L6713A Datasheet, PDF (49/64 Pages) Holtek Semiconductor Inc – 2/3 Phase controller with embedded drivers for Intel VR10, VR11 and AMD 6 bit CPUs

L6713A
18 Over current protection
Over current protection
The device limits the total delivered current turning OFF all the MOSFETs as soon as the
delivery current is higher than an adjustable thresholds.This condition is lathed and power
supply or OUTEN pin cycling is required to restart operations.
The device sources a copy of I_DROOP current from the OCSET pin: connecting a resistor
R_OCP between OCSET pin and SGND the voltage at the OCSET pin depends on the total
delivery output current, as shown in the following relationships:
V_OCSET = R_OCP ⋅
I_DROOP = R_OCP ⋅
D_-----C_-----R_---
R_G
⋅
I_OUT
Figure 23. OCP Connections (left) and waveforms (right).
VOUT
OCP
COMPARATOR
I_DROOP
OCSET
V_OCTH=1.240V
R_OCP
C_OCP
OCSET
UGATE
LGATE
As soon as the OCSET pin voltage is higher than the internal fixed thresholds V_OCTH (1.24V
TYP, See Table 4), the device turns OFF all the MOSFETs and latches the condition.
The OCP threshold can be easily programmed through the R_OCP resistor:
R_OCP
=
---^R-----^G-----
DCR
⋅
-----^V----^O----^C----^T---^H------
I_OUT(OCP)
The Output Over Current threshold has to be programmed, by designing the R_OCP resistors,
to a safe value, in order to be sure that the device doesn't enter OCP during normal
operation of the device. This value must take into consideration also the extra current
needed during the Dynamic VID Transition I_D-VID and, since the device reads across
inductor DCR, the process spread and temperature variations of these sensing elements.
Moreover, since also the internal threshold spreads, the R_OCP design has to consider the
minimum value V_OCTH(min) of the threshold as follow:
R_OCP = _D-----_C-----_R--^R---₍-^G-_m-----_a----_x---₎- ⋅
V_{-----O----C---T----H---}(_---m_-----i_--n_----)
I_OUT(OCP)
where I_OUT(OCP) is the total delivery current for the Over Current condition and it must be
calculated considering the maximum delivery current and I_D-VID (when D-VID are
implemented):
I_OUT(OCP)
>
I_O
U
MAX
T
+
I_D–VID
When it is necessary, filter OCSET pin to introduce a small delay in the Over Current
intervention.
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