ISL68200 Datasheet, PDF (18/32 Pages) Intersil Corporation – Single-Phase R4 Digital Hybrid PWM Controller with Integrated Driver

ISL68200
VCC
RTM
NTC
ºC
RNTC
BETA~ 3380
THERMAL TRIP
+136°C/+122ºC
OTP
ISL68200
FIGURE 16. BLOCK DIAGRAM OF THERMAL MONITORING AND
PROTECTION
The ISL68200 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 ISL68200 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.
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
Since the NTC attaches to the PCB, but not directly to the current
sensing component, it inherits high thermal impedance between
the NTC and the current sensing element. The “TCOMP” register
values can be utilized to correct the temperature difference
between NTC and the current sense component. As shown in
Figure 19, the NTC should be placed in proximity to the output
rail; DON’T place it close to the MOSFET side, which generates
much more heat.
V_CC
R_TM
NTC
o_{c RNTC}
PLACE NTC
CLOSE TO
INDUCTOR
ISL68200
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 the phase
node, a 0.1µF ceramic decoupling capacitor is recommended on
the NTC pin in close proximity to the controller.
Based on the VCC voltage, the ISL68200 converts the NTC pin
voltage to a digital signal for temperature compensation. With
the nonlinear A/D converter of the ISL68200, the NTC digital
signal is linearly proportional to the NTC temperature. For
accurate temperature compensation, the ratio of the NTC voltage
VOUT
NTC
OUTPUT
INDUCTOR
POWER STAGE
FIGURE 19. RECOMMENDED PLACEMENT OF NTC
The ISL68200 multiplexes the “TCOMP” value with the NTC
digital signal to obtain the adjustment gain to compensate the
temperature impact on the sensed channel current. The
compensated current signal is used for I_OUT and overcurrent
protection functions. The TCOMP “OFF” code is to disable thermal
compensation when the current sensing element is the resistor
or smart power stage (internally thermal compensated) that has
little thermal drifting.
TABLE 8. “TCOMP” VALUES
D1h
TCOMP (°C)
D1h
TCOMP (°C)
0h
30
2h
5
1h
15
3h
OFF
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FN8705.1
March 7, 2016