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Linear Technology Electronic Components Datasheet

LTC1874 Datasheet

Dual Constant Frequency Current Mode Step-Down DC/DC Controller

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LTC1874 pdf
LTC1874
Dual Constant Frequency
Current Mode Step-Down
DC/DC Controller
FEATURES
s High Efficiency: Up to 94%
s High Output Currents Easily Achieved
s Wide VIN Range: 2.5V to 9.8V
s Constant Frequency 550kHz Operation
s Burst ModeTM Operation at Light Load
s Low Dropout: 100% Duty Cycle
s 0.8V Reference Allows Low Output Voltages
s Current Mode Operation for Excellent
Line and Load Transient Response
s Low Quiescent Current: 270µA (Each Controller)
s Separate Shutdown Pin for Each Controller
s Shutdown Mode Draws Only
8µA Supply Current (Each Controller)
s ±2.5% Reference Accuracy
s Available in 16-Lead Narrow SSOP
s Each Controller Functions Independent of the Other
U
APPLICATIO S
s 1- or 2-Cell Lithium-Ion-Powered Applications
s Personal Information Appliances
s Portable Computers
s Distributed 3.3V, 2.5V or 1.8V Power Systems
DESCRIPTIO
The LTC®1874 is a dual constant frequency current mode
step-down DC/DC controller with excellent AC and DC load
and line regulation. Each controller has an accurate
undervoltage lockout that shuts down the individual con-
troller when the input voltage falls below 2.0V.
The LTC1874 boasts ±2.5% output voltage accuracy and
consumes only 270µA of quiescent current per controller.
The LTC1874 is configured with Burst Mode operation,
which enhances efficiency at low output current for appli-
cations where efficiency is a prime consideration.
To further maximize the life of a battery source, each
external P-channel MOSFET is turned on continuously in
dropout (100% duty cycle). In shutdown, each controller
draws a mere 8µA. High constant operating frequency of
550kHz allows the use of small external inductors.
The LTC1874 is available in a small footprint 16-lead
narrow SSOP.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
VIN
3.5V
TO 9.5V
CIN
10µF
16V
×2
R1
0.04
VOUT1
3.3V
1A
L1 M1
4.7µH
+
C1
47µF
D1
C1, C2: SANYO POSCAP 6TPA47M
CIN: TAIYO YUDEN CERAMIC
EMK325BJ106MNT (× 2)
249k
6V
D1, D2: MBRM120
L1, L2: COILCRAFT D01608C-472
80.6k
M1, M2: Si3443DV
R1, R2: DALE 0.25W
10k
220pF
1 LTC1874 8
VIN1 PVIN2
2 SENSE1
7
PGATE2
3
GND1
6
PGND2
4
VFB1
5
ITH/RUN2
13
ITH/RUN1
12
VFB2
14
PGND1
11
GND2
15
PGATE1
SENSE210
16
PVIN1
9
VIN2
10k
220pF
R2
0.04
M2 L2
4.7µH
+
D2
Figure 1. LTC1874 3.5V-9.5V Input to 3.3V/1A and 1.8V/1A Dual Step-Down Converter
C2
47µF
6V
VOUT2
1.8V
1A
100k
80.6k
1874 TA01
1


Linear Technology Electronic Components Datasheet

LTC1874 Datasheet

Dual Constant Frequency Current Mode Step-Down DC/DC Controller

No Preview Available !

LTC1874 pdf
LTC1874
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (VIN, PVIN) ...............– 0.3V to 10V
SENSE , PGATE Voltages ............. – 0.3V to (VIN + 0.3V)
VFB, ITH/RUN Voltages ..............................– 0.3V to 2.4V
PGATE Peak Output Current (< 10µs) ....................... 1A
Storage Ambient Temperature Range ... – 65°C to 150°C
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Junction Temperature (Note 3) ............................. 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
PACKAGE/ORDER INFORMATION
VIN1 1
SENSE12
GND1 3
TOP VIEW
16 PVIN1
15 PGATE1
14 PGND1
ORDER PART
NUMBER
LTC1874EGN
VFB1
ITH/RUN2
PGND2
4
5
6
PGATE2 7
13 ITH/RUN1
12 VFB2
11 GND2
10 SENSE2
GN PART MARKING
PVIN2 8
9 VIN2
GN PACKAGE
16-LEAD NARROW PLASTIC SSOP
TJMAX = 150°C, θJA = 135°C/ W
1874
Consult factory for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS All specifications apply to each controller. The q denotes specifications that
apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 4.2V unless otherwise specified.
(Note 2)
PARAMETER
Input DC Supply Current (Per Controller)
Normal Operation
Sleep Mode
Shutdown
UVLO
Undervoltage Lockout Threshold
Shutdown Threshold (at ITH/RUN)
Start-Up Current Source
Regulated Feedback Voltage
Output Voltage Line Regulation
Output Voltage Load Regulation
VFB Input Current
Overvoltage Protect Threshold
Overvoltage Protect Hysteresis
Oscillator Frequency
Gate Drive Rise Time
Gate Drive Fall Time
Peak Current Sense Voltage
CONDITIONS
Typicals at VIN = 4.2V (Note 4)
2.4V VIN 9.8V
2.4V VIN 9.8V
2.4V VIN 9.8V, VITH/RUN = 0V
VIN < UVLO Threshold
VIN Falling
VIN Rising
VITH/RUN = 0V
TA = 0°C to 70°C (Note 5)
TA = – 40°C to 85°C (Note 5)
2.4V VIN 9.8V (Note 5)
ITH/RUN Sinking 5µA (Note 5)
ITH/RUN Sourcing 5µA (Note 5)
(Note 5)
Measured at VFB
VFB = 0.8V
VFB = 0V
CLOAD = 3000pF
CLOAD = 3000pF
(Note 6)
MIN TYP MAX
q 1.55
1.85
q 0.15
0.25
q 0.780
q 0.770
0.820
500
270
230
8
6
2.0
2.3
0.35
0.5
0.800
0.800
0.05
2.5
2.5
10
0.860
20
550
120
40
40
120
420
370
22
10
2.35
2.40
0.55
0.85
0.820
0.830
50
0.895
650
UNITS
µA
µA
µA
µA
V
V
V
µA
V
V
mV/V
mV/µA
mV/µA
nA
V
mV
kHz
kHz
ns
ns
mV
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC1874E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: TJ is calculated from the ambient temperature TA and power
dissipation PD according to the following formula:
TJ = TA + (PD θJA°C/W)
Note 4: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 5: Each controller in the LTC1874 is individually tested in a feedback
loop that servos VFB to the output of the error amplifier.
Note 6: Peak current sense voltage is reduced dependent upon duty cycle
to a percentage of value as given in Figure 2.
2


Part Number LTC1874
Description Dual Constant Frequency Current Mode Step-Down DC/DC Controller
Maker Linear Technology
Total Page 12 Pages
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