ISL6366 Datasheet, PDF (30/44 Pages) Intersil Corporation – Dual 6-Phase + 1-Phase PWM Controller for VR12/IMVP7 Applications

ISL6366
VCC
R_TM
R_NTC1
o_c
TM
R_TMS
TMS
Thermal Trip
Point Lookup
Table (90-120⁰C)
TMAX
VR_HOT#
o_c RNTC2
ISL6366
NTC BETA ~ 3477
FIGURE 19. BLOCK DIAGRAM OF THERMAL MONITORING
FUNCTION
The diagram of thermal monitoring function block is shown in Figure
19. One NTC resistor should be placed close to the respective power
stage of the voltage regulator VR0 and VR1 to sense the operational
temperature, and one pull-up resistor is needed to form the voltage
divider for the TM pin. As the temperature of the power stage
increases, the resistance of the NTC will reduce, resulting in the
reduced voltage at the TM pin. Figure 20 shows the TM voltage over
the temperature for a typical design with a recommended 6.8kΩ
NTC (P/N: NTHS0805N02N6801 from Vishay, β = 3477) and 1kΩ
resistor R_TM. It is recommended to use those resistors for the
accurate temperature compensation since the internal thermal
digital code is developed based upon these two components. If a
different value is used, the temperature coefficient must be close to
3477 and R_TM must be scaled accordingly. For instance, say
NTC = 10kΩ (β = 3477), then R_TM should be 10kΩ/6.8kΩ*1kΩ =
1.47kΩ.
There is a comparator with hysteresis to compare the TM pin
voltage to the threshold set by the TMAX register for VR_HOT#
signal. With TMAX set at +100°C, the VR_HOT# signal is pulled
to GND when either TM or TMS voltage is lower than 39.12% of
VCC voltage, and is open when both TM and TMS voltages
increase to above 40.98% of VCC voltage. The comparator trip
point will be programmable by TMAX values. Figure 20 shows the
operation of those signals.
100
90
80
70
60
50
40
30
20
0 20 40 60 80 100 120 140
TEMPERATURE (^oC)
FIGURE 20. THE RATIO OF TM VOLTAGE TO NTC TEMPERATURE
WITH RECOMMENDED PARTS
TM
40.98%*VCC
39.12%*VCC
VR_HOT#
TEMPERATURE
T1 T2
FIGURE 21. VR_HOT# SIGNAL (TMAX = 100°C) vs TM VOLTAGE
Based on the NTC temperature characteristics and the desired
threshold of the VR_HOT# signal, the pull-up resistor R_TM of TM
pin is given by Equation 21:
R_TM = 1.557xR_NTC(T2)
(EQ. 21)
R_NTC(T2) is the NTC resistance at the VR_HOT# threshold
temperature T2. The VR_HOT# is de-asserted at temperature T1,
as shown in Table 7. Since the NTC directly senses the
temperature of the PCB and not the exact temperature of the
hottest component on the board due to airflow and varied
thermal impedance, therefore, the user should select a lower
TMAX number, depending upon the mismatching between NTC
and the hottest components, than such component to guarantee
a safe operation.
TABLE 7. VR_HOT# TYPICAL TRIP POINT AND HYSTERESIS
TMAX
(°C)
VR_HOT# LOW (°C; VR_HOT# OPEN
T2, %VCC)
(°C; T1, %VCC)
HYSTERESIS
(°C)
90
88.6; 45.52%
85.9; 47.56%
2.7
95
94.3; 42.26%
91.4; 44.20%
2.9
100
100.0; 39.12%
97.1; 40.98%
2.9
105
106.1; 36.14% 103.0; 37.92%
3.1
110
109.1; 33.32% 106.1; 35.00%
3.0
115
115.5; 30.68% 112.3; 32.24%
3.2
120
118.7; 28.24%
115.5; 29.7%
3.2
Temperature Compensation
The ISL6366 supports inductor DCR sensing, or resistive sensing
techniques. The inductor DCR has a positive temperature
coefficient, which is about +0.385%/°C. Since the voltage across
the inductor is sensed for the output current information, the
sensed current has the same positive temperature coefficient as
the inductor DCR.
In order to obtain the correct current information, there should be
a way to correct the temperature impact on the current sense
component. ISL6366 provides two methods: integrated
temperature compensation and external temperature
compensation.
30
FN6964.0
January 3, 2011