LTC1876EG#TR Linear Technology, LTC1876EG#TR Datasheet - Page 14

• Manufacturer Part Number: LTC1876EG#TR
• Description: IC CTRLR/REG STEP UP/DOWN 36SSOP
• Manufacturer: Linear Technology
• Series: PolyPhase®r
• Type: Step-Down (Buck), Step-Up (Boost)r

Specifications of LTC1876EG#TR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 3
• Voltage - Output: Adj to 34V
• Current - Output: 1A
• Frequency - Switching: 140kHz ~ 340kHz
• Voltage - Input: 3.5 ~ 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: -

LTC1876
path, which could include batteries, switches, trace/con-
nector resistances and protection circuitry. Improvements
in both conducted and radiated EMI also directly accrue as
a result of the reduced RMS input current and voltage.
Of course, the improvement afforded by 2-phase opera-
tion is a function of the dual switching regulator’s relative
duty cycles which, in turn, are dependent upon the input
voltage V
the RMS input current varies for single-phase and 2-phase
operation for 3.3V and 5V regulators over a wide input
voltage range.
It can readily be seen that the advantages of 2-phase
operation are not just limited to a narrow operating range,
but in fact extend over a wide region. A good rule of thumb
for most applications is that 2-phase operation will reduce
APPLICATIO S I FOR ATIO
Figure 1 on the first page is a basic LTC1876 application
circuit. For the step-down regulators, the external compo-
nent selection is driven by the load requirement, and
begins with the selection of R
known, L can be chosen. Next, the power MOSFETs and D1
are selected. Finally, C
shown in Figure 1 can be configured for operation up to an
input voltage of 28V (limited by the external MOSFETs).
For the step-up regulator, its component selection is much
simpler. A 4.7 H or 10 H inductor that can handle at least
1A without saturating will work well with most design. A
Shottky diode is recommended and a MBR0520 from ON
Semiconductor is a very good choice.
R
R
The LTC1876 current comparator has a maximum thresh-
old of 75mV/R
SGND to 1.1(INTV
sets the peak of the inductor current, yielding a maximum
average output current I
half the peak-to-peak ripple current, I
14
OPERATIO
SENSE
SENSE
Selection For Output Current
is chosen based on the required output current.
IN
(Duty Cycle = V
SENSE
U
CC
U
and an input common mode range of
). The current comparator threshold
IN
(Refer to Functional Diagram)
and C
MAX
U
OUT
equal to the peak value less
OUT
/V
IN
SENSE
are selected . The circuit
). Figure 4 shows how
W
. Once R
L
.
U
SENSE
is
the input capacitor requirement to that for just one channel
operating at maximum current and 50% duty cycle.
Allowing a margin for variations in the LTC1876 and
external component values yields:
R
SENSE
Figure 5. FREQSET Pin Voltage vs Frequency
Figure 4. RMS Input Current Comparison
2.5
2.0
1.5
1.0
0.5
3.0
2.5
2.0
1.5
1.0
0.5
0
50
120
0
I
MAX
0
mV
V
V
O1
O2
= 5V/3A
= 3.3V/3A
OPERATING FREQUENCY (kHz)
170
10
INPUT VOLTAGE (V)
DUAL CONTROLLER
220
SINGLE PHASE
DUAL CONTROLLER
2-PHASE
20
270
30
1876 F05
1876 F04
320
40
1876fa