ISL68201 Datasheet, PDF (18/32 Pages) Intersil Corporation – Single-Phase R4 Digital Hybrid PWM Controller

ISL68201
the respective power stage of the voltage regulator VR to sense
the operational temperature, and pull-up resistors are needed to
form the voltage dividers for the NTC pin. As the temperature of
the power stage increases, the resistance of the NTC will reduce,
resulting in the reduced voltage at the NTC pin. Figure 18 on
page 18 shows the TM voltage over the temperature for a typical
design with a recommended 10kΩ NTC (P/N:
NCP15XH103J03RC from Murata,  = 3380) and 1.54kΩ resistor
RTM. 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 3380 and RTM must be scaled accordingly. For instance, say
NTC = 20kΩ ( = 3380), then RTM should be
20kΩ/10kΩ*1.54kΩ = 3.08kΩ.
VCC
R_TM
NTC
ºC
R_NTC
BETA~ 3380
THERMAL TRIP
+136°C/+122ºC
+
-
OTP
ISL68201
FIGURE 16. BLOCK DIAGRAM OF THERMAL MONITORING AND
PROTECTION
The ISL68201 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, the ISL68201 utilizes the voltage at the NTC pin and
“TCOMP” register to compensate the temperature impact on the
sensed current. The block diagram of this function is shown in
Figure 17.
V_CC
R_TM
NTC
°C R_NTC
PLACE NTC
CLOSE TO
INDUCTOR
ISL68201
NON-LINEAR
A/D
D/A
k_i
CHANNEL
CURRENT
SENSE
I_PH
CSSEN
CSRTN
A/D
TCOMP
IOUT MONITOR AND
OVERCURRENT
PROTECTION
FIGURE 17. BLOCK DIAGRAM OF INTEGRATED TEMPERATURE
COMPENSATION
When the 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 NTC pin voltage
can be utilized to obtain the temperature of the current sense
component. Since the NTC could pick up noise from phase node,
a 0.1µF ceramic decoupling capacitor is recommended on the
NTC pin in close proximity to the controller.
Based on the V_CC voltage, the ISL68201 converts the NTC pin
voltage to a digital signal for temperature compensation. With
the nonlinear A/D converter of the ISL68201, the NTC digital
signal is linearly proportional to the NTC temperature. For
accurate temperature compensation, the ratio of the NTC voltage
to the NTC temperature of the practical design should be similar
to that in Figure 18.
100
90
80
70
60
50
40
30
20
0
20
40 60
80 100 120 140
TEMPERATURE (°C)
FIGURE 18. THE RATIO OF TM VOLTAGE TO NTC TEMPERATURE
WITH RECOMMENDED PART
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FN8696.1
March 7, 2016