TDA4916GG Datasheet, PDF (26/30 Pages) Siemens Semiconductor Group – SMPS-IC with MOSFET Driver Output

TDA 4916 GG
Instructions for the Approximate Calculation of the Maximum Duty Cycle of the FG
when R_VS or R_GND is Connected to Input C_T.
1. General remarks
Duty cycle ν = ON time/period
Time t = C_T ∆V_CT/I_CT
∆V_CT = approx. 0.6 V
Current I_RGND = 2.2 V/R_GND
Current I_RT = 2.5 V/R_T
Current I_RVS = (12 V − 2.2 V)/R_VS
Mean value V_{CT Mean} = approx. 2.2 V
To facilitate better general understanding, the equations are not abbreviated in the
following.
The wanted quantity can be isolated using the rules of arithmetic.
2. Calculation for connection of R_VS (ν > 0.5)
-^C-----^T-----^â‹----⁰---^.--⁶------^V---
ν_max
=
--------------------^I--^R----^T-----^–-----^I--^R-----^V----^S--------------------
-^C-----^T-----^â‹----⁰---^.--⁶------^V--- + -^C------^T----^â‹----⁰----^.--⁶-----^V----
I_RT – I_RVS I_RT + I_RVS
3. Calculation for connection of R_GND (ν < 0.5)
ν_max
=
-----------------------^I-----^{R--C------T----T------+----⋅-------0}-^I-----R--^.---^6---G---------^{VN--------D---------------------------}
I^---_R^-C---_T^--T---+^{--⋅----0}I^---_R^-.-6--_G^----V_N^----_D^{--- +} I^---_R^-C---_T^--T---–^--⋅---I^-0--_R^-.--6-_G^-----V_N^----_D^--
Version 2.0
26
1 May 1996