LTC3335 datasheet(2/22 Pages) LINER

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dc2343afb

DEMO MANUAL DC2343A

operating principle

The demo board is pictured in Figure 2a and Figure 2b,

with schematics shown in Figure 18 and Figure 19. The

provided USB cable connects the demo board to the PC.

With Linear Technology’s QuikEval™ program running in

the background of the PC, a five windowed GUI, pictured

in Figure 6 will pop up.

The GUI sends high level commands to the onboard

microcontroller via the USB interface. The GUI receives

the raw LTC3335 register values and converts them into

application values, which are easily understood by the

user. The GUI also writes to the internal registers to set the

accumulator value and the accumulator alarm threshold.

The board is shipped with a peak buck-boost inductor

current of 100mA and an output voltage setting of 3.3V.

The board is configurable via jumpers to set the output

voltage between 1.8V and 5V. Using a soldering iron to

change the location of some 0Ω resistors and a different

value inductor for the buck-boost converter, the board

can be modified to accommodate 5mA to 250mA peak

inductor current settings. This flexibility is very helpful

when working with higher-impedance batteries such as

the Tadiran primary lithium-thionyl chloride (Li-SOCl2)

long life batteries.

The demo board can be controlled by the GUI or by

an external processor. When the jumper assembly on

JP5 is in the B-C location the internal processor is con-

nected to the LTC3335 device and the GUI is able to

monitor the status of the registers. The B-C location is

the default for the DC2343A, as the PIC16 may consume

current if left connected to the LTC3335 without the

USB cable attached. When the jumper assembly on JP5

is moved to the A-B location, the onboard processor is

disconnectedfromtheLTC3335.Wheninthislocationrow

C pins can be used to control and monitor the LTC3335

via an external processor.

The measurement of the VBAT and the VOUT voltages is

done with a sampled ADC reading to minimize power

dissipation and maintain the available accuracy from the

processor ADC. Refer to page two of the schematic and

the VBAT voltage measurement components for the fol-

lowing discussion. Resistor R18 and capacitor C11 form

a 1.6kHz low-pass filter to remove the high frequency

switching noise from the VBAT measurement. M1 is a

combination of a PFET and NFET configured with the

PFET as a pass device and the NFET along with resistor

R24 performing the function of a level translator to turn

on and off the PFET with the GN1 signal. This allows the

use of relatively low valued resistors (R25 and R26) as

the divider resistors into the ADC. The divider resistors

are needed to keep the input signal within the input range

of the ADC (0V to 4.096V). For the processor used on the

board the, input resistance to the ADC is recommended

to be less than or equal to 10kΩ. Both voltage sampling

circuits (VBAT and VOUT) are controlled by the same signal.

At a 3 second sampling rate, the PFETs are turned on for

120µs to perform the ADC conversions. Performing both

conversionswithin120µsevery3secondscanaddasmuch

as 35nA to the input current under worst-case conditions

when the battery is at 1.8V and the output voltage is set

to 5V. Under normal operation where the battery is 3.6V

and the output voltage is 3.3V, the voltage sampling adds

approximately 15nA to the input current.

For a more details about the operation of the LTC3335 IC

please, refer to the LTC3335 data sheet.

Connecting a DC9003A-B Dust Mote

WhenconnectingaDC9003A-BDustmotetotheDC2343A

demo board, two resistors in the Dust mote must be

changedforthemotetoswitchoverfromthebatterypower

to the output of the LTC3335, when PGOOD goes high.

Change resistor R3 to 750kΩ and change R4 to 5.1MΩ,

on the Dust mote demo board. In addition, connect J3

Pin 3 to E6 (GND).

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