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LTC1772B 데이터시트 PDF




Linear에서 제조한 전자 부품 LTC1772B은 전자 산업 및 응용 분야에서
광범위하게 사용되는 반도체 소자입니다.


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부품번호 LTC1772B 기능
기능 Constant Frequency Current Mode Step-Down DC/DC Controller
제조업체 Linear
로고 Linear 로고


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LTC1772B 데이터시트, 핀배열, 회로
LTC1772B
Constant Frequency
Current Mode Step-Down
DC/DC Controller in SOT-23
FEATURES
n Burst Mode® Operation Disabled for Lower Output
Ripple at Light Loads
n High Efficiency: Up to 94%
n High Output Currents Easily Achieved
n Wide VIN Range: 2.5V to 9.8V
n Constant Frequency 550kHz Operation
n Low Dropout: 100% Duty Cycle
n Output Voltage Down to 0.8V
n Current Mode Operation for Excellent Line and Load
Transient Response
n Shutdown Mode Draws Only 8µA Supply Current
n Tiny 6-Lead TSOT-23 Package
APPLICATIONS
n One or Two Lithium-Ion-Powered Applications
n Cellular Telephones
n Wireless Devices
n Portable Computers
n Distributed 3.3V, 2.5V or 1.8V Power Systems
DESCRIPTION
The LTC®1772B is a constant frequency current mode
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 270μA of quiescent current. In shut-
down, the device draws a mere 8μA.
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
TSOT-23.
For a Burst Mode operation enabled version of the
LTC1772B, please refer to the LTC1772 data sheet.
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
10k
220pF
16
ITH/RUN PGATE
LTC1772B
2
GND
3
VFB
VIN
SENSE
5
4
R1
0.03Ω
L1
M1 4.7μH
+
D1
C1
10μF
10V
C2A
47μF
6V
VIN
2.5V
TO 9.8V
VOUT
2.5V
C2B 2A
1μF
10V 174k
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
80.6k
1772 F01a
Figure 1. High Efficiency, High Output Current 2.5V/2A Regulator
Efficiency vs Load Current*
100
LTC1772
95 Burst Mode
OPERATION
90
85
80 LTC1772B
NON-Burst Mode
75 OPERATION
70
65 VIN = 3.6V
VOUT = 2.5V
60
10 100 1000 10000
LOAD CURRENT (mA)
*OUTPUT RIPPLE WAVEFORMS FOR THE CIRCUIT
OF FIGURE 1 APPEAR IN FIGURE 2.
1772 F01b
1772bfa
1




LTC1772B pdf, 반도체, 판매, 대치품
LTC1772B
TYPICAL PERFORMANCE CHARACTERISTICS
Reference Voltage
vs Temperature
825
VIN = 4.2V
820
Normalized Oscillator Frequency
vs Temperature
10
VIN = 4.2V
8
Undervoltage Lockout Trip
Voltage vs Temperature
2.24
VIN FALLING
2.20
815 6 2.16
810 4 2.12
805 2 2.08
800 0 2.04
795 –2 2.00
790 –4 1.96
785 –6 1.92
780 –8 1.88
775
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
–10
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
1.84
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
1772 G01
1772 G02
1772 G03
Maximum (VIN – SENSE) Voltage
vs Duty Cycle
120
VIN = 4.2V
110 TA = 25°C
100
90
Shutdown Threshold
vs Temperature
600
VIN = 4.2V
560
520
480
440
80 400
70 360
320
60
280
50 240
40
20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
200
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
1772 G04
1772 G05
1772bfa
4

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LTC1772B 전자부품, 판매, 대치품
LTC1772B
OPERATION (Refer to Functional Diagram)
that the external P-channel MOSFET will remain on for
more than one oscillator cycle since the inductor current
has not ramped up to the threshold set by EAMP. Further
reduction in input supply voltage will eventually cause the
P-channel MOSFET to be turned on 100%, i.e., DC. The
output voltage will then be determined by the input volt-
age minus the voltage drop across the MOSFET, the sense
resistor and the inductor.
Undervoltage Lockout
To prevent operation of the P-channel MOSFET below safe
input voltage levels, an undervoltage lockout is incorpo-
rated into the LTC1772B. When the input supply voltage
drops below approximately 2.0V, the P-channel MOSFET
and all circuitry is turned off except the undervoltage block,
which draws only several microamperes.
Short-Circuit Protection
When the output is shorted to ground, the frequency of
the oscillator will be reduced to about 120kHz. This lower
frequency allows the inductor current to safely discharge,
thereby preventing current runaway. The oscillator’s fre-
quency will gradually increase to its designed rate when
the feedback voltage again approaches 0.8V.
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’s peak current is determined by:
( )IPK
=
VITH – 0.85
10 RSENSE
when the LTC1772B is operating below 40% duty
cycle. However, once the duty cycle exceeds 40%, slope
compensation begins and effectively reduces the peak
inductor current. The amount of reduction is given by the
curves in Figure 3.
110
100
90
80
70
60
50
IRIPPLE = 0.4IPK
40 AT 5% DUTY CYCLE
30
IRIPPLE = 0.2IPK
AT 5% DUTY CYCLE
20 VIN = 4.2V
10
0 10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
1772 F03
Figure 3. Maximum Output Current vs Duty Cycle
1772bfa
7

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