TLE7235E Datasheet, PDF (17/37 Pages) Infineon Technologies AG – 8 Channel High-Side and Low-Side Relay Switch with Limp Home Mode

TLE7235E
Power Stages
6.3
Inductive Output Clamp
When switching off inductive loads with low-side switches, the potential at pin OUT rises to V_DS(CL) potential,
because the inductance intends to continue driving the current. For the high-side channels, the potential at pin
OUT drops below ground potential to V_S(CL). The voltage clamping is necessary to prevent destruction of the
device, see Figure 5 for details. Nevertheless, the maximum allowed load inductance is limited by the max.
clamping energy E_AR see electrical characteristics “E_AR” on Page 10.
V_bb
high side
channel
V_DS(CL)
V_S(CL)
GND
VBB
low side
channel
OUT ^I S
V_S
L,
I_L
R_L
V_DS(CL)
L,
I_{L RL}
OUT ^ID
V_D
GND
Figure 5 Output Clamp Implementation
OutputClamp.emf
Maximum Load Inductance
During demagnetization of inductive loads, energy has to be dissipated in the TLE7235E. This energy can be
calculated with following equations:
E = V_D(CL) ⋅
V_{-----b--b----}–_-----V_{----D----(-C----L--)}
⋅
ln

1
–
--------^R-----^L----^â‹---^I--^L---------


R_L
 ^V_bb ^{– V}_D(CL) 
+ I_L
⋅ --^L----
R_L
Low-side
(1)
E = (V_bb – V_S(CL)) ⋅
V_{-----S---(-C----L--)}
R_L
⋅

ln1

–
-^R----^L----^â‹---^I--^L-
V_S(CL)
+ I_L
⋅ --^L----
R_L
High-side
(2)
These equations simplify under the assumption of R_L = 0:
E
=
1_--
2
LI_L2
⋅

1
–
------------^V----^b---^b------------


 ^V_bb ^{– V}_D(CL) 
Low-side
(3)
E
=
1_--
2
LI_L2
⋅

1
–
----^V----^b---^b----


 ^V_S(CL)
High-side
(4)
The maximum energy, which is converted into heat, is limited by the thermal design of the component.
Data Sheet
17
Rev. 1.0, 2008-10-30