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IDT821621

LONG HAUL SLIC

Integrated Device Technology 

IDT821621

calculated by the equation below:

CCAS

=

--------------1--------------

1.7 • 105πfC

Where, fC is the desired filter cut-off frequency.

IMPEDANCE MATCHING

The two-wire AC input impedance R2WIN is programmed by means

of an external impedance (RT) connected between the RSN and VTX

pins (see Figure 13). RT is calculated by the following equation:

RT = 250(R2WIN – 2RF)

Where, RF is the value of the fuse resistor. Note that when computing

RT, the internal current amplifier pole and any external stray capacitance

between the RSN and VTX pins must be taken into account.

RECEIVE GAIN SETTING

The 4-wire to 2-wire gain (G42L) is defined as the receive gain. It is

calculated by the following equation:

G 42 L

=

---R----L---

RRX

•

--------------------5---0----0---R-----T--------------------

RT + 250(RL + 2RF)

Where, RL is the terminating impedance; RRX is connected between

VRX and RSN; RT is defined above; RF is the fuse resistor. See Figure

11 for details.

LONG HAUL SLIC

THERMAL MANAGEMENT

The IDT821621 uses a power management technique of offloading

the thermal energy from the SLIC to an external resistor RTMG. RTMG is

connected between the TMG and VBAT pins as shown in Figure 13.

This resistor shares some of the loop current and limits the on-chip

power dissipation in Active state.

The selection of RTMG normally needs to satisfy the following

condition: with the programmed loop current being fed into a short circuit

loop from the nominal battery, all of the loop current is supplied by RTMG.

So, RTMG can be calculated by the equation below:

RTMG

≥





--V---B---A---T------–----8---V--

ILOOP

–

70Ω

The power dissipated in the resistor RTMG during Active state is:

PRTMG = (----V----B---A-(--T-R----T–--M---8-G--V--+--–---7--(-0-I--ΩL----•-)--2-R----L--)---)--2- • RTMG

The power dissipated in the SLIC during Active state is:

PSLIC = VBAT • IL – PRTMG – RL(IL)2 + 0.12W

Functional Description

9

October 8, 2003

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