MAX6902ETA+T Maxim Integrated Products, MAX6902ETA+T Datasheet - Page 15

• Manufacturer Part Number: MAX6902ETA+T
• Description: IC RTC SPI COMPAT 8-TDFN
• Manufacturer: Maxim Integrated Products
• Type: Clock/Calendar/NVSRAMr

Specifications of MAX6902ETA+T

• Memory Size: 31B
• Time Format: HH:MM:SS (12/24 hr)
• Date Format: YY-MM-DD-dd
• Interface: SPI, 3-Wire Serial
• Voltage - Supply: 2 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-TDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: MAX6902ETA+TTR

When DOUT is high impedance (CS = high or during a
DIN transfer segment), there is a potential for increased
timekeeping current (up to 100x) if DOUT is allowed to
float. If minimum timekeeping current is desired, then
ensure DOUT is not allowed to float. The microcon-
troller port pin attached to DOUT could be configured
as an input with a weak pullup. An alternate solution is
to use a 100kΩ, or less, pulldown or pullup resistor (for
microcontroller port pins with ≤1µA input leakage).
The MAX6902 contains an integral POR circuit that
ensures all registers are reset to a known state on
power-up. Once V
circuit releases the registers for normal operation. When
V
all register contents to the POR defaults (Figure 2).
Address/Command 17h is reserved for factory testing
ONLY. Do not write to this register. If inadvertent writes
are done to this register, cycle power to the MAX6902.
For most applications, a 0.1µF capacitor from V
GND provides adequate bypassing for the MAX6902. A
series resistor can be added to the supply line for oper-
ation in extremely harsh or noisy environments.
CC
drops to less than 1.6V (typ), the MAX6902 resets
Power-Supply Considerations
______________________________________________________________________________________
CC
rises above 1.6V (typ), the POR
Timekeeping Current
RESERVED Register
Power-On Reset
SPI-Compatible RTC in a TDFN
CC
to
The MAX6902 uses a very-low-current oscillator to mini-
mize supply current. This causes the oscillator pins, X1
and X2, to be relatively high impedance. Exercise care
to prevent unwanted noise pickup.
Connect the 32.768kHz crystal directly across X1 and X2
of the MAX6902. To eliminate unwanted noise pickup,
design the PCB using these guidelines (Figure 7):
1) Place the crystal as close to X1 and X2 as possible
2) Place a guard ring around the crystal, X1 and X2
3) Finally, an additional local ground plane can be
4) Restrict the plane to be no larger than the perimeter of
TRANSISTOR COUNT: 26,418
PROCESS: CMOS
and keep the trace lengths short.
traces (where applicable), and connect the guard
ring to GND; keep all signal traces away from
beneath the crystal, X1, and X2.
added under the crystal on an adjacent PCB layer.
The plane should be isolated from the regular PCB
ground plane, and tied to ground at the MAX6902
ground pin.
the guard ring. Do not allow this ground plane to con-
tribute significant capacitance between X1 and X2.
Chip Information
PCB Considerations
15