Micro Crystal
Development Board
RV-1805-C3
RV-1805-C3
The RV-1805-C3 is soldered onto the Development Board.
Every pin is either accessible at test pins 1 – 10 or at the test vias situated around the device.
The following passive components are already soldered on the Board:
C1
xx
Option for Supercap for backup supply
C2
10 nF
Backup supply buffer cap
C2
xx
Option for double layer cap for backup supply
C5
47pF
Filter cap for auto calibration
C6
10 nF
Decoupling capacitor between V
SS
and V
DD
R1
0Ω
to limit inrush current for external Supercap
R2
10 kΩ
Pull-up resistor INT to V
DD
R3
10 kΩ
Pull-up resistor SCL to V
DD
R4
10 kΩ
Pull-up resistor SDA to V
DD
R5
10 kΩ
Pull-up resistor PSW to V
DD
R6
100 kΩ
Pull-up resistor WDI to V
DD
R7
10 kΩ
Pull-up resistor RST to V
DD
R8
330 Ω
Current limiting resistor for LED
LED green
Supply current consumption of the LED has to be considered
DEVELOPMENT BOARD
JUMPER 1
Power for LED
JUMPER 2
Add Supercap
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Micro Crystal
Development Board
SCHEMATICS
RV-1805-C3
PINOUT RV-1805-C3
# 1
# 2
# 3
# 4
# 5
V
DD
CAP_RC
CLK / INT
SCL
SDA
# 10
# 9
# 8
# 7
# 6
RST
WDI
PSW
V
BACKUP
V
SS
PIN DESCRIPTION
Symbol
V
DD
Cap_RC
CLK / INT
SCL
SDA
V
SS
V
BACKUP
PSW
WDI
RST
Pin #
1
2
3
4
5
6
7
8
9
10
Description
Positive supply voltage, primary power connection
Auto calibration filter connection. A 47 pF ceramic capacitor should be placed between this pin and VSS for
improved Auto calibration mode timing accuracy.
Clock output / Interrupt. Primary interrupt output connection. It is an open drain output. An external pull-up
resistor must be added to this pin. It should be connected to the host device and is used to indicate when the
RTC can be accessed via the I
2
C-bus interface
I
2
C Serial Clock Line input. A pull-up resistor is required on this pin
I
2
C Serial Data Line. A pull-up resistor is required on this pin
Ground connection
Backup supply voltage
Power Switch output. Secondary interrupt output connection. It is an open drain output
Watchdog timer reset Input connection. It may also be used to generate an External interrupt
Reset output. It is an open drain output
Datasheet and Application-Manual are available for download under:
www.microcrystal.com
3/4
Micro Crystal
Development Board
RTC set-up for lowest power consumption
RV-1805-C3
Upon initial power-up the Real-time Clock module RV-1805-C3 has activated some outputs. These are pulling
additional power. They need to be switched off first! The key points in Hardware and Software are outlined to
achieve the exceptionally low current consumption of << 100nA.
(Reference:
Application Note
RV-1805-C3 Measuring Current Consumption and Frequency Accuracy)
Hardware:
To measure current draw of the RV-1805-C3, an A-meter must be inserted in series with the RV-1805-C3 VDD
1. Demoboard RV-1805-C3
2. Current measured into VDD (at pin 1)
3. Disconnect jumper J1 to switch off the LED (5mA), refer to the picture below
4. Replace jumper J2 by an nA-meter, connect a Li battery 3V to ground
2
5. Connect the Demoboard with: VSS, SCL, SDA, VDD with µA-meter, e.g. with the USB-I C-Bus dongle
2
6. Power up the device: VSS, VDD and connect the I C-Bus SCL, SDA
Software:
Steps for setting the RTC in the lowest power mode:
1. The nRST and PSW outputs are active low and draw pulldown currents. (Total about 650µA)
2. Deactivate these outputs in Control register1:
- CLKB must be set to 1
- PSWB needs to be set 1, for this LKP bit must be cleared first!
If only either bit CLKB or PSWB is set to 1, the current is reduced only to some 320µA
4. Control register 2: all bits set to 0, making sure no other modes are activated
5. The program sequence for setting the RTC RV-1805-C3 into low power mode can be implemented in a
2
few lines of code:
START condition I C-Bus
D2h Slave address: write
1Dh Address pointer
00h Set LKP = 0
2
STOP condition I C-Bus
START
D2h Slave address: write
10h Address pointer to control register 1
30h Set PSWB and CLKB bits =1
00h Clear control register 2
STOP
6. Current draw into VDD is now some 3.7µA, 3.6µA derive from leakage currents through I/Os
Hardware: Switch to back-up mode:
7. Power down the interface: VDD, SCL, SDA = 0V. Read the current into VBACKUP on the nA-meter:
<0.10 µA
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