AN3064

Using the STC3100

Doc ID 16263 Rev 1

3/15

Figure 2.

ROSC connection for internal or external timebase

The STC3100 automatically recognizes the presence of the external clock signal and uses it

if present. The internal oscillator, however, can be inhibited to force the use of an external

signal by setting the SEL_EXT_CLK bit in the REG_MODE register.

1.3

STC3100 external components

The Rcg resistor is used to sense the current flowing into or from the battery. The value of

the Rcg resistor must be selected based on the maximum peak current in the application;

the voltage drop across the Rcg resistor must not exceed +/-80 mV.

Rcg resistance (Ohm) <= 0.08/peak current (A).

For instance, a current of up to +/- 2 A can be monitored using a 33 m

Ω resistor.

The STC3100 has separate pins for the power supply (VCC) and voltage measurement

(VIN) inputs, providing an easy way of implementing an input filter or additional ESD

protection without affecting the accuracy of the voltage measurement.

Figure 3.

STC3100 connections with VIN input filter and additional ESD protection

C1 is the normal recommended decoupling capacitor (1 µF).

R1 and D1 provide additional ESD protection to the STC3100’s VCC pin. A typical value for

R1 is 150

Ω and D1 is a 5.6 V Zener diode.

R2 provides additional ESD protection to the STC3100’s VIN pin. A typical value for R2 is

1 k

Ω.. The input impedance of the VIN pin is approximately 500 kΩ; an R2 resistor value of

1 k

Ω will not affect the accuracy of the battery voltage measurement. The VIN input must be

connected directly (through the R2 resistor) to the battery’s positive terminal.

AM04579

ROSC

STC3100

ROSC

STC3100

32,768 Hz RTC

200 k

Ω, 0.1%

AM04580

VCC

VIN

CG

STC3100

Battery

Rcg

R1

R2

C1

C2

D1

GND

Gnd

System supply