ISL6565A Datasheet, PDF (16/28 Pages) Intersil Corporation – Multi-Phase PWM Controller with Precision rDS(ON) or DCR Current Sensing for VR10.X Application

ISL6565A, ISL6565B
The ISL6565A, ISL6565B checks the VID inputs six times
every switching cycle. If the VID code is found to have
changed, the controller waits half of a complete cycle before
executing a 12.5mV change. If during the half-cycle wait
period, the difference between the DAC level and the new
VID code changes sign, no change is made. If the VID code
is more than 1 bit higher or lower than the DAC (not
recommended), the controller will execute 12.5mV changes
six times per cycle until VID and DAC are equal. It is
important to carefully control the rate of VID stepping in 1-bit
increments.
In order to ensure the smooth transition of output voltage
during VID change, a VID step change smoothing network is
required for an ISL6565A, ISL6565B based voltage
regulator. This network is composed of a 1kΩ internal
resistor between the output of DAC and the capacitor C_REF,
between the REF pin and ground. The selection of C_REF is
based on the time duration for 1 bit VID change and the
allowable delay time.
Assuming the microprocessor controls the VID change at 1
bit every T_VID, the relationship between C_REF and T_VID is
given by Equation 15.
C_REF = 0.004X T_VID
(EQ. 15)
As an example, for a VID step change rate of 5µs per bit, the
value of C_REF is 22nF based on Equation 15.
Temperature Compensation
MOSFET r_DS(ON) and inductor DCR are both susceptible to
changes in value due to temperature. Since output voltage
positioning is derived from the channel current sensed
across these two elements, any variation in resistance
results in a corresponding error in the output voltage.
The temperature coefficient, α, of the r_DS(ON) or DCR is the
parameter that determines how much the resistance varies
with temperature. As temperature increases above ambient,
the average sensed current, I_AVG, changes in proportion to
the temperature coefficient and temperature rise as shown in
Equation 16.
I_AVG = I_{AVG(TAMBIENT)} ⋅ [1 + α(T – T_AMBIENT)]
(EQ. 16)
With this resulting error, I_AVG can now be described as the
sum of two parts, the average sensed current at ambient
temperature and the resulting error current, I_ERR, due to the
temperature rise.
I_ERR(T) = I_{AVG(TAMBIENT)} ⋅ α ⋅ (T – T_AMBIENT)
(EQ. 17)
In order to compensate for this error current, the ISL6565A,
ISL6565B includes a temperature compensation circuit that
injects a current, I_TCOMP, into the FB pin. This current is
created by pushing the average sense current through a
selectable external resistor, R_TCOMP.
VDIFF
-
V_DROOP
+
R_FB
FB
I_DROOP
I_AVG
K_TC
I_TCOMP
TCOMP
R_TCOMP
I_AVG
ISL6565A, ISL6565B
FIGURE 10. TEMPERATURE COMPENSATION CIRCUITRY
As shown in Figure 10, the voltage drop developed across
R_TCOMP is then sensed and multiplied by a known gain,
K_TC, which is determined by the internal IC temperature.
This gain creates the temperature compensation current,
I_TCOMP, that is injected into the FB pin.
I_TCOMP = K_TC ⋅ (T – 25) ⋅ I_AVG ⋅ R_TCOMP
(EQ. 18)
Select R_TCOMP such that I_TCOMP equals I_ERR over the
entire range of operating temperature. The resulting droop
current accurately represents the load current; achieving a
linear, temperature-independant load line.
Initialization
Prior to initialization, proper conditions must exist on the
enable inputs and VCC. When the conditions are met, the
controller begins soft-start. Once the output voltage is within
the proper window of operation, the controller asserts
PGOOD.
Enable and Disable
While in shutdown mode, the PWM outputs are held in a
high-impedance state to assure the drivers remain off. The
following input conditions must be met before the ISL6565A,
ISL6565B is released from shutdown mode.
1. The bias voltage applied at VCC must reach the internal
power-on reset (POR) rising threshold. Once this
threshold is reached, proper operation of all aspects of
the ISL6565A, ISL6565B is guaranteed. Hysteresis
between the rising and falling thresholds assure that once
enabled, the ISL6565A, ISL6565B will not inadvertently
turn off unless the bias voltage drops substantially (see
Electrical Specifications).
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