LTC3829EFE#PBF Linear Technology, LTC3829EFE#PBF Datasheet - Page 24

• 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: -

LTC3829
applicaTions inForMaTion
The Figure 10 graph shows that the peak RMS input
current is reduced linearly, inversely proportional to the
number N of stages used. It is important to note that the
efficiency loss is proportional to the input RMS current
squared and therefore a 3-stage implementation results
in 90% less power loss when compared to a single-phase
design. Battery/input protection fuse resistance (if used),
PC board trace and connector resistance losses are also
reduced by the reduction of the input ripple current in a
PolyPhase system. The required amount of input capaci-
tance is further reduced by the factor N, due to the effective
increase in the frequency of the current pulses. Ceramic
capacitors are becoming very popular for small designs
but several cautions should be observed. X7R, X5R and
Y5V are examples of a few of the ceramic materials used
as the dielectric layer, and these different dielectrics have
very different effect on the capacitance value due to the
voltage and temperature conditions applied. Physically,
if the capacitance value changes due to applied voltage
change, there is a concommitant piezo effect which results
in radiating sound! A load that draws varying current at an
audible rate may cause an attendant varying input voltage
on a ceramic capacitor, resulting in an audible signal. A
secondary issue relates to the energy flowing back into
a ceramic capacitor whose capacitance value is being
reduced by the increasing charge. The voltage can increase

Figure 10. Normalized Input RMS Ripple Current
vs Duty Factor for One to Six Output Stages
0.6
0.5
0.4
0.3
0.2
0.1
0
0.1
0.2
0.3
DUTY FACTOR (V
0.4
1-PHASE
2-PHASE
3-PHASE
4-PHASE
6-PHASE
12-PHASE
0.5
at a considerably higher rate than the constant current being
supplied because the capacitance value is decreasing as
the voltage is increasing! Nevertheless, ceramic capacitors,
when properly selected and used, can provide the lowest
overall loss due to their extremely low ESR.
The selection of C
series resistance (ESR). Typically once the ESR requirement
is satisfied the capacitance is adequate for filtering. The
steady-state output ripple (∆V
where f = operating frequency of each stage, N is the
number of output stages, C
∆I
highest at maximum input voltage since ∆I
input voltage. The output ripple will be less than 50mV at
maximum V
and
OUT
0.6
L
C
C
∆
/V
= ripple current in each inductor. The output ripple is
OUT
OUT
V
IN
0.7
OUT
)
required ESR < N • R
>
0.8
3829 F10
≈
( )
8
IN
∆
0.9
Nf R
I
RIPPLE
with ∆I
(
1
OUT
SENSE

 
L
is driven by the required effective
ESR
= 0.4I
)
+
OUT
8
OUT(MAX)
SENSE
OUT
NfC
= output capacitance and
1
) is determined by:
OUT

 
assuming:
L
increases with
3829f