Functions, pins and components description

TDA7570

12/17

4

Functions, pins and components description

4.1

Components with critical placement and type:

●

Ci-L1, Ci-L2, Ci-R1, Ci-R2 must be placed as near as possible to the sources of the

respective power MOS. If 2 power MOS in parallel are needed, can be useful to place a

couple of capacitors for each couple of power MOS. These capacitors are needed to

absorb the high di/dt current present during the Pchannel/Nchannel and

Nchannel/Pchannel transition that can cause high peak voltages on the power supply

wiring connection due to their parasitic inductance.

●

The capacitors placed between +Vs to GND and to -Vs are distributed along the power

lines. With P.C. board with very short connections, some of these capacitors can be

avoided (Cvs-1, Cvs-2, Cd3, Cd4, Cd5, Cd6).

●

The current sensing resistors Rsens-N-L, Rsens-P-L, Rsens-P-R and Rsens-N-R must

be not inductive components, as example, made by a costant an wire.

4.2

Input capacitors

●

The value of the input capacitors (Cin-L+, Cin-L-, Cin-R+, Cin-R- depends on the

desired -3dB high pass cutoff frequency, following the formula:

4.3

Short circuit protection current calculation

Figure 4.

Short circuit protection current diagram (example for the N-channel)

← if Rp2 is not used

F3dB

()

1

6.28 10000 C

in

⋅⋅

----------------------------------------------

=

Cfil (typ 2.2nF)

to -Vs

Rsens

(not inductive resistor)

Typ. Values = 10 – 30 mOhm

Rfil (typ. 100 Ohm)

Rp1 (typ=4.7kOhm)

Rp2

Vfil = Ispx1 x Rfil = 20mV Typ

SPx1 pin

SPx2 pin

TDA7570

Vp=100mV Typ

comparator

Imos

I

lim

1

Rsens

------------------ Vpx

Rp1

Rp2

+

()

⋅

Rp2

--------------------------------------------------

Vfil

+

⎝⎠

⎛⎞

=

I

lim

1

Rsens

------------------ Vpx

Vfil

+

()

=