ncp5372 ON Semiconductor, ncp5372 Datasheet - Page 20

• Manufacturer Part Number: ncp5372
• Description: High Efficiency Two-phase Step-down Power Controller For Imvp-6.5 Mobile Cpu Core Power Supplies
• Manufacturer: ON Semiconductor

pass filtered internally to avoid switching noise issues. The current limit threshold voltage is compared to the
total sensed inductor current. An over current condition for about 50us will cause a fault condition and shutdown
the PWM controller. The controller must be reset by cycling VR_ON, VCC, VCCP1, VCCP2, or VIN.
IMVP Power Good Output
Once VR_ON is activated, Vcc_core ramps to about Vboot. Then, the first VID code is captured and a timer
starts to wait for Tboot+Tcpu_up. At the end of the timing, CLK_ENABLE# is set low and Vcc_core is regulated
to a DAC voltage determined by the VID code. When CLK_ENABLE# goes low, another timer starts and waits
for Tcpu_pwrgd,
At the end of the timing, the output voltage will be monitored whether it is within the Power Good Window, about
+200mV/-300mV of the expected voltage. If yes, IMVP_PWRGD is set high. If otherwise, there is a 200us
blanking window to allow for undershoot/overshoot before IMVP_PWRGD is set low. Then, the controller must
be reset by cycling VR_ON, VCC, VCCP1, VCCP2 or VIN.
When the controller is the DCM mode operation, the upper threshold will be disabled.
Severe Over Voltage Protection (Protection against a shorted high side MOSFET)
The output voltage is sensed via VS+ and VS- inputs and is compared to a fixed threshold of 1.55V. If the
output voltage exceeds 1.55V, the severe OVP fault is tripped within 2µs. The high side MOSFETs are shut off
and the low side MOSFETs are turned on to discharge the excess voltage at the output. The low side
MOSFETs will continue to turn on until the output falls below the release threshold of about 0.3V. The controller
will continue monitor for the severe overvoltage condition. If the output voltage rises again and reaches the
1.55V, the low side MOSFETs will turn on again to discharge the over voltage. The low side MOSFETs will
repeatedly switch on and off if the over voltage condition persists. This action provides greatest protection
against severe over voltage fault and avoids the generation of large negative voltage at the output. The severe
OVP fault can be reset by cycling VR_ON, VCC, VCCP1 or VCCP2.
Thermal Shutdown
The thermal shutdown is tripped when the device junction temperature reaches 150°C. When the thermal shutdown is
triggered, the TG, BG, and PWRGD are latched low. The output voltage is then discharged through the 106
MOSFET. The thermal shutdown can be reset and the controller can be re-started again by toggling the VR_ON, VCC,
VCCP1, VCCP2 or VIN after the device junction temperature is dropped by 30°C.
Current Monitor
The controller includes an IMON output voltage which is proportional to the core supply output current. The
IMON proportional gain is external programmable. The IMON reference is internally connected to VS- and the
IMON output can source/sink up to 500uA. Therefore, the current monitor output voltage can be given by the
following equation:
V
V
The IMON output voltage maximum will be clamped at 1.15V.
IMON
IMON
= 900mV at IOUT = Imax,
= 0mV at IOUT = 0A.
Rev0.3
V
IMON
Confidential and Proprietary – Not for Public Release
=
∑
V
(
CS
N
+
,
CS
ON Semiconductor CONFIDENTIAL
N
−
)
×
Mar 19, 2008 - Page 18
6
×
GAIN
DRPAMP
×
GAIN
IMON
(eq. 2)
internal