ISL6262A_14 Datasheet, PDF (21/28 Pages) Intersil Corporation – Two-Phase Core Controller(Santa Rosa, IMVP-6+)

ISL6262A
ISEN1
ISEN2
ISEN1
OC
ISEN2
10µA
-
+
INTERNAL TO
ISL6262A
+
1
+
-
+
1
+
-
RTN
OCSET
R_OCSET
VO'
VSUM
+
DROOP_{- DFB}
DROOP
R_drp2
VSEN
VSUM
R_SERIES
Cn
R_PAR
R_NTC
VDIFF
0.01µF
330pF
330pF
R_OPN2
VO'
R_drp1
VO'
R_opn1
TO V_OUT
VCC_SENSE
VSS_SENSE
TO PROCESSOR
SOCKET KELVIN
CONNECTIONS
I_PHASE1
R_S
VSUM
I_PHASE2
RS
VSUM
L1
R_L1
Vdcr₁
+-
DCR
CL1
R_O1
ISEN1
L₂
R_L2
ISEN2
VO'
DCR
+
-
Vdcr₂
R_O2
C_L2
VO'
V_OUT
C_BULK
ESR
FIGURE 37. SIMPLIFIED SCHEMATIC FOR DROOP AND DIE SENSING WITH INDUCTOR DCR CURRENT SENSING
Setting the Switching Frequency - FSET
The R³ modulator scheme is not a fixed frequency PWM
architecture. The switching frequency can increase during
the application of a load to improve transient performance.
It also varies slightly due to changes in input and output
voltage and output current, but this variation is normally less
than 10% in continuous conduction mode.
The resistor connected between the VW and COMP pins of
the ISL6262A adjusts the switching window, and therefore
adjusts the switching frequency (Figure 32). The R_FSET
resistor that sets up the switching frequency of the converter
operating in CCM can be determined using Equation 4,
where R_FSET is in kΩ and the switching period is in µs.
R_FSET(kΩ) = (period(μs) – 0.29) • 2.33
(EQ. 4)
For 300kHz operation, R_fset is suggested to be 6.81kΩ. In
discontinuous conduction mode (DCM), the ISL6262A runs in
period stretching mode. The switching frequency is dependent
on the load current level. In general, the lighter load, the slower
switching frequency. Therefore, the switching loss is much
reduced for the light load operation, which is important for
conserving the battery power in the portable application.
Voltage Regulator Thermal Throttling
lntel® IMVP-6+ technology supports thermal throttling of the
processor to prevent catastrophic thermal damage to the
voltage regulator. The ISL6262A features a thermal monitor
that senses the voltage change across an externally placed
negative temperature coefficient (NTC) thermistor.
Proper selection and placement of the NTC thermistor
allows for detection of a designated temperature rise by the
system.
Figure 38 shows the thermal throttling feature with
hysteresis. At low temperature, SW1 is on and SW2
connects to the 1.2V side. The total current going into NTC
pin is 60µA. The voltage on the NTC pin is higher than the
threshold voltage of 1.2V and the comparator output is low.
VR_TT# is pulling up high by the external resistor.
54µA 6µA
NTC
+
V_{NTC RNTC}
-
R_s
1.24V
SW1
VR_TT#
-
+
SW2
1.20V
INTERNAL TO
ISL6262A
FIGURE 38. CIRCUITRY ASSOCIATED WITH THE THERMAL
THROTTLING FEATURE IN ISL6262A
When the temperature increases, the NTC resistor value on
the NTC pin decreases. Thus, the voltage on the NTC pin
decreases to a level lower than 1.2V. The comparator output
changes polarity and turns SW1 off and connects SW2 to
1.24V. This pulls VR_TT# low and sends the signal to start
thermal throttle. There is a 6µA current reduction on the NTC
21
FN6343.1
December 23, 2008