APW8855 Datasheet, PDF (31/43 Pages) Anpec Electronics Coropration – High Current, High Frequency 7 Outputs Voltage Regulator and Power Management IC for High Performance Tablet and Ultra Notebook Applications

APW8855
15.Function Description
15.1 VR Function Description
Soft-Start
All VRs are equipped soft-start function, when enable signal of each VR is activated, an internal soft start ramps the
output voltage at a rate of 10mV/usec. This allows the output voltage to ramp up gradually, eliminating overshoot and
excessive in rush current.
Over Voltage Protection (OVP) for VR3 and VR4
The over voltage protection circuitry monitors the feedback voltage to prevent the output from accidently exceeding the
desired set point. Once the feedback voltage exceeds typically 130% of the set point voltage, the high side MOSFET
turn off, Low side MOSFET turns off and internal latch circuitry is activated. This insures protection of the load damage
and circuit reset is only achieved either by internal reset via the I2C, CTL or by cycling the power.
Over Current Protection (OCP) and Under Voltage Protection (UVP) for VR3 and VR4
The switching converter is protected against gradual over current or sudden short on its output. When inductor current
peak value exceeds the set threshold an internal over-current protection is activated which turns off the high side and
low side MOSFETs.
Once the output voltage drops below a typical threshold of 70% of the output set point value, both high side and low
side MOSFETs turn off and an internal latch circuit is initiated.
When any of OCP or UVP is activated, the IC will be latch off, need reset via the I2C, CTL or by cycling the power.
Over Voltage Protection (OVP) and Under Voltage Protection (UVP) for VR1, VR2 and VR5
Once the output voltage drops below a typical threshold of 70% of set point value or the output voltage exceeds typically
130% of the set point voltage, the PWM signal will be latched low to turn off the converter and discharge the output
voltage.
When any of UVP or OVP is activated, need reset via CTL or by cycling the power.
Soft-Stop
When VR3 or VR4 is shut down by CTL or I2C, both Upper and Lower MOSFETs will be turned off and an internal
MOSFET with about 10ohm (Typ.) Rds-on discharges the output via the FBP pin. The VR7 also discharges the output
via the output pin.
When VR1, VR2, VR5 is shut down by CTL or I2C, the PWM signal pin will be low level to discharge the output voltage
via the low-side MOSFET of APW8703.
VDD_FCH_S5 Output Voltage
The VDD_FCH_S5 output voltage level will be changed between internal fixed LDO regulator and external REFIN input
voltage, and it depends on S5_MUX signal and the REFIN voltage level. When MUX_S5 is high, the FCH_S5 output
voltage will follow the REFIN input voltage. When MUX_S5 is low, REFIN input voltage is below 0.78mV, FCH_S5
output voltage will change to internal LDO regulator. When MUX_S5 is low, and REFIN input voltage is above 0.78mV,
FCH_S5 output voltage will follow the REFIN input voltage. Below table shows the FCH_S5 output voltage operation.
MUX_S5
H
L
L
REFIN
X
<0.78V
≧0.78V
VDD_FCH_S5 Output
Track REFIN Voltage
Internal LDO regulator Output
Track REFIN Voltage
Copyright © ANPEC Electronics Corp.
31
Rev. A.1 - Dec., 2015
www.anpec.com.tw