ISL6327A Datasheet, PDF (22/29 Pages) Intersil Corporation – Enhanced 6-Phase PWM Controller with 8-Bit VID Code and Differential Inductor DCR or Resistor Current Sensing

ISL6327A
.
VCC
R_TM1
TM
°C _RNTC
CHANNEL CURRENT SENSE
NON-LINEAR
A/D
I₆ I₅ I₄ I₃ I₂ I₁
K_i
D/A
ISEN6
ISEN5
ISEN4
ISEN3
ISEN2
ISEN1
R_TC1
TCOMP
R_TC2
4-BIT
A/D
XXXXXX
DROOP, I_OUT AND
OVERCURRENT PROTECTION
FIGURE 15. BLOCK DIAGRAM OF INTEGRATED
TEMPERATURE COMPENSATION
When the TM NTC is placed close to the current sense
component (inductor), the temperature of the NTC will track
the temperature of the current sense component. Therefore,
the TM voltage can be utilized to obtain the temperature of
the current sense component.
Based on VCC voltage, ISL6327A converts the TM pin
voltage to a 6-bit TM digital signal for temperature
compensation. With the non-linear A/D converter of
ISL6327A, TM digital signal is linearly proportional to the
NTC temperature. For accurate temperature compensation,
the ratio of the TM voltage to the NTC temperature of the
practical design should be similar to that in Figure 13.
Depending on the location of the NTC and the air-flowing,
the NTC may be cooler or hotter than the current sense
component. TCOMP pin voltage can be utilized to correct
the temperature difference between NTC and the current
sense component. When a different NTC type or different
voltage divider is used for the TM function, TCOMP voltage
can also be used to compensate for the difference between
the recommended TM voltage curve in Figure 14 and that of
the actual design. According to the VCC voltage, ISL6327A
converts the TCOMP pin voltage to a 4-bit TCOMP digital
signal as TCOMP factor N.
TCOMP factor N is an integer between 0 and 15. The
integrated temperature compensation function is disabled for
N = 0. For N = 4, the NTC temperature is equal to the
temperature of the current sense component. For N < 4, the
NTC is hotter than the current sense component. The NTC is
cooler than the current sense component for N > 4. When
N > 4, the larger TCOMP factor N, the larger the difference
between the NTC temperature and the temperature of the
current sense component.
ISL6327A 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 pin to match
the TM voltage vs temperature curve with the
recommended curve in Figure 13.
2. Run the actual board under the full load and the desired
cooling condition.
3. After the board reaches the thermal steady state, record
the temperature (T_CSC) of the current sense component
(inductor) and the voltage at TM and VCC pins.
4. Use Equation 19 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-----_{T---M-----x----R----T----M-----1-}
V_CC – V_TM
(EQ. 19)
5. Use Equation 20 to calculate the TCOMP factor N:
N
=
2----0---9----x---(_{---T----C----S----C-----}–_{-----T----N----T---C-----})
3xT_NTC + 400
+
4
(EQ. 20)
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 need the pull-down resistor R_TC2,
otherwise obtain R_TC2 using Equation 21:
R_TC2
=
-N----x----R----^T----^C----¹-
15 – N
(EQ. 21)
9. Run the actual board under full load again with the proper
resistors to TCOMP pin.
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.
External Temperature Compensation
By pulling the TCOMP pin to GND, the integrated
temperature compensation function is disabled. And one
external temperature compensation network, shown in
Figure 16, can be used to cancel the temperature impact on
the droop (i.e. load line).
22
FN6833.0
February 17, 2009