ISL6556ACBZ Intersil, ISL6556ACBZ Datasheet - Page 16

• Manufacturer Part Number: ISL6556ACBZ
• Description: IC CTRLR MULTIPHASE VRM10 28SOIC
• Manufacturer: Intersil

Specifications of ISL6556ACBZ

• Applications: Controller, Intel VR10X
• Voltage - Input: 3 ~ 12 V
• Number Of Outputs: 4
• Voltage - Output: 0.84 ~ 1.6 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Soft-Start
During soft start, the DAC voltage ramps linearly from zero to
the programmed VID level. The PWM signals remain in the
high-impedance state until the controller detects that the
ramping DAC level has reached the output-voltage level.
This protects the system against the large, negative inductor
currents that would otherwise occur when starting with a pre-
existing charge on the output as the controller attempted to
regulate to zero volts at the beginning of the soft-start cycle.
The soft-start time, t
64 switching cycles followed by a linear ramp with a rate
determined by the switching period, 1/f
For example, a regulator with 250kHz switching frequency
having VID set to 1.35V has t
A 100mV offset exists on the remote-sense amplifier at the
beginning of soft start and ramps to zero during the first 640
cycles of soft start (704 cycles following enable). This
prevents the large inrush current that would otherwise occur
should the output voltage start out with a slight negative
bias.
During the first 640 cycles of soft start (704 cycles following
enable) the DAC voltage increments the reference in 25mV
steps. The remainder of soft start sees the DAC ramping
with 12.5mV steps.
Fault Monitoring and Protection
The ISL6556A actively monitors output voltage and current
to detect fault conditions. Fault monitors trigger protective
measures to prevent damage to a microprocessor load. One
common power good indicator is provided for linking to
external system monitors. The schematic in Figure 10
outlines the interaction between the fault monitors and the
power good signal.
t
SS
FIGURE 9. SOFT-START WAVEFORMS WITH AN UN-BIASED
=
64
-----------------------------------------
+
1280 VID
f
SW
OUTPUT. FSW = 500kHz
⋅
SS
, begins with a delay period equal to
2ms/DIV
VOUT, 500mV/DIV
500μs/DIV
16
SS
equal to 6.912ms.
SW
EN, 5V/DIV
.
(EQ. 10)
ISL6556A
Power Good Signal
The power good pin (PGOOD) is an open-drain logic output
that transitions high when the converter is operating after
soft start.
a successful soft start. PGOOD only transitions low when an
undervoltage condition is detected or the controller is
disabled by a reset from EN, ENLL, POR, or one of the
no-CPU VID codes. After an undervoltage event, PGOOD
will return high unless the controller has been disabled.
PGOOD does not automatically transition low upon
detection of an overvoltage condition.
Undervoltage Detection
The undervoltage threshold is set at 75% of the VID code.
When the output voltage at VSEN is below the undervoltage
threshold, PGOOD gets pulled low.
Overvoltage Protection
When VCC is above 1.4V, but otherwise not valid as defined
under Power on Reset in Electrical Specifications, the
overvoltage trip circuit is active using auxiliary circuitry. In
this state, an overvoltage trip occurs if the voltage at VSEN
exceeds 1.8V.
With valid VCC, the overvoltage circuit is sensitive to the
voltage at VDIFF. In this state, the trip level is 1.7V prior to
valid enable conditions being met as described in Enable
and Disable. The only exception to this is when the IC has
been disabled by an overvoltage trip. In that case the
overvoltage trip point is VID plus 200mV. During soft start,
the overvoltage trip level is the higher of 1.7V or VID plus
200mV. Upon successful soft start, the overvoltage trip level
is 200mV above VID. Two actions are taken by the
PGOOD pulls low during shutdown and releases high after
VDIFF
FIGURE 10. POWER GOOD AND PROTECTION CIRCUITRY
REFERENCE
DAC
75%
VID + 0.2V
UV
AND CONTROL LOGIC
+
-
SOFT START, FAULT
OV
EACH CHANNEL
REPEAT FOR
OC
+
-
OC
+
-
100μA
I
1
PGOOD
OVP
100μA
I
AVG