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ADP3208D Datasheet(PDF) 33 Page - ON Semiconductor

Part No. ADP3208D
Description  7-Bit, Programmable, Dual-Phase, Mobile, CPU, Synchronous Buck Controller
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Maker  ONSEMI [ON Semiconductor]
Homepage  http://www.onsemi.com
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ADP3208D Datasheet(HTML) 33 Page - ON Semiconductor

 
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ADP3208D
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33
Selecting Thermal Monitor Components
To monitor the temperature of a single−point hot spot, set
RTTSET1 equal to the NTC thermistor’s resistance at the
alarm temperature. For example, if the alarm temperature
for VRTT is 100
°C and a Vishey thermistor
(NTHS−0603N011003J) with a resistance of 100 k
W at
25
°C, or 6.8 kW at 100°C, is used, the user can set RTTSET1
equal to 6.8 k
W (the RTH1 at 100°C).
Figure 45. Single−Point Thermal Monitoring
ADP3208D
31
30
TTSN
+
-
C TT
RTTSET1
RTH
VCC
5.0 V
VRTT
R
R
To monitor the temperature of multiple−point hot spots,
use the configuration shown in Figure 46. If any of the
monitored hot spots reaches the alarm temperature, the
VRTT signal is asserted. The following calculation sets the
alarm temperature:
RTTSET1 +
1
2 )
VFD
VREF
1
2 *
VFD
VREF
RTH1ALARMTEMPERATURE
(eq. 43)
where VFD is the forward drop voltage of the parallel diode.
Because the forward current is very small, the forward
drop voltage is very low, that is, less than 100 mV. Assuming
the same conditions used for the single−point thermal
monitoring example, that is, an alarm temperature of 100
°C
and use of an NTHS−0603N011003J Vishay thermistor;
solving Equation 43 gives a RTTSET of 7.37 kW, and the
closest standard resistor is 7.32 k
W (1%).
Figure 46. Multiple−Point Thermal Monitoring
ADP3208D
31
30
TTSN
+
-
C TT
R
TTSET1
R
TH1
VCC
5.0 V
VRTT
R
R
R
TTSET2
R
TH2
R
TTSET3
R
TH3
The number of hot spots monitored is not limited. The
alarm temperature of each hot spot can be individually set by
using different values for RTTSET1, RTTSET2, ... RTTSETn.
Tuning Procedure for ADP3208D
Set Up and Test the Circuit
1. Build a circuit based on the compensation values
computed from the design spreadsheet.
2. Connect a dc load to the circuit.
3. Turn on the ADP3208D and verify that it operates
properly.
4. Check for jitter with no load and full load
conditions.
Set the DC Load Line
1. Measure the output voltage with no load (VNL)
and verify that this voltage is within the specified
tolerance range.
2. Measure the output voltage with a full load when
the device is cold (VFLCOLD). Allow the board to
run for ~10 minutes with a full load and then
measure the output when the device is hot
(VFLHOT). If the difference between the two
measured voltages is more than a few millivolts,
adjust RCS2 using Equation 44.
RCS2(NEW) + RCS2(OLD)
VNL * VFLCOLD
VNL * VFLHOT
(eq. 44)
3. Repeat Step 2 until no adjustment of RCS2 is needed.
4. Compare the output voltage with no load to that
with a full load using 5 A steps. Compute the load
line slope for each change and then find the
average to determine the overall load line slope
(ROMEAS).
5. If the difference between ROMEAS and RO is more
than 0.05 m
W, use the following equation to adjust
the RPH values:
RPH(NEW) + RPH(OLD)
ROMEAS
RO
(eq. 45)
6. Repeat Steps 4 and 5 until no adjustment of RPH is
needed. Once this is achieved, do not change RPH,
RCS1, RCS2, or RTH for the rest of the procedure.
7. Measure the output ripple with no load and with a
full load with scope, making sure both are within
the specifications.
Set the AC Load Line
1. Remove the dc load from the circuit and connect a
dynamic load.
2. Connect the scope to the output voltage and set it
to dc coupling mode with a time scale of
100
ms/div.
3. Set the dynamic load for a transient step of about
40 A at 1 kHz with 50% duty cycle.
4. Measure the output waveform (note that use of a
dc offset on the scope may be necessary to see the
waveform). Try to use a vertical scale of
100 mV/div or finer.


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