LM2642MTC/NOPB

Manufacturer Part NumberLM2642MTC/NOPB
DescriptionIC CTRLR SW SYNC STPDN 28TSSOP
ManufacturerNational Semiconductor
LM2642MTC/NOPB datasheet
 


Specifications of LM2642MTC/NOPB

ApplicationsEmbedded systems, Console/Set-Top boxesCurrent - Supply1mA
Voltage - Supply4.5 V ~ 30 VOperating Temperature-40°C ~ 125°C
Mounting TypeSurface MountPackage / Case28-TSSOP
Dc To Dc Converter TypeSynchronous Step Down ControllerNumber Of Outputs2
Pin Count28Input Voltage4.5 to 30V
Output Voltage1.3 to 30VOutput Current20A
Package TypeTSSOPMountingSurface Mount
Operating Temperature ClassificationAutomotiveOperating Temperature (min)-40C
Operating Temperature (max)125CPrimary Input Voltage30V
No. Of Outputs1No. Of Pins28
Operating Temperature Range-40°C To +125°CMslMSL 3 - 168 Hours
Control ModeCurrentRohs CompliantYes
For Use WithLM2642REVD EVAL - BOARD EVALUATION LM2642Lead Free Status / RoHS StatusLead free / RoHS Compliant
Other names*LM2642MTC
*LM2642MTC/NOPB
LM2642MTC
  
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Component Selection
Where 200nA is the maximum current drawn by FBx pin.
FIGURE 8. Output Voltage Setting
Example: Vnom=5V, Vfb=1.238V, Ifbmax=200nA.
Choose 60K
The output voltage is limited by the maximum duty cycle as
well as the minimum on time. Figure 9 shows the limits for
input and output voltages. The recommended maximum out-
put voltage is approximately 1V less than the nominal input
voltage. At 30V input, the minimum output is approximately
2.3V and the maximum is approximately 27V.
For input voltages below 5.5V, VLIN5 must be connected to
Vin through a small resistor (approximately 4.7 ohm). This
will ensure that VLIN5 does not fall below the UVLO thresh-
old.
FIGURE 9. Available Output Voltage Range
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Output Capacitor Selection
(Continued)
In applications that exhibit large and fast load current
swings, the slew rate of such a load current transient may be
beyond the response speed of the regulator. Therefore, to
meet voltage transient requirements during worst-case load
(2)
transients, special consideration should be given to output
capacitor selection. The total combined ESR of the output
capacitors must be lower than a certain value, while the total
capacitance must be greater than a certain value. Also, in
applications where the specification of output voltage regu-
lation is tight and ripple voltage must be low, starting from the
required output voltage ripple will often result in fewer design
iterations.
ALLOWED TRANSIENT VOLTAGE EXCURSION
The allowed output voltage excursion during a load transient
20046211
(∆Vc_s) is:
±
Where
±
e% is the output voltage initial accuracy.
Example: Vnom = 5V, δ% = 7%, e% = 3.4%, Vrip = 40mV
(3)
peak to peak.
(4)
Since the ripple voltage is included in the calculation of
∆Vc_s, the inductor ripple current should not be included in
the worst-case load current excursion. That is, the worst-
case load current excursion should be simply maximum load
current change specification, ∆Ic_s.
MAXIMUM ESR CALCULATION
Unless the rise and fall times of a load transient are slower
than the response speed of the control loop, if the total
combined ESR (Re) is too high, the load transient require-
ment will not be met, no matter how large the capacitance.
The maximum allowed total combined ESR is:
Example: ∆Vc_s = 160mV, ∆Ic_s = 3A. Then Re_max =
53.3mΩ.
Maximum ESR criterion can be used when the associated
capacitance is high enough, otherwise more capacitors than
the number determined by this criterion should be used in
parallel.
MINIMUM CAPACITANCE CALCULATION
In a switch mode power supply, the minimum output capaci-
tance is typically dictated by the load transient requirement.
If there is not enough capacitance, the output voltage excur-
sion will exceed the maximum allowed value even if the
maximum ESR requirement is met. The worst-case load
20046213
transient is an unloading transient that happens when the
input voltage is the highest and when the present switching
cycle has just finished. The corresponding minimum capaci-
tance is calculated as follows:
16
δ% is the output voltage regulation window and