isl6262a Intersil Corporation, isl6262a Datasheet - Page 21

• Manufacturer Part Number: isl6262a
• Description: Two-phase Core Controller Santa Rosa, Imvp-6+
• Manufacturer: Intersil Corporation

Setting the Switching Frequency - FSET
The R
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
resistor that sets up the switching frequency of the converter
operating in CCM can be determined using Equation 4,
where R
For 300kHz operation, R
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.
R
ISEN1
OC
FSET
VDIFF
INTERNAL TO
ISL6262A
3
(
ISEN1
kΩ
modulator scheme is not a fixed frequency PWM
FSET
0.01µF
)
FIGURE 37. SIMPLIFIED SCHEMATIC FOR DROOP AND DIE SENSING WITH INDUCTOR DCR CURRENT SENSING
-
+
=
+
+
is in kΩ and the switching period is in µs.
(
ISEN2
period μs
10µA
R
OPN2
RTN
1
1
+
+
-
-
(
ISEN2
fset
330pF
) 0.29
–
330pF
is suggested to be 6.81kΩ. In
DROOP
VSEN
21
) 2.33
+
-
•
DROOP
OCSET
VSUM
DFB
R
VCC_SENSE
VSS_SENSE
opn1
VO'
R
drp2
R
OCSET
R
TO V
drp1
FSET
Cn
TO PROCESSOR
SOCKET KELVIN
CONNECTIONS
(EQ. 4)
OUT
R
VO'
R
SERIES
NTC
ISL6262A
VSUM
R
PAR
VO'
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.
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
V
FIGURE 38. CIRCUITRY ASSOCIATED WITH THE THERMAL
NTC
VSUM
VSUM
+
-
R
R
I
NTC
I
NTC
PHASE1
s
PHASE2
R
RS
THROTTLING FEATURE IN ISL6262A
S
1.24V
54µA
ISEN2
ISEN1
R
L
L2
R
SW2
2
L1
6µA
SW1
L 1
1.20V
+
-
VO'
+
Vdcr
C
C L1
L2
VO'
+
2
DCR
INTERNAL TO
Vdcr
DCR
-
ISL6262A
R
1
O1
-
R
O2
December 23, 2008
ESR
C
V
BULK
OUT
VR_TT#
FN6343.1