Document
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 shutdown, 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 (%)
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
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (VIN) .........................– 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
PIN CONFIGURATION
TOP VIEW
ITH/RUN 1 GND 2 VFB 3
6 PGATE
5 VIN 4 SENSE–
S6 PACKAGE 6-LEAD PLASTIC TSOT-23
TJMAX = 150°C, θJA = 230°C/W
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC1772BES6#PBF
LTC1772BES6#TRPBF LTVU
6-Lead Plastic TSOT Package
–40°C to 85°C
LTC1772BIS6#PBF
LTC1772BIS6#TRPBF LTVU
6-Lead Plastic TSOT Package
–40°C to 85°C
LEAD BASED FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC1772BES6
LTC1772BES6#TR
LTVU
6-Lead Plastic TSOT Package
–40°C to 85°C
LTC1772BIS6
LTC1772BIS6#TR
LTVU
6-Lead Plastic TSOT Package
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 4.2V unless otherwise specified. (Note 2)
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
Input DC Supply Current Normal Operation Shutdown UVLO
Undervoltage Lockout Threshold
Typicals at VIN = 4.2V (Note 4) 2.4V ≤ VIN ≤ 9.8V, PGATE Logic High 2.4V ≤ VIN ≤ 9.8V, VITH/RUN = 0V VIN < UVLO Threshold
VIN Falling VIN Rising
270 420 8 22 6 10
l 1.55 2.00 2.35 1.85 2.10 2.40
μA μA μA
V V
Shutdown Threshold (at ITH/RUN)
l 0.15 0.35 0.55
V
Start-Up Current Source
VITH/RUN = 0V
0.25 0.5 0.85
μA
Regulated Feedback Voltage
0°C to 70°C (Note 5) –40°C to 85°C (Note 5)
l 0.780 l 0.770
0.800 0.800
0.820 0.830
V V
Output Voltage Line Regulation 2.4V ≤ VIN ≤ 9.8V (Note 5)
0.05 mV/V
Output Voltage Load Regulation ITH/RUN Sinking 5μA (Note 5) ITH/RUN Sourcing 5μA (Note 5)
2.5 mV/μA 2.5 mV/μA
1772bfa
2
LTC1772B
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
tempe.