ISL6364 Datasheet, PDF (32/44 Pages) Intersil Corporation – Dual 4-Phase + 1-Phase PWM Controller for VR12/IMVP7 Applications

ISL6364
4. Use Equation 23 to calculate the resistance of the NTC, and
find out the corresponding NTC temperature T_NTC from the
NTC datasheet or using Equation 24, where β is equal to 3477
for recommended NTC.
R_NTC(T_NTC)
=
-^V----^T--^M-----^x---^R----^T---^M---
V_CC
–
V
T
M
(EQ. 23)
T_NTC
=
---------------------------------^β-----------------------------------
ln
⎛
⎝
R^-----_N^---_T^--R-_C^----T(^--T^-M--_N^----_T^---_C^----)⎠⎞
+
--------^β----------
298.15
–
273.15
(EQ. 24)
5. In Intersil designed worksheet, choose a number close to the
result as in Equation 25 in the “TCOMP” cell to calculate the
needed resistor network for the register “TCOMP” pin. (Note:
for worksheet, please contact Intersil Application support at
www.intersil.com/design/).
T_COMP = T_CSC – T_NTC
(EQ. 25)
6. Run the actual board under full load again with the proper
resistors connected to the “TCOMP” pin.
7. Record the output voltage as V1 immediately after the output
voltage is stable with the full load. Record the output voltage
as V2 after the VR reaches the thermal steady state.
8. If the output voltage increases over 2mV as the temperature
increases, i.e. V2 - V1 > 2mV, reduce “TCOMP” value; if the
output voltage decreases over 2mV as the temperature
increases, i.e. V1 - V2 > 2mV, increase “TCOMP” values.
External Temperature Compensation
When the “OFF” code of TCOMP is selected, then the internal
current source is not thermally compensated, i.e, the integrated
temperature compensation function is disabled. However, one
external temperature compensation network, shown in Figure
24, can be used to cancel the temperature impact on the droop
(i.e., load line).
the equivalent resistance between the FB pin and VOUT sensing
node inversely proportional to the temperature.
This external temperature compensation network can only
compensate the temperature impact on the droop, while it has no
impact to the sensed current inside ISL6364. Therefore, this
network cannot compensate for the temperature impact on the
overcurrent protection function. In addition, NTC could pick up
phase switching noise and easily inject into the loop. This method
is typically not recommended.
PHASE
ISENS-
o_C
ISL6364
ISENS+
FIGURE 25. NTC WITH L/DCR MATCHING NETWORK FOR
THERMAL COMPESNATION
Furthermore, the NTC can be placed with L/DCR matching
network to thermally compensate the sensed current, or with
IMON network to thermally compensate the IMON voltage
(typically need to set internal overcurrent trip higher than IMON
OCP trip), as shown in Figures 25 and 26, respectively. These
methods are typically applicable to both VR0 and VR1 for
non-droop applications.
IMON
COMP
ISL6364
FB
o_C
ID R O O P
VOUT
FIGURE 24. EXTERNAL TEMPERATURE COMPENSATION FOR
LOAD LINE
The sensed current will flow out of the FB pin and develop a droop
voltage across the resistor equivalent (R_FB) between the FB pin
and VOUT sensing node. If R_FB resistance reduces as the
temperature increases, the temperature impact on the droop can
be compensated. An NTC resistor can be placed close to the power
stage and used to form R_FB. Due to the nonlinear temperature
characteristics of the NTC, a resistor network is needed to make
ISL6364
o_C
FIGURE 26. NTC WITH IMON NETWORK FOR THERMAL
COMPESNATION
Hard-wired Registers (Patent
Pending)
To set registers for VR12/IMVP7 applications using lowest pin-
count package and with lowest overall cost, Intersil has
developed a high resolution ADC using a patented technique with
simple 1%, 100ppm/k or better temperature coefficient resistor
divider, as shown in Figure 27. The same type of resistors are
preferred so that it has similar change over temperature. In
addition, the divider is comparing to the internal divider off VCC
and GND nodes and therefore must refer to VCC and GND pins,
not through any RC decoupling network.
32
FN6861.0
December 22, 2010