L6713A Datasheet, PDF (47/64 Pages) Holtek Semiconductor Inc – 2/3 Phase controller with embedded drivers for Intel VR10, VR11 and AMD 6 bit CPUs

L6713A
Output voltage monitor and protections
17 Output voltage monitor and protections
L6713A monitors through pin VSEN the regulated voltage in order to manage the OVP, UVP
and PGOOD (when applicable) conditions. The device shows different thresholds when
programming different operation mode (Intel or AMD, See Table 11) but the behavior in
response to a protection event is still the same as described below.
When using OFFSET funcionality the OVP, UVP and PGOOD thresholds change in according to
the OFFSET voltage:
V_SEN = V_OUT – (R_OFFSET) ⋅ (I_OFFSET) ⇒V_OUT[TH] = V_SEN[TH] + (R_OFFSET) ⋅ I_OFFSET
Protections are active also during soft-start (See “Soft start” Section) while are masked
during D-VID transitions with an additional 32 clock cycle delay after the transition has
finished to avoid false triggering.
17.1
Under voltage
If the output voltage monitored by VSEN drops more than -750mV below the programmed
reference for more than one clock period, L6713A turns OFF all MOSFETs and latches the
condition: to recover it is required to cycle Vcc or the OUTEN pin. This is independent of the
selected operative mode.
17.2
Preliminary over voltage
To provide a protection while VCC is below the UVLO_VCC threshold is fundamental to avoid
damage to the CPU in case of failed HS MOSFETs. In fact, since the device is supplied from
the 12V bus, it is basically “blind” for any voltage below the turn-ON threshold (UVLO_VCC). In
order to give full protection to the load, a preliminary-OVP protection is provided while VCC
is within UVLO_VCC and UVLO_OVP.
This protection turns-ON the low side MOSFETs as long as the VSEN pin voltage is greater
than 1.800V with a 350mV hysteresis. When set, the protection drives the LS MOSFET with
a gate-to-source voltage depending on the voltage applied to VCCDRx and independently
by the turn-ON threshold across these pins (UVLO_VCCDR). This protection depends also on
the OUTEN pin status as detailed in Figure 22.
A simple way to provide protection to the output in all conditions when the device is OFF
(then avoiding the unprotected red region in Figure 22-Left) consists in supplying the
controller through the 5V_SB bus as shown in Figure 22-Right: 5V_SB is always present before
+12V and, in case of HS short, the LS MOSFET is driven with 5V assuring a reliable
protection of the load. Preliminary OVP is always active before UVLO_VCC for both Intel and
AMD Modes.
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