ISL6307A Datasheet, PDF (26/33 Pages) Intersil Corporation – Ultra-high bandwidth 6-Phase PWM Controller with 8 Bit VID Code Capable of Precision RDS(ON) or DCR Differential Current Sensing

ISL6307A
ISL6307A multiplexes the TCOMP factor N with the TM
digital signal to obtain the adjustment gain to compensate
the temperature impact on the sensed channel current. The
compensated channel current signal is used for droop and
overcurrent protection functions.
Design procedure:
1. Properly choose the voltage divider for TM to match the
TM voltage vs. temperature curve with the recommended
curve in Figure 19.
2. Run the actual board under the full load and the desired
cooling conditions.
3. After the board reaches the thermal steady state, record
the temperature (T_CSC) of the current sense component
(inductor or MOSFET) and TM voltage and Vcc.
4. Use the following equation to calculate the resistance of
the TM NTC, and find out the corresponding NTC
temperature T_NTC from the NTC datasheet.
R_NTC(TNTC) = ^V-_V----^T-_C--^M--_C---^x--_–--^R---_V-^T---_T-^M--_M---¹-
(EQ. 21)
5. Use the following equation to calculate the TCOMP factor
N.
N = ²----⁰---⁹--₃--^x--_x-⁽--_T-^T---_N-^C---_T-^S---_C-^C----₊-^–----₄-^T--₀--^N--₀--^T---^C-----⁾ + 4
(EQ. 22)
6. Choose an integral number close to the above result for
the TCOMP factor. If this factor is higher than 15, use
N=15. If it is less than 1, use N=1.
7. Choose the pull-up resistor R_TC1 (typical 10kΩ).
8. If N=15, do not use the pull-down resistor R_TC2.
Otherwise obtain R_TC2 by the following equation.
R_TC2 = -^N---₁-^x--₅--^R---_–-^T---_N-^C----¹-
(EQ. 23)
9. Run the actual board under full load again with the proper
resistors to TCOMP.
10. 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.
11. If the output voltage increases over 2mV as the
temperature increases, i.e. V2-V1>2mV, reduce N and
redesign R_TC2. If the output voltage decreases over 2mV
as the temperature increases, i.e. V1-V2>2mV, increase
N and redesign R_TC2.
The design spreadsheet is available for those calculations.
Please contact Intersil to get the spreadsheet.
External Temperature Compensation
By setting the voltage of TCOMP to 0, the integrated
temperature compensation function is disabled. In this case,
an external temperature compensation network, as shown in
Figure 22, can be used to cancel the temperature impact on
the droop (i.e. load-line).
C₂ (OPTIONAL)
V_DROOP
R_C ^CC
COMP
EXTERNAL TCOMP
COMPENSATION
NETWORK
NTC
R₁
R_T
R₂
R₃
+
R_FB
-
FB
IDROOP
VDIFF
FIGURE 22. TEMPERATURE COMPENSATION WITH
EXTERNAL NTC NETWORK
The sensed current will flow out of the IDROOP pin and
develop the droop voltage across the resistor, R_FB, between
FB and VDIFF. 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 non-linear
temperature characteristics of the NTC, a resistor network is
needed to make the equivalent resistance between FB and
VDIFF pins reverse proportional to the temperature.
The external temperature compensation network can only
compensate the temperature impact on the droop, while it
has no impact to the sensed current inside ISL6307A.
Therefore this network cannot compensate for the
temperature impact on the over current protection function.
To simplify the design for external NTC network parameters,
Excel calculation tools have been developed. Please contact
Intersil to get the tools.
General Design Guide
This design guide is intended to provide a high-level
explanation of the steps necessary to create a multiphase
power converter. It is assumed that the reader is familiar with
many of the basic skills and techniques referenced below. In
addition to this guide, Intersil provides complete reference
designs that include schematics, bills of materials, and
example board layouts for all common microprocessor
applications.
Power Stages
The first step in designing a multiphase converter is to
determine the number of phases. This determination
depends heavily on the cost analysis which in turn depends
on system constraints that differ from one design to the next.
Principally, the designer will be concerned with whether
components can be mounted on both sides of the circuit
26
FN9236.0
February 6, 2006