ISL6306 Datasheet, PDF (25/33 Pages) Intersil Corporation – 4-Phase PWM Controller with 8-Bit DAC Code Capable of Precision rDS ON or DCR Differential Current Sensing

ISL6306
V_TM/V_CC vs TEMPERATURE
100
90
80
70
60
50
40
30
20
0
20
40
60
80 100 120 140
TEMPERATURE (°C)
FIGURE 15. THE RATIO OF TM VOLTAGE TO NTC
TEMPERATURE WITH RECOMMENDED PARTS
TM
0.39*V_CC
0.33*V_CC
0.28*V_CC
VR_FAN
VR_HOT
TEMPERATURE (°C)
T1 T2 T3
FIGURE 16. VR_HOT AND VR_FAN SIGNAL vs TM VOLTAGE
Based on the NTC temperature characteristics and the
desired threshold of VR_HOT signal, the pull-up resistor
RTM1 of TM pin is given by:
R_TM1 = 2.75xR_NTC(T3)
(EQ. 17)
R_NTC(T3) is the NTC resistance at the VR_HOT threshold
temperature T3.
The NTC resistance at the set point T2 and release point T1
of VR_FAN signal can be calculated as:
R_NTC(T2) = 1.267xR_NTC(T3)
(EQ. 18)
R_NTC(T1) = 1.644xR_NTC(T3)
(EQ. 19)
With the NTC resistance value obtained from Equations 18
and 19, the temperature value T2 and T1 can be found from
the NTC datasheet.
Temperature Compensation
ISL6306 supports inductor DCR sensing, MOSFET r_DS(ON)
sensing, or resistive sensing techniques. Both inductor DCR
and MOSFET r_DS(ON) have the positive temperature
coefficient, which is about +0.38%/°C. Because the voltage
across inductor or MOSFET is sensed for the output current
information, the sensed current has the same positive
temperature coefficient as the inductor DCR or MOSFET
r_DS(ON).
In order to obtain the correct current information, there
should be a way to correct the temperature impact on the
current sense component. ISL6306 provides two methods:
integrated temperature compensation and external
temperature compensation.
Integrated Temperature Compensation
When TCOMP voltage is equal or greater than VCC/15,
ISL6306 will utilize the voltage at TM and TCOMP pins to
compensate the temperature impact on the sensed current.
The block diagram of this function is shown in Figure 17.
V_CC
R_TM1
TM
o_c
R_NTC
V_CC
R_TC1
TCOMP
R_TC2
NNOoNn--LliINnEeAaRr
AA/D
Cha^Cn^Hn^Ael^Nc^Nu^Er^Lrent
C_sU_eR_nR_sE_eNT
SENSE
I₄
I₃
I₂
I₁
I_sen4
I_sen3
I_sen2
I_sen1
D/A
k_i
44--BbITit
AA//DD
DROOP A_DND_roO_oV_pE_&RCURRENT
Over cPuRrOreTnEtCpTrIOoNtection
FIGURE 17. BLOCK DIAGRAM OF INTEGRATED
TEMPERATURE COMPENSATION
When the TM NTC is placed close to the current sense
component (inductor or MOSFET), 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, ISL6306 converts the TM pin voltage
to a 6-bit TM digital signal for temperature compensation.
With the non-linear A/D converter of ISL6306, 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 15.
25
FN9226.1
May 5, 2008