ISL6334AR5368 Datasheet, PDF (24/31 Pages) Intersil Corporation – VR11.1, 4-Phase PWM Controller with Light Load Efficiency Enhancement and Load Current Monitoring Features

ISL6334AR5368
V_CC
R _TM1
TM
o_c
R
NTC
V_CC
R
TC1
TCOMP
R
TC2
NON-LINEAR
A/D
CHANNEL
CURRENT
SENSE
I₄
I₃
I₂
I_sen4
I_sen3
I_sen2
I_sen1
I₁
D/A
k_i
4-BIT
A/D
DROOP 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, ISL6334AR5368 converts the TM
pin voltage to a 6-bit TM digital signal for temperature
compensation. With the non-linear A/D converter of
ISL6334AR5368, the 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 airflow, the
NTC may be cooler or hotter than the current sense
component. The 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, the
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, ISL6334AR5368 converts the TCOMP pin
voltage to a 4-bit TCOMP digital signal as TCOMP factor N.
The 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.
ISL6334AR5368 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 the 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 or MOSFET) and the voltage at TM and VCC
pins.
4. Use Equation 21 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_C
C
–
V
TM
(EQ. 21)
5. Use Equation 22 to calculate the TCOMP factor N:
N
=
2----0---9----x---(_{---T----C----S----C-----}–_{-----T----N----T---C-----})
3xT_NTC + 400
+
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, one does not need the pull-down resistor R_TC2.
If otherwise, obtain R_TC2 using Equation 23:
R_TC2
=
-N----x----R----^T----^C----¹-
15 – N
(EQ. 23)
9. Run the actual board under full load again with the proper
resistors connected to the 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.
External Temperature Compensation
By pulling the TCOMP pin to GND, the integrated
temperature compensation function is disabled. In addition,
one external temperature compensation network, shown in
Figure 16, can be used to cancel the temperature impact on
the droop (i.e., load line).
24
FN6839.2
September 7, 2010