MAX17009GTL+T Maxim Integrated Products, MAX17009GTL+T Datasheet - Page 36

• Manufacturer Part Number: MAX17009GTL+T
• Description: IC CTLR VIDEO SERIAL DUAL 40TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX17009GTL+T

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

where I
and f
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. If using a
swinging inductor (where the inductance decreases lin-
early with increasing current), evaluate the LIR with
properly scaled inductance values. For the selected
inductance value, the actual peak-to-peak inductor rip-
ple current (ΔI
Ferrite cores are often the best choice, although pow-
dered iron is inexpensive and can work well at 200kHz.
The core must be large enough not to saturate at the
peak inductor current (I
The MAX17009 overcurrent protection employs a peak
current-sensing algorithm that uses either current-
sense resistors or the inductor’s DCR as the current-
sense element (see the Current Sense section). Since
the controller limits the peak inductor current, the maxi-
mum average load current is less than the peak cur-
rent-limit threshold by an amount equal to half the
inductor ripple current. Therefore, the maximum load
capability is a function of the current-sense resistance,
inductor value, switching frequency, and input-to-out-
put voltage difference. When combined with the output
undervoltage-protection circuit, the system is effectively
protected against excessive overload conditions.
The peak current-limit threshold is set by voltage differ-
ence between ILIM and REF using an external resistor-
divider:
where R
sense element (inductors’ DCR or current-sense resis-
tor), and I
phase). The peak current-limit threshold voltage-adjust-
ment range is from 10mV to 50mV.
AMD Mobile Serial VID Dual-Phase
Fixed-Frequency Controller
36
V
______________________________________________________________________________________
SW
CS(PK)
LOAD(MAX)
is the switching frequency per phase.
SENSE
I
PEAK
LIMIT(PK)
Peak-Inductor Current Limit (ILIM)
L
ΔI
= V
I
=
INDUCTOR
LIMIT(PK)
INDUCTOR
=
⎛
⎜
⎝
CSP
is the resistance value of the current-
f
⎛
⎜
⎝
SW LOAD MAX
I
LOAD MAX
is the desired peak current limit (per
is the maximum current per phase,
_ - V
I
V
IN
η
PH
= V
−
PEAK
(
CSN
=
) is defined by:
V
(
OUT
V
CS(PK)
OUT IN
_ = 0.05 x (V
)
):
⎞
⎟ +
⎠
)
LIR
V f
(
IN SW
V
⎛
⎜
⎝
/ R
Δ
⎞
⎟
⎠
⎛
⎜
⎝
I
INDUCTOR
−
SENSE
V
L
V
V
OUT
IN
OUT
2
REF
⎞
⎟
⎠
)
- V
⎞
⎟
⎠
ILIM
)
The output filter capacitor must have low-enough ESR
to meet output ripple and load-transient requirements.
In CPU V
the output is subject to large-load transients, the output
capacitor’s size typically depends on how much ESR is
needed to prevent the output from dipping too low
under a load transient. Ignoring the sag due to finite
capacitance:
In non-CPU applications, the output capacitor’s size
often depends on how much ESR is needed to maintain
an acceptable level of output ripple voltage. The output
ripple voltage of a step-down controller equals the total
inductor ripple current multiplied by the output capaci-
tor’s ESR. When operating multiphase systems out-of-
phase, the peak inductor currents of each phase are
staggered, resulting in lower output-ripple voltage
(V
For nonoverlapping, multiphase operation (V
the maximum ESR to meet the output-ripple-voltage
requirement is:
where f
actual capacitance value required relates to the physi-
cal size needed to achieve low ESR, as well as to the
chemistry of the capacitor technology. Thus, the
capacitor selection is usually limited by ESR and volt-
age rating rather than by capacitance value (this is true
of polymer types).
The capacitance value required is determined primarily
by the output transient-response requirements. Low
inductor values allow the inductor current to slew faster,
replenishing charge removed from or added to the out-
put filter capacitors by a sudden load step. Therefore,
the amount of output soar when the load is removed is
a function of the output voltage and inductor value. The
minimum output capacitance required to prevent over-
shoot (V
calculated as:
RIPPLE
SW
) by reducing the total inductor ripple current.
SOAR
CORE
R
is the switching frequency per phase. The
ESR
(
R
) due to stored inductor energy can be
ESR
C
converters and other applications where
≤
OUT
⎡
⎢
⎢
⎣
+
(
V
Output-Capacitor Selection
R
IN
≥
PCB
(
−
V f
Δ
2
V
IN SW
I
LOAD MAX
)
OUT
V
≤
OUT SOAR
Δ
L
)
I
LOAD MAX
(
V
V
OUT
V
STEP
)
(
)
⎤
⎥
⎥
⎦
2
V
L
RIPPLE
)
IN
≥ V
OUT
),