cs5301 ON Semiconductor, cs5301 Datasheet - Page 17

• Manufacturer Part Number: cs5301
• Description: Three-phase Buck Controller With Integrated Gate Drivers And Power Good
• Manufacturer: ON Semiconductor

Current Limit
exceeds the voltage on the I
mode. For inductive sensing the I
set based on the inductor resistance (or current sense
resistor) at max temperature and max current. To set the level
of the I
When the sum of the Current Sense amplifiers (V
3. For resistive current sensing choose L and R
4. Calculate the high frequency output impedance
5. Adjust L and R
6.
provide a steady state ramp greater than 25 mV.
Again the ratio of L and R
L and R
(ConverterZ) of the converter during transients. This
is the impedance of the Output filter ESR in parallel
with the power stage output impedance (PwrstgZ)
and will indicate how far from the original level
(DVR) the output voltage will typically recover to
within one switching cycle. For a good transient
response DVR should be less than the peak output
voltage overshoot or undershoot.
where:
Multiply the converterZ by the output current step
size to calculate where the output voltage should
recover to within the first switching cycle after a
transient. If the ConverterZ is higher than the value
required to recover to where the adaptive positioning
is set the remainder of the recovery will be controlled
by the error amp compensation and will typically
recover in 10−20 ms.
Make sure that DVR is less than the expected peak
transient for a good transient response.
combination of transient response, steady state output
voltage ripple and pulse width jitter.
where:
For the overcurrent to work properly the inductor
time constant (L/R) should be ≤ the Current sense RC.
If the RC is too fast, during step loads the current
waveform will appear larger than it is (typically for a
few hundred ms) and may trip the current limit at a
level lower than the DC limit.
V ILIM +
LIM
R is R
I
OUT(LIM)
L R S + (V IN * V OUT )
pin:
ConverterZ +
PwrstgZ + R S
DVR + DI OUT
S
L
DVR + ConverterZ
will be a compromise.
or R
is the current limit threshold.
S;
L
or R
LIM
PwrstgZ
PwrstgZ ) ESR
S
as required to meet the best
pin the part will enter hiccup
CSA Gain 3
L
ConverterZ
LIM
is fixed and the values of
V OUT V IN
f
pin voltage should be
I OUT
ESR
25 mV
ITOTAL
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S
to
CS5301
)
17
Adaptive Positioning
adaptive positioning and current limit for a 250 kHz, 1.55 V,
60 A converter. The VID code is set to 1.6 V. Adaptive
positioning is set for 100 mV above DAC
below VID) at no load and 75 mV below the no load position
with a 60 A load. The peak output voltage transient should
be less than 100 mV during a 60 A step current. The
overcurrent limit is nominally 75 A.
Current Sensing, Power Stage and
Output Filter Components
Choose the component values for lossless current sensing,
7. To set the amount of voltage positioning above the
8. To set the difference in output voltage between no
1. Assume 1.5 mW of output filter ESR.
2.
3. n/a
4.
5. n/a
DAC setting at no load connect a resistor (R
between the output voltage and the V
R
See Figure 4 for V
load and full load, connect a resistor (R
between the V
calculated in two steps. First calculate the difference
between the V
voltage should be the same as the DAC voltage during
closed loop operation.) Then choose the R
source enough current across R
change in output voltage.
where:
Choose C + 0.01 mF
R + (V IN * V OUT )
L R L + R
Choose R L + 2.0 mW
L + R L
PwrstgZ + R L
ConverterZ +
DVR + ConverterZ
DV VDRP + R
VFB
R = R
I
+ (12 * 1.55)
+ 21.5 kW å Choose 20 kW
OUT
R VDRP + DV VDRP
+ 1.0 mW
as;
R VFB + NL Position V FB Bias Current
is the full load output current.
L
+ 2.0 mW
or R
R
DESIGN EXAMPLE
+ 2.8 mW
C + 20 kW
S
DRP
PwrstgZ
PwrstgZ ) ESR
2.8 mW ) 1.5 mW
C + 2.0 mW
for one phase;
DRP
CSA Gain 3
I OUT
FB
and V
250 k
60 A + 60 mV
and V
f
Bias Current.
4.2 3.0 + 2.8 mW
I OUT
V OUT V IN
FB
C
1.5 mW
ESR
R V(FB) DV OUT
0.01 mF + 200 ms
0.01 mF
CS to V DRP Gain
1.55 12
FB
pin at full load. (The V
25 mV
200 ms + 400 nH
pins. R
VFB
^ 1.0 mW
OUT
25 mV
for the desired
FB
VDRP
pin. Choose
(or 25 mV
VDRP
can be
VDRP
VFB
FB
to
)
)