ISL62882HRTZ Intersil, ISL62882HRTZ Datasheet - Page 20

• Manufacturer Part Number: ISL62882HRTZ
• Description: IC REG PWM 2PHASE BUCK 40TQFN
• Manufacturer: Intersil

Specifications of ISL62882HRTZ

• Applications: Controller, Intel IMVP-6.5™
• Voltage - Input: 5 V ~ 25 V
• Number Of Outputs: 1
• Voltage - Output: 0.0125 V ~ 1.5 V
• Operating Temperature: -10°C ~ 100°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Current Monitor
The ISL62882 provides the current monitor function. The
IMON pin outputs a high-speed analog current source
that is 3 times of the droop current flowing out of the FB
pin. Thus Equation 13:
As Figures 1 and 2 show, a resistor R
the IMON pin to convert the IMON pin current to voltage.
A capacitor can be paralleled with R
voltage information. The IMVP-6.5™ specification
requires that the IMON voltage information be referenced
to VSS
The IMON pin voltage range is 0V to 1.1V. A clamp circuit
prevents the IMON pin voltage from going above 1.1V.
FB2 Function
The FB2 function is only available when the ISL62882 is
in 2-phase configuration.
Figure 16 shows the FB2 function. A switch (called FB2
switch) turns on to short the FB and the FB2 pins when
the controller is in 2-phase mode. Capacitors C3.1 and
C3.2 are in parallel, serving as part of the compensator.
When the controller enters 1-phase mode, the FB2
switch turns off, removing C3.2 and leaving only C3.1 in
the compensator. The compensator gain will increase
with the removal of C3.2. By properly sizing C3.1 and
C3.2, the compensator cab be optimal for both 2-phase
mode and 1-phase mode.
When the FB2 switch is off, C3.2 is disconnected from the
FB pin. However, the controller still actively drives the
FB2 pin voltage to follow the FB pin voltage such that
C3.2 voltage always follows C3.1 voltage. When the
controller turns on the FB2 switch, C3.2 will be
reconnected to the compensator smoothly.
The FB2 function ensures excellent transient response in
both 2-phase mode and 1-phase mode. If one decides
not to use the FB2 function, simply populate C3.1 only.
Adaptive Body Diode Conduction Time
Reduction
In DCM, the controller turns off the low-side MOSFET
when the inductor current approaches zero. During on-
time of the low-side MOSFET, phase voltage is negative
and the amount is the MOSFET r
which is proportional to the inductor current. A phase
comparator inside the controller monitors the phase
voltage during on-time of the low-side MOSFET and
I
IMON
VSEN
CONTROLLER IN
2-PHASE MODE
FIGURE 16. FB2 FUNCTION IN 2-PHASE MODE
=
SENSE
C2
3
R1
×
R3
I
droop
.
VREF
FB2
FB
C1
C3.1
C3.2
E/A
R2
COMP
20
VSEN
CONTROLLER IN
1-PHASE MODE
DS(ON)
C2
imon
R1
imon
R3
voltage drop,
to filter the
VREF
is connected to
FB2
FB
ISL62882, ISL62882B
C1
C3.1
C3.2
E/A
R2
(EQ. 13)
COMP
compares it with a threshold to determine the
zero-crossing point of the inductor current. If the
inductor current has not reached zero when the low-side
MOSFET turns off, it’ll flow through the low-side MOSFET
body diode, causing the phase node to have a larger
voltage drop until it decays to zero. If the inductor
current has crossed zero and reversed the direction when
the low-side MOSFET turns off, it’ll flow through the high-
side MOSFET body diode, causing the phase node to
have a spike until it decays to zero. The controller
continues monitoring the phase voltage after turning off
the low-side MOSFET and adjusts the phase comparator
threshold voltage accordingly in iterative steps such that
the low-side MOSFET body diode conducts for
approximately 40ns to minimize the body diode-related
loss.
Overshoot Reduction Function
The ISL62882 has an optional overshoot reduction
function. Tables 2 and 4 show to enable and disable it.
When a load release occurs, the energy stored in the
inductors will dump to the output capacitor, causing
output voltage overshoot. The inductor current
freewheels through the low-side MOSFET during this
period of time. The overshoot reduction function turns off
the low-side MOSFET during the output voltage
overshoot, forcing the inductor current to freewheel
through the low-side MOSFET body diode. Since the body
diode voltage drop is much higher than MOSFET R
voltage drop, more energy is dissipated on the low-side
MOSFET therefore the output voltage overshoot is lower.
If the overshoot reduction function is enabled, the
ISL62882 monitors the COMP pin voltage to determine
the output voltage overshoot condition. The COMP
voltage will fall and hit the clamp voltage when the
output voltage overshoots. The ISL62882 will turn off
LGATE1 and LGATE2 when COMP is being clamped. All
the low-side MOSFETs in the power stage will be turned
off. When the output voltage has reached its peak and
starts to come down, the COMP voltage starts to rise and
is no longer clamped. The ISL62882 will resume normal
PWM operation.
When PSI# is low, indicating a low power state of the
CPU, the controller will disable the overshoot reduction
function as large magnitude transient event is not
expected and overshoot is not a concern.
While the overshoot reduction function reduces the
output voltage overshoot, energy is dissipated on the
low-side MOSFET, causing additional power loss. The
more frequent transient event, the more power loss
dissipated on the low-side MOSFET. The MOSFET may
face severe thermal stress when transient events
happen at a high repetitive rate. User discretion is
advised when this function is enabled.
FN6890.3
dson