isl8120 Intersil Corporation, isl8120 Datasheet - Page 25

• Manufacturer Part Number: isl8120
• Description: Dual/n-phase Buck Pwm Controller With Integrated Drivers
• Manufacturer: Intersil Corporation

Current Loop
When the ISL8120 operates in 2-phase mode, the current
control loop keeps the channel’s current in balance. After
175ns blanking period with respect to the falling edge of the
PWM pulse of each channel, the voltage developed across
the DCR of the inductor, r
or a precision resistor, is filtered and sampled for 175ns. The
current (I
provides feedback proportional to the average output current
of each channel.
For DCR sensing, the ICS can be derived from Equation 2:
ICS
VSEN2+
R
ISHARE
VSEN2-
ISET
=
ISET
IL DCR
------------------------ -
RISEN
CS1
•
VCC
/I
I
AVG_CS
CS2
700mV
ISEN1B
R
VOUT
ISEN1
) is scaled by the R
I
AVG_CS
+15µA
E/A
CURRENT
SHARE
BLOCK
FIGURE 13. SIMPLIFIED CURRENT SAMPLING AND OVERCURRENT PROTECTION
DS(ON)
+15µA
IOUT1
C
L1
25
V
ISHARE
PWM CONTROL
1V
CHANNEL 1
of the low-side MOSFETs,
ISEN1A
BLOCK
DCR1
DCR SENSING
ISEN
R
COMP
AVG_OC
PHASE1
resistor and
DCR1
AMP
I
CSH_ERR
7 CYCLES
SOFT-START &
DELAY
CORRECTION
-
FAULT LOGIC
CHANNEL 1
VOUT
CHANNEL 1
R
CURRENT
ISEN1
BLOCK
(EQ. 2)
ISEN1B
I
CS1
-
I
ISL8120
AVG_CS
OC1
COMP
IOUT1
L1
+
I
ISEN1A
TRIP
Rds(on) SENSING
DCR1
where IL is the inductor DC current, and DCR is its DC
resistance.
For low-side MOSFET r
derived from Equation 3:
In multiphase mode (VSEN2- pulled high), the scaled output
currents from both active channels are combined to create
an average current reference (I
average current of both channel outputs as calculated in
Equation 4.
ICS
IAVG
=105µA
=
=
PHASE1
IL r
--------------------------------- -
+
I
TRIP
ICS1
-----------------------------------
•
RISEN
∑
∑
2
DS ON
=105μA
I
AVG
I
I
I
AVG
AVG_CS
CSH_ERR
+
2
(
+
ICS2
PHASE2
= (I
)
OC2
COMP
CS1
I
CS2
= I
= (V
AVG
+
-
-
+ I
DS(ON)
ISARE
CS2
or I
DCR2
AMP
CORRECTION
) / 2
CS1
CHANNEL 2
CURRENT
- V
AVG
BLOCK
ISEN2A
sensing, the ICS can be
7 CYCLES
ISET
DELAY
DCR2
R
) which represents
)/G
CS
IOUT2
ISEN2B
L2
SOFT-START &
C
FAULT LOGIC
PWM CONTROL
CHANNEL 2
CHANNEL 2
BLOCK
March 28, 2008
R
ISEN2
VOUT
FN6641.0
(EQ. 3)
(EQ. 4)