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ADP3207 Datasheet(PDF) 12 Page - ON Semiconductor

Part No. ADP3207
Description  CPU Synchronous Buck Controller
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Maker  ONSEMI [ON Semiconductor]
Homepage  http://www.onsemi.com
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ADP3207 Datasheet(HTML) 12 Page - ON Semiconductor

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ADP3207
Rev. 1 | Page 12 of 29 | www.onsemi.com
Table 4. Phase Number and Operation Modes
PSI
DPRSLP
VID Transient
Period1
Hit Current
Limit
No. of Phases
Selected by User
No. of Phases
in Operation
Operation Mode
DNC2
DNC2
Yes
DNC2
N 3, 2, or 1
N
PWM, CCM3 only
1
0
No
DNC2
N 3, 2, or 1
N
PWM, CCM3 only
0
0
No
No
DNC2
Phase 1 only
RPM, CCM3 only
0
0
No
Yes
DNC2
N
PWM, CCM3 only
DNC2
1
No
No
DNC2
Phase 1 only
RPM, automatic CCM3/DCM4
DNC2
1
No
Yes
DNC2
N
PWM, CCM3 only
1 VID transient period is the time period following any VID change, including entrance and exit of deeper sleep mode. The duration of VID transient period is the same
as that of PWRGD masking time.
2 DNC means do not care.
3 CCM means continuous conduction mode
4 DCM means discontinuous conduction mode.
SWITCH FREQUENCY SETTING
Master Clock Frequency for PWM Mode
The clock frequency of the ADP3207 is set by an external
resistor connected from the RT pin to ground. The frequency
varies with the VID voltage: the lower the VID voltage, the
lower the clock frequency. The variation of clock frequency
with VID voltage makes VCORE ripple remain constant and
improves power conversion efficiency at a lower VID voltage.
Figure 6 shows the relationship between clock frequency and
VID voltage, parameterized by RT resistance.
To determine the switching frequency per phase, the clock is
divided by the number of phases in use. If PWM3 is pulled up
to VCC, then the master clock is divided by 2 for the frequency
of the remaining phases. If PWM2 and PWM3 are pulled up to
VCC, then the switching frequency of a Phase 1 equals the
master clock frequency. If all phases are in use, divide by 3.
Switching Frequency for RPM Mode–Phase 1
When ADP3207 operates in single-phase RPM mode, its
switching frequency is not controlled by the master clock, but
by the ripple voltage on the COMP pin. The PWM1 pin is set
high each time the COMP pin voltage rises to a voltage limit
determined by the VID voltage and the external resistance
connected between Pin VRPM and Pin RRPM. Whenever
PWM1 pin is high, an internal ramp signal rises at a slew rate
programmed by the current flowing into the RAMPADJ pin.
Once this internal ramp signal hits the COMP pin voltage, the
PWM1 pin is reset to low.
In continuous current mode, the switching frequency of RPM
operation is maintained almost constantly. While in
discontinuous current mode, the switching frequency reduces
with the load current.
OUTPUT VOLTAGE DIFFERENTIAL SENSING
The ADP3207 combines differential sensing with a high accuracy,
VID DAC, precision REF output and a low offset error amplifier to
meet the rigorous accuracy requirement of the Intel IMVP-6
specification. In steady-state, the VID DAC and error amplifier
meet the worst-case error specification of ±10 mV over the full
operating output voltage and temperature range.
The CPU core output voltage is sensed between the FB and
FBRTN pins. Connect FB through a resistor to the positive
regulation point, usually the VCC remote sense pin of the
microprocessor. Connect FBRTN directly to the negative
remote sense point, the VSS sense point of the CPU. The
internal VID DAC and precision voltage reference are
referenced to FBRTN, and have a maximum current of 200 μA
to guarantee accurate remote sensing.
OUTPUT CURRENT SENSING
The ADP3207 provides a dedicated current-sense amplifier
(CSA) to monitor the total output current of the converter for
proper voltage positioning vs. load current, and for current-
limit detection. Sensing the load current being delivered to the
load is inherently more accurate than detecting peak current or
sampling the current across a sense element, such as the low-
side MOSFET. The current-sense amplifier can be configured
several ways depending on system requirements.
Output inductor ESR sensing without use of a thermistor
for lowest cost
Output inductor ESR sensing with use of a thermistor that
tracks inductor temperature to improve accuracy
Discrete resistor sensing for highest accuracy
The positive input of the CSA is connected to the CSREF pin,
which is connected to the output voltage. At the negative input
CSSUM pin of the CSA, signals from the sensing element (that
is, in case of inductor RDC sensing, signals from the switch


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