LTC3829EFE#PBF Linear Technology, LTC3829EFE#PBF Datasheet - Page 21

• Manufacturer Part Number: LTC3829EFE#PBF
• Description: IC BUCK SYNC ADJ 38TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3829EFE#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 5 V
• Frequency - Switching: 250kHz ~ 770kHz
• Voltage - Input: 4.5 ~ 38 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 38-TSSOP Exposed Pad, 38-eTSSOP, 38-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -

applicaTions inForMaTion
Slope Compensation and Inductor Peak Current
Slope compensation provides stability in constant frequen-
cy current mode architectures by preventing sub-harmonic
oscillation at high duty cycles. It is accomplished internally
by adding a compensating ramp to the inductor current
signal at duty cycles in excess of 40%. Normally, this
results in a reduction of maximum inductor peak current
for duty cycles greater than 40%. However, the LTC3829
uses a scheme that counteracts this compensating ramp,
which allows the maximum inductor peak current to remain
unaffected throughout all duty cycles.
Inductor Value Calculation and Output Ripple Current
The operating frequency and inductor selection are inter-
related in that higher operating frequencies allow the use of
smaller inductor and capacitor values. A higher frequency
generally results in lower efficiency because of MOSFET
gate charge and transition losses. In addition to this basic
trade-off, the effect of inductor value on ripple current
and low current operation must also be considered. The
PolyPhase approach reduces both input and output ripple
currents while optimizing individual output stages to run
at a lower fundamental frequency, enhancing efficiency.
The inductor value has a direct effect on ripple current.
The inductor ripple current, ∆I
L
, per individual section
Figure 8. Normalized Peak Output Current
vs Duty Factor [I
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.1
0.2
0.3
DUTY FACTOR (V
0.4
RMS
0.5
= 0.3(I
N, decreases with higher inductance or frequency and
increases with higher V
where f is the individual output stage operating frequency.
In a PolyPhase converter, the net ripple current seen by
the output capacitor is much smaller than the individual
inductor ripple currents due to the ripple cancellation. The
details on how to calculate the net output ripple current
can be found in Application Note 77.
Figure 8 shows the net ripple current seen by the output
capacitors for the different phase configurations. The
output ripple current is plotted for a fixed output voltage
as the duty factor is varied between 10% and 90% on the
x-axis. The output ripple current is normalized against the
inductor ripple current at zero duty factor. The graph can
be used in place of tedious calculations. The zero output
ripple current is obtained when:
OUT
0.6
/V
∆I
V
OP-P
IN
0.7
V
OUT
)
L
1-PHASE
2-PHASE
3-PHASE
4-PHASE
6-PHASE
12-PHASE
IN
)]
=
0.8
3829 F08
=
V
f L
OUT
N
•
k
0.9
where k

 
– 1
V
V
OUT
IN
= , ,..., –
IN
1 2

 
or V
OUT
N
:
1
LTC3829

3829f