LT1777CS#PBF Linear Technology, LT1777CS#PBF Datasheet

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LT1777CS#PBF

Manufacturer Part Number
LT1777CS#PBF
Description
IC SWREG STP-DWN LOWNOISE 16SOIC
Manufacturer
Linear Technology
Type
Step-Down (Buck)r
Datasheet

Specifications of LT1777CS#PBF

Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
1.24 ~ 30 V
Current - Output
700mA
Frequency - Switching
100kHz
Voltage - Input
12 ~ 48 V
Operating Temperature
0°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
16-SOIC (3.9mm Width)
Primary Input Voltage
48V
No. Of Outputs
1
Output Voltage
40.8V
Output Current
1A
No. Of Pins
16
Operating Temperature Range
0°C To +125°C
Msl
MSL 1 - Unlimited
Rohs Compliant
Yes
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Power - Output
-

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Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
LT1777CS#PBFLT1777CS
Manufacturer:
LINEAR/凌特
Quantity:
20 000
Company:
Part Number:
LT1777CS#PBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
Company:
Part Number:
LT1777CS#PBFLT1777CS#TRPBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
FEATURES
TYPICAL APPLICATIO
APPLICATIO S
24V
V
IN
Programmable dI/dt Limit
Internally Limited dV/dt
High Input Voltage: 48V Max
700mA Peak Switch Rating
True Current Mode Control
100kHz Fixed Operating Frequency
Synchronizable to 250kHz
Low Supply Current in Shutdown: 30 A
Low Thermal Resistance 16-Pin SO Package
Automotive Cellular and GPS Receivers
Telecom Power Supplies
Industrial Instrument Power Supplies
*PROGRAMS dI/dT
+
100pF
39 F
63V
2200pF
12k
100pF
12
14
U
3
Low Noise 5V Step-Down Supply
SHDN
SYNC
V
C
LT1777
SGND
V
IN
10
7
V
V
SW
V
CC
FB
D
4
6
5
13
U
1 H*
MBRS1100
220 H
+
100 F
10V
DESCRIPTIO
The LT
noise sensitive applications. It contains a dI/dt limiting
circuit programmed via a small external inductor in the
switching path. Internal circuitry also generates controlled
dV/dt ramp rates.
The monolithic die includes all oscillator, control and
protection circuitry. The part can accept operating input
voltages as high as 48V, and contains an output switch
rated at 700mA peak current. Current mode control offers
excellent dynamic input supply rejection and short-circuit
protection. The internal control circuitry is normally pow-
ered via the V
directly from the V
tion). The fused-lead SO16 package and 100kHz switch-
ing frequency allow for minimal PC board area
requirements.
36.5k
1%
12.1k
1%
1777 TA01
, LTC and LT are registered trademarks of Linear Technology Corporation.
V
5V
400mA
OUT
®
1777 is a Buck (step-down) regulator designed for
Low Noise Step-Down
200mA/DIV
Switching Regulator
CURRENT
CC
VOLTAGE
10V/DIV
pin, thereby minimizing power drawn
V
V
SW
SW
IN
U
supply (see Applications Informa-
V
SW
Switching Waveforms
500ns/DIV
LT1777
1
1777 TA02

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LT1777CS#PBF Summary of contents

Page 1

... The internal control circuitry is normally pow- ered via the V directly from the V tion). The fused-lead SO16 package and 100kHz switch- ing frequency allow for minimal PC board area requirements. , LTC and LT are registered trademarks of Linear Technology Corporation 220 H V OUT 5V + ...

Page 2

LT1777 ABSOLUTE MAXIMUM (Note 1) Supply Voltage ....................................................... 48V Switch Voltage (V – (Note 4) ...................... 51V IN SW SHDN, SYNC Pin Voltage .......................................... 7V V Pin Voltage ...................................................... 30V CC FB Pin Voltage ........................................................ ...

Page 3

ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are 24V, V Open 5V 1.4V unless otherwise noted SYMBOL PARAMETER Output Switch ...

Page 4

LT1777 W U TYPICAL PERFOR A CE CHARACTERISTICS Minimum Input Voltage vs Temperature 7.4 7.2 7.0 6.8 6.6 6.4 6.2 6.0 –50 – TEMPERATURE ( C) Switch Current Limit vs Duty Cycle 1000 ...

Page 5

W U TYPICAL PERFOR A CE CHARACTERISTICS Switching Frequency vs Temperature 106 104 102 100 –50 – TEMPERATURE ( C) Output dI/dt Sense Voltage vs Temperature 2.0 1.8 1.6 1.4 1.2 1.0 0.8 ...

Page 6

LT1777 PIN FUNCTIONS GND (Pins 16): These corner package pins are mechanically connected to the die paddle and thus aid in conducting away internally generated heat. As these are electrically connected to the die ...

Page 7

W BLOCK DIAGRA SHDN 3 BIAS SYNC 12 OSC SGND OUTPUT STAGE SI PLIFIED SCHE ATIC ...

Page 8

LT1777 U OPERATIO The LT1777 is a current mode step-down switcher regu- lator IC designed for low noise operation. The Block Diagram shows an overall view of the system. The indi- vidual blocks are straightforward and similar to those found ...

Page 9

U U APPLICATIONS INFORMATION Basics of Low Noise Operation Switching power supply circuits are often preferred over linear topologies for their improved efficiency (P However, their typically rapid voltage and current slew rates often cause “radio frequency” interference prob- lems, ...

Page 10

LT1777 U U APPLICATIONS INFORMATION Deciding upon a value for the sense inductor involves evaluating the trade-off between overall efficiency ( and switch current slew rate. Larger sense inductors IN yield lower current slew rates which offer reduced ...

Page 11

U U APPLICATIONS INFORMATION current waveform. The four sense inductor values 0. and 2.2 H yield dI/dt rates of roughly 4.5A/ s, 2.2A/ s, 1.4A/ s and 0.6A/ s, respectively. These photos show that ...

Page 12

LT1777 U U APPLICATIONS INFORMATION 0MHz to 20MHz (2MHz/DIV) (a) LT1676 for Comparison 0MHz to 20MHz (2MHz/DIV) (b) LT1777 with L SENSE 0MHz to 20MHz (2MHz/DIV) (c) LT1777 with L SENSE Figure 4. Spectral Analysis of Current Waveforms in Figures ...

Page 13

U U APPLICATIONS INFORMATION GND 500ns/DIV Figure 6. LT1676 V Node Voltage Behavior SW for Comparison Purposes Only, V Selecting Main Inductor There are several parameters to consider when selecting a main inductor. These include inductance value, peak current rating ...

Page 14

LT1777 U U APPLICATIONS INFORMATION tors. Their relatively low ESR in the mid-MHz region can further attenuate high speed glitches. Maximum Load/Short-Circuit Considerations The LT1777 is a current mode controller. It uses the V node voltage as an input to ...

Page 15

U U APPLICATIONS INFORMATION However, remember that oscillator slowdown to achieve short-circuit protection (discussed above) is dependent on FB pin behavior, and this in turn, is sensitive to FB node external impedance. The graph in Figure 7 shows the typical ...

Page 16

LT1777 U U APPLICATIONS INFORMATION As an example, assume that the capacitance between the V node and a high impedance pin node is 0.1pF, and that SW the high impedance node in question exhibits a capaci- tance of 1pF to ...

Page 17

U TYPICAL APPLICATIONS Basic 5V Output Application Figure 8 shows a basic application that produces 500mA I . Efficiency and Internal Power Dissipation OUT graphs are shown in Figure 9 for input voltages of 12V, 24V ...

Page 18

LT1777 U TYPICAL APPLICATIONS Efficiency 12V OUT 12V (mA) LOAD 24V IN ...

Page 19

U TYPICAL APPLICATIONS Basic 3.3V Output Application Figure 10 shows a circuit similar to the previous example, but modified for a 3.3V output. Once again, Efficiency and Internal Power Dissipation graphs are shown in Figure 11 for input voltages of ...

Page 20

LT1777 U TYPICAL APPLICATIONS Efficiency 12V 3.3V OUT 12V (mA) LOAD 24V IN ...

Page 21

U TYPICAL APPLICATIONS Optional Input/Output Filtering When minimum conducted noise is required often advantageous to add an explicit input and/or output filter to the topology. This can be a cost-effective way to reduce conducted noise on the input ...

Page 22

LT1777 U TYPICAL APPLICATIONS V NODE OUT AC COUPLED 2mV/DIV 2 s/DIV (a) Before Output Filter User Programmable Undervoltage Lockout Figure 15 uses a resistor divider between V to drive the SHDN node. This is a simple, cost-effective way to ...

Page 23

... FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 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 24

... Fixed Frequency 550kHz Operation, MSOP Package 200kHz Operation, V value, but this will overheat the inductor. L2 200 H V OUT 100 F 36.5k D1 0.1 F 10V 1% R2 12.1k 1% 1777 TA03 Up to 46V IN from 3.5V to 36V, SO-8 Package IN 1777f LT/TP 0899 4K • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1999 ...

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