LTC1709EG-7 Linear Technology, LTC1709EG-7 Datasheet - Page 15

• Manufacturer Part Number: LTC1709EG-7
• Description: IC SW REG STEP-DOWN SYNC 36-SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1709EG-7

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 1.3 ~ 3.5 V
• Current - Output: 3A
• Voltage - Input: 4 ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Frequency - Switching: -

APPLICATIO S I FOR ATIO
It is important to note that the efficiency loss is propor-
tional to the input RMS current squared and therefore a
2-phase implementation results in 75% 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 2-phase system.
The required amount of input capacitance is further
reduced by the factor, 2, due to the effective increase in
the frequency of the current pulses.
The selection of C
series resistance (ESR). Typically once the ESR require-
ment has been met, the RMS current rating generally far
exceeds the I
output ripple ( V
Where f = operating frequency of each stage, C
output capacitance and I
ripple currents.
The output ripple varies with input voltage since I
function of input voltage. The output ripple will be less than
50mV at max V
C
C
OUT
OUT
V
OUT
required ESR < 4(R
> 1/(16f)(R
Figure 4. Normalized RMS Input Ripple Current
vs Duty Factor for 1 and 2 Output Stages
0.6
0.5
0.4
0.3
0.2
0.1
0
0.1
RIPPLE(P-P)
I
RIPPLE
IN
0.2
OUT
with I
OUT
SENSE
U
0.3
DUTY FACTOR (V
) is determined by:
is driven by the required effective
ESR
0.4
)
requirements. The steady state
L
U
= 0.4I
1-PHASE
2-PHASE
SENSE
0.5
RIPPLE
16
OUT
0.6
fC
OUT(MAX)
) and
/V
1
IN
OUT
= combined inductor
0.7
W
)
0.8
17097 F04
/2 assuming:
0.9
U
OUT
L
is a
=
The emergence of very low ESR capacitors in small,
surface mount packages makes very physically small
implementations possible. The ability to externally com-
pensate the switching regulator loop using the I
pin(OPTI-LOOP compensation) allows a much wider se-
lection of output capacitor types. OPTI-LOOP compensa-
tion effectively removes constraints on output capacitor
ESR. The impedance characteristics of each capacitor
type are significantly different than an ideal capacitor and
therefore require accurate modeling or bench evaluation
during design.
Manufacturers such as Nichicon, United Chemicon and
Sanyo should be considered for high performance
through-hole capacitors. The OS-CON semiconductor
dielectric capacitor available from Sanyo and the Panasonic
SP surface mount types have the lowest (ESR)(size)
product of any aluminum electrolytic at a somewhat
higher price. An additional ceramic capacitor in parallel
with OS-CON type capacitors is recommended to reduce
the inductance effects.
In surface mount applications, multiple capacitors may
have to be paralleled to meet the ESR or RMS current
handling requirements of the application. Aluminum elec-
trolytic and dry tantalum capacitors are both available in
surface mount configurations. New special polymer sur-
face mount capacitors offer very low ESR also but have
much lower capacitive density per unit volume. In the case
of tantalum, it is critical that the capacitors are surge tested
for use in switching power supplies. Several excellent
choices are the AVX TPS, AVX TPSV or the KEMET T510
series of surface mount tantalums, available in case heights
ranging from 2mm to 4mm. Other capacitor types include
Sanyo OS-CON, Nichicon PL series and Sprague 595D
series. Consult the manufacturer for other specific recom-
mendations. A combination of capacitors will often result
in maximizing performance and minimizing overall cost
and size.
INTV
An internal P-channel low dropout regulator produces 5V
at the INTV
regulator powers the drivers and internal circuitry of the
LTC1709-7. The INTV
CC
Regulator
CC
pin from the V
CC
pin regulator can supply up to
IN
supply pin. The INTV
LTC1709-7
15
TH
CC