC
X1
8
32.768kHz
CRYSTAL
Pin Configuration
TOP VIEW
+
SCLK
DOUT
DIN
1
2
8
7
X1
X2
V
CC
CS
MAX6902
1
SCLK
CS
DOUT
DIN
GND
4
μc
5
2
3
X2
7
MAX6902
3
6
5
EXPOSED PADDLE
GND 4
TDFN
SPI is a trademark of Motorola, Inc.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
SPI-Compatible RTC in a TDFN
MAX6902
ABSOLUTE MAXIMUM RATINGS
V
CC
to GND ..............................................................-0.3V to +6V
All Other Pins to GND ................................-0.3V to (V
CC
+ 0.3V)
Current into Any Pin..........................................................±20mA
Rate of Rise, V
CC
............................................................100V/µs
Continuous Power Dissipation (T
A
= +70°C)
8-Pin TDFN (derate 24.4mW/°C above +70°C) ..........1951.0mW
Junction Temperature .....................................................+150°C
Storage Temperature Range…………………… -65°C to +150°C
ESD Protection (all pins, Human Body Model) ..................2000V
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(V
CC
= +2.0V to +5.5V, T
A
= -40°C to +85°C. Typical values are at V
CC
= +3.3V, T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
Operating Voltage
Range
Active Supply Current
(Note 2)
Timekeeping Supply
Current (Note 3)
SYMBOL
V
CC
I
CC
V
CC
= +2V
V
CC
= +5V
V
CC
= +2V
I
TK
V
CC
= +3.6V
V
CC
= +5V
SPI DIGITAL INPUTS (SCLK, DIN,
CS)
Input High Voltage
Input Low Voltage
Input Leakage Current
Input Capacitance
SPI DIGITAL OUTPUTS (DOUT)
Output Capacitance
Output Low Voltage
Output High Voltage
V
OL
V
OH
V
CC
= +2.0V, I
SINK
= 1.5mA
V
CC
= +5.0V, I
SINK
= 4mA
V
CC
= +2.0V, I
SOURCE
= -0.4mA
V
CC
= +5.0V, I
SOURCE
= -1mA
1.8
4.5
15
0.4
0.4
pF
V
V
V
IH
V
IL
I
IL
V
CC
= +2V
V
CC
= +5V
V
CC
= +2V
V
CC
= +5V
V
IN
= 0 to V
CC
-10
10
1.4
2.2
0.6
0.8
10
V
V
nA
pF
0.4
0.8
1.3
CONDITIONS
MIN
2
TYP
MAX
5.5
0.3
1.1
1.05
2.1
4.2
µA
UNITS
V
mA
2
_______________________________________________________________________________________
SPI-Compatible RTC in a TDFN
AC ELECTRICAL CHARACTERISTICS
(V
CC
= +2.0V to +5.5V, T
A
= -40°C to +85°C. Typical values are at V
CC
= +3.3V, T
A
= +25°C, unless otherwise noted.) (Figure 5,
Notes 1, 4)
PARAMETER
OSCILLATOR
X1 to Ground
Capacitance
X2 to Ground
Capacitance
SPI SERIAL TIMING
Maximum Input Rise
Time
Maximum Input Fall
Time
Output Rise Time
Output Fall Time
SCLK Period
SCLK High Time
SCLK Low Time
SCLK Fall to DOUT
Valid
DIN to SCLK Setup
Time
DIN to SCLK Hold
Time
SCLK Rise to
CS
Rise Hold Time
CS
High Pulse Width
CS
High to DOUT
High Impedance
CS
to SCLK Setup
Time
t
rIN
t
fIN
t
rOUT
t
fOUT
t
CP
t
CH
t
CL
t
DO
t
DS
t
DH
t
CSH
t
CSW
t
CSZ
t
CSS
100
C
LOAD
= 100pF
100
2
2
200
100
DIN, SCLK,
CS
DIN, SCLK,
CS
DOUT, C
LOAD
= 100pF
DOUT, C
LOAD
= 100pF
V
CC
= +2V
V
CC
= +5V
1000
238
100
100
100
2
2
10
10
μs
μs
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX6902
25
25
pF
pF
Note 1:
All parameters are 100% tested at T
A
= +25°C. Limits over temperature are guaranteed by design and characterization and
not production tested.
Note 2:
I
CC
is specified with DOUT open,
CS
= DIN = GND, SCLK = 4MHz at V
CC
= +5V; SCLK = 1MHz at V
CC
= +2.0V.
Note 3:
Timekeeping current is specified with
CS
= V
CC
, SCLK = DIN = GND, DOUT = 100kΩ to GND.
Note 4:
All values referred to V
IH
min and V
IL
max levels.
_______________________________________________________________________________________
3
SPI-Compatible RTC in a TDFN
MAX6902
Typical Operating Characteristic
(T
A
= +25°C, unless otherwise noted.)
TIMEKEEPING CURRENT
vs. SUPPLY VOLTAGE
MAX6902 toc01
Detailed Description
The MAX6902 is a real-time clock/calendar with an SPI-
compatible interface and 31 x 8 bits of SRAM. It pro-
vides seconds, minutes, hours, day of the week, date of
the month, month, and year information, held in seven 8-
bit timekeeping registers (Functional
Diagram).
An on-
chip 32.768kHz oscillator circuit requires only a single
external crystal to operate. Table 1 specifies the para-
meters for the external crystal, and Figure 1 shows a
functional schematic of the oscillator circuit. The
MAX6902’s register addresses and definitions are
described in Figure 2 and in Table 2. Time and calendar
data are stored in the registers in binary-coded decimal
(BCD) format. A polled alarm function is included for
scheduled timing of user-defined times or intervals.
10.0
SUPPLY CURRENT (μA)
1.0
0.1
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
Table 1. Acceptable Quartz Crystal
Parameters
PARAMETER
SYMBOL
f
MIN
TYP
32.768
MAX
UNITS
kHz
Frequency
Equivalent
Series
Resistance
(ESR)
Parallel Load
Capacitance
Q Factor
Pin Description
PIN
1
2
3
4
5
6
7
8
NAME
SCLK
DOUT
DIN
GND
CS
V
CC
X2
X1
FUNCTION
Serial Clock Input. SPI clock for DIN and
DOUT data transfers.
SPI Data Output
SPI Data Input
Ground
Chip Select Input. Active low for valid data
transfers.
Power-Supply Pin. Bypass V
CC
to GND
with a 0.1µF capacitor.
External 32.768kHz Crystal
External 32.768kHz Crystal
Exposed Paddle. Internally connected to
GND. Connect to GND, but do not use as
the sole ground connection point or leave
unconnected.
R
S
40
60
kΩ
C
L
Q
11.2
40,000
12.5
13.7
60,000
pF
MAX6902
—
EP
25pF
25pF
X1
EXTERNAL
CRYSTAL
X2
Figure 1. Crystal Oscillator Circuit Schematic
4
_______________________________________________________________________________________
SPI-Compatible RTC in a TDFN
MAX6902
REGISTER ADDRESS
FUNCTION
CLOCK
SECONDS
RD
0
/W
MINUTES
RD
0
/W
HOURS
RD
0
/W
0
0
0
1
0
1
0
0
0
0
1
1
0
0
0
0
0
1
00-59
*POR STATE
00-59
*POR STATE
00-23
01-12
*POR STATE
01-28/29
01-30
0-31
*POR STATE
0
0
1
0
0
1
01-12
*POR STATE
0
0
1
0
1
1
01-07
*POR STATE
0
0
1
1
0
1
00-99
*POR STATE
0
0
1
1
1
1
*POR STATE
0
1
0
0
1
1
00-99
*POR STATE
0
0
WP
0
0
0
ALM
OUT
0
12/24
0
1/0
0
0
0
0
10 SEC
0
0
0
1 SEC
0
0
0
A7 A6 A5 A4 A3 A2 A1 A0
VALUE
D7
REGISTER DEFINITION
D6 D5 D4
D3
D2 D1
D0
10 MIN
0
0
0
1 MIN
0
0
0
10
HR 10
A/P HR
0/1
0
0
0
1 HR
0
0
0
DATE
RD
0
/W
0
0
0
1
1
1
0
0
0
0
0
0
0 10 DATE
0
0
0
0
0
0
0
0
1 DATE
0
0
1
MONTH
RD
0
/W
0 10M
0
0
0
0
0
0
0
0
0
1 MONTH
0
0
1
DAY
RD
0
/W
WEEK DAY
0
0
1
YEAR
RD
0
/W
10 YEAR
1
0
0
1
0
0
1
0
0
0
0
0
1 YEAR
0
0
0
0
0
0
0
0
0
CONTROL
RD
0
/W
CENTURY
RD
0
/W
1000 YEAR
0
0
1
1
100 YEAR
0
0
1
Note: *POR STATE
defines power-on reset state of register contents.
Figure 2. Register Address Definition (Sheet 1 of 3)
_______________________________________________________________________________________
5
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