DS1343_1112 Datasheet, PDF (15/20 Pages) Maxim Integrated Products – Low-Current SPI/3-Wire RTCs

Low-Current SPI/3-Wire RTCs
R1
1kΩ
VCC
R2
VBAT
2kΩ
R3
4kΩ
1 0F 18 SELECT
NOTE: ONLY 1010 CODE ENABLES CHARGER
1 OF 2
SELECT
1 OF 3
SELECT
TRICKLE
CHARGER TCS
TCS
TCS
TCS
DS
DS
RS
RS
REGISTER
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
TCS = TRICKLE-CHARGER SELECT
DS = DIODE SELECT
RS = RESISTOR SELECT
Figure 2. Trickle Charger Block Diagram
Table 3. Trickle-Charger Resistor and Diode Select
TCS3
TCS2
TCS1
TCS0
DS1
DS0
RS1
RS0
FUNCTION
X
X
X
X
X
X
0
0
Disabled
X
X
X
X
0
0
X
X
Disabled
X
X
X
X
1
1
X
X
Disabled
1
0
1
0
0
1
0
1
No diode, 1kI
1
0
1
0
0
1
1
0
No diode, 2kI
1
0
1
0
0
1
1
1
No diode, 4kI
1
0
1
0
1
0
0
1
One diode, 1kI
1
0
1
0
1
0
1
0
One diode, 2kI
1
0
1
0
1
0
1
1
One diode, 4kI
0
0
0
0
0
0
0
0
Initial power-on state—disabled
X = Don’t care.
Assume, for the purposes of the example, that a system
power supply of 5V is applied to VCC and a super cap is
connected to VBAT. Also assume that the trickle charger
has been enabled with one diode and resistor R1. The
maximum current IMAX would be calculated as follows:
IMAX = (5.0V - diode drop)/R1 ≈ (5.0V - 0.6V)/2kΩ ≈
2.2mA
As the super cap charges, the voltage drop between
VCC and VBAT decreases, and therefore, the charge
current decreases.
Serial Port Operation
The devices offer the flexibility to choose between two
serial-interface modes. The component can commu-
nicate with the SPI interface or with a standard 3-wire
interface. The interface method used is determined by
SERMODE. When SERMODE is connected to VCC, SPI
communication is selected. When SERMODE is con-
nected to ground, standard 3-wire communication is
selected.
15