ltc1772b Linear Technology Corporation, ltc1772b Datasheet

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ltc1772b

Manufacturer Part Number
ltc1772b
Description
Constant Frequency Current Mode Step-down Dc/dc Controller In Sot-23
Manufacturer
Linear Technology Corporation
Datasheet

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FEATURES
APPLICATIO S
TYPICAL
Burst Mode
Ripple at Light Loads
High Efficiency: Up to 94%
High Output Currents Easily Achieved
Wide V
Constant Frequency 550kHz Operation
Low Dropout: 100% Duty Cycle
Output Voltage down to 0.8V
Current Mode Operation for Excellent Line and Load
Transient Response
Shutdown Mode Draws Only 8 A Supply Current
Tiny 6-Lead SOT-23 Package
One or Two Lithium-Ion-Powered Applications
Cellular Telephones
Wireless Devices
Portable Computers
Distributed 3.3V, 2.5V or 1.8V Power Systems
C1: TAIYO YUDEN LMK325BJ106K-T
C2A: SANYO 6TPA47M
C2B: AVX 0805ZC105KAT1A
D1: MOTOROLA MBRM120T3
L1: MURATA LQN6C-4R7
M1: FAIRCHILD FDC638P
R1: IRC LRC-LR1206-01-R030F
10k
220pF
Figure 1. High Efficiency, High Output Current 2.5V/2A Regulator
IN
Range: 2.5V to 9.8V
APPLICATION
TM
1
2
3
Operation Disabled for Lower Output
I
GND
V
TH
FB
U
/RUN
LTC1772B
SENSE
PGATE
V
IN
6
5
4
U
R1
0.03
M1
D1
4.7 H
L1
+
C1
10 F
10V
C2A
47 F
6V
DC/DC Controller in SOT-23
C2B
1 F
10V
DESCRIPTIO
The LTC
step-down DC/DC controller providing excellent AC and
DC load and line regulation. The device incorporates an
accurate undervoltage lockout feature that shuts down the
LTC1772B when the input voltage falls below 2.0V.
The LTC1772B provides a 2.5% output voltage accuracy
and consumes only 270 A of quiescent current. In shut-
down, the device draws a mere 8 A.
To further maximize the life of a battery source, the
external P-channel MOSFET is turned on continuously in
dropout (100% duty cycle). High constant operating
frequency of 550kHz allows the use of a small external
inductor.
The LTC1772B is available in a small footprint 6-lead
SOT-23.
For a Burst Mode operation enabled version of the
LTC1772B, please refer to the LTC1772 data sheet.
Burst Mode is a trademark of Linear Technology Corporation.
Current Mode Step-Down
, LTC and LT are registered trademarks of Linear Technology Corporation.
174k
80.6k
V
2.5V
TO 9.8V
V
2.5V
2A
IN
OUT
1772 F01a
®
1772B is a constant frequency current mode
Constant Frequency
100
U
95
90
85
80
75
70
65
60
*OUTPUT RIPPLE WAVEFORMS FOR THE CIRCUIT
OF FIGURE 1 APPEAR IN FIGURE 2.
LTC1772
BURST MODE
OPERATION
Efficiency vs Load Current*
10
LOAD CURRENT (mA)
LTC1772B
NON-BURST MODE
OPERATION
100
LTC1772B
1000
V
V
IN
OUT
= 3.6V
= 2.5V
1772 F01b
10000
1

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ltc1772b Summary of contents

Page 1

... P-channel MOSFET is turned on continuously in dropout (100% duty cycle). High constant operating frequency of 550kHz allows the use of a small external inductor. The LTC1772B is available in a small footprint 6-lead SOT-23. For a Burst Mode operation enabled version of the LTC1772B, please refer to the LTC1772 data sheet. ...

Page 2

... J A Note 4: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. Note 5: The LTC1772B is tested in a feedback loop that servos V output of the error amplifier. Note 6: Peak current sense voltage is reduced dependent on duty cycle to and power a percentage of value as given in Figure 2. ...

Page 3

... G04 – SENSE (Pin 4): The Negative Input to the Current Com- parator. V (Pin 5): Supply Pin. Must be closely decoupled to GND IN Pin 2. PGATE (Pin 6): Gate Drive for the External P-Channel MOSFET. This pin swings from LTC1772B Undervoltage Lockout Trip Voltage vs Temperature 2.24 V FALLING IN 2.20 2.16 2.12 2.08 2 ...

Page 4

... U OPERATIO (Refer to Functional Diagram) Main Control Loop The LTC1772B is a constant frequency current mode switching regulator. During normal operation, the external P-channel power MOSFET is turned on each cycle when the oscillator sets the RS latch (RS1) and turned off when the current comparator (ICMP) resets the latch. The peak ...

Page 5

... At lower output current levels, the improve- P-P ment is even greater. This comes at a tradeoff of lower efficiency for the non-Burst Mode operation part (see Figure 1). Also notice the constant frequency operation of the LTC1772B, even maximum output current. V Ripple for Figure 1 Circuit Using OUT LTC1772 Burst Mode Operation. ...

Page 6

... OPERATIO (Refer to Functional Diagram) Overvoltage Protection As a further protection, the overvoltage comparator in the LTC1772B will turn the external MOSFET off when the feedback voltage has risen 7.5% above the reference voltage of 0.8V. This comparator has a typical hysteresis of 20mV. Slope Compensation and Inductor’s Peak Current The inductor’ ...

Page 7

... MOSFET (R guaranteed 2.5V) is required for applications that GS work close to this voltage. When these MOSFETs are used, make sure that the input supply to the LTC1772B is less than the absolute maximum V rating, typically 8V. GS The required minimum R of the MOSFET is gov- DS(ON) erned by its allowable power dissipation ...

Page 8

... RMS current rating generally far exceeds the RIPPLE(P-P) OUT D Low Supply Operation Although the LTC1772B can function down to approxi OUT mately 2.0V, the maximum allowable output current is V reduced when V IN amount of change as the supply is reduced down to 2V. ...

Page 9

... Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC1772B circuits: 1) LTC1772B DC bias cur- rent, 2) MOSFET gate charge current voltage drop of the output diode ...

Page 10

... When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the R ITH C ITH BOLD LINES INDICATE HIGH CURRENT PATHS Figure 7. LTC1772B Layout Diagram (See PC Board Layout Checklist LTC1772B. These items are illustrated graphically in the layout diagram in Figure 7. Check the following in your layout: 1 ...

Page 11

... U TYPICAL APPLICATIO S LTC1772B High Efficiency, Small Footprint 3.3V to 1.8V/0.5A Regulator R4 10k C3 220pF R4 10k C3 220pF C1: TAIYO YUDEN CERAMIC LMK325BJ106K-T C2: AVXTPSE107M010R0100 D1: IR10BQ015 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. ...

Page 12

... DC/DC Controller in SOT-23 LTC1773 95% Efficient Synchronous Step-Down Controller LTC1872 SOT-23 Step-Up Controller trademark of Linear Technology Corporation. SENSE Linear Technology Corporation 12 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear-tech.com LTC1772B 3.3V to 5V/1A Boost Regulator R1 0.033 4.7 H 16V 2 D1 ...

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