isl62883c Intersil Corporation, isl62883c Datasheet - Page 22
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isl62883c
Manufacturer Part Number
isl62883c
Description
Multiphase Pwm Regulator For Imvp-6.5? Mobile Cpus And Gpus
Manufacturer
Intersil Corporation
Datasheet
1.ISL62883C.pdf
(43 pages)
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Overcurrent
Way-Overcurrent
(2.5xOC)
Overvoltage
+200mV
Undervoltage -
300mV
Phase Current
Unbalance
Overvoltage 1.55V
Over-Temperature
Current Monitor
The ISL62883C 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 18:
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 ISL62883C 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
I
IMON
VSEN
CONTROLLER IN
2-PHASE MODE
FAULT TYPE
=
SENSE
TABLE 5. FAULT PROTECTION SUMMARY
C2
3
R1
×
R3
I
droop
.
FIGURE 16. FB2 FUNCTION
VREF
FB2
FB
C1
C3.1
C3.2
PROTECTION
Immediately Low-side
DURATION
E/A
R2
BEFORE
FAULT
120µs
<2µs
1ms
COMP
22
VSEN
CONTROLLER IN
1-PHASE MODE
PROTECTION
PWM tri-state,
PGOOD
latched low
MOSFET on
until
<0.85V, then
PWM tri-state,
PGOOD
latched low.
1ms
C2
imon
ACTION
R1
imon
R3
Vcore
to filter the
VREF
is connected to
FB2
FB
C1
C3.1
C3.2
E/A
R2
VR_ON
toggle or
VDD
toggle
VDD
toggle
N/A
FAULT
RESET
(EQ. 18)
ISL62883C
COMP
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
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 ISL62883C has an optional overshoot reduction
function. Tables 2 and 4 show how 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
ISL62883C monitors the COMP pin voltage to determine
the output voltage overshoot condition. The COMP
voltage will fall and hit the clamp voltage when the
DS(ON)
voltage drop,
March 18, 2010
DS(ON)
FN7557.1