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PDF TD2776B Data sheet ( Hoja de datos )
| Número de pieza | TD2776B | |
| Descripción | 3A 22V Synchronous Rectified Step-Down Converter | |
| Fabricantes | Techcode | |
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Techcode®
DATASHEET
3A 22V Synchronous Rectified Step-Down Converter TD2776B
General Description
Features
The TD2776B is a monolithic synchronous buck •
regulator. The device integrates two 90mΩ •
MOSFETs, and provides 3A of continuous load current •
over a wide input voltage of 4.75V to 22V. Current •
mode control provides fast transient response •
and cycle-by-cycle current limit.
•
An adjustable soft-start prevents inrush current at •
turn-on, and in shutdown mode the supply current
drops to 1µA.
•
This device, availablein an SOP8-PP package, •
provides a very compact solution with minimal external •
components.
3A Output Current
Wide 4.75V to 22V Operating Input Range
Integrated 90mΩ Power MOSFET Switches
Output Adjustable from 0.923V to 20V
Up to 93% Efficiency
Programmable Soft-Start
Stable with Low ESR Ceramic Output Capacitors
Fixed 600KHz Frequency
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
Applications
• Distributed Power Systems
• Networking Systems
• FPGA, DSP, ASIC Power Supplies
• Green Electronics/ Appliances
• Notebook Computers
Package Types
October, 20, 2010.
Figure 1. Package Types of TD2776
Techcode Semiconductor Limited
1
SOP8
www.techcodesemi.com
1 page  
Techcode®
DATASHEET
3A 22V Synchronous Rectified Step-Down Converter TD2776B
Electrical Characteristics
VIN = 12V, Ta = 25℃ unless otherwise specified.
Parameters
Symbol
Test Condition
Shutdown Supply Current
VEN = 0V
Supply Current
Feedback Voltage
VEN = 2.0V; VFB =
1.0V
VFB 4.75V ≤ VIN ≤ 23V
Feedback Overvoltage Threshold
Error Amplifier Voltage Gain *
AEA
Error Amplifier Transconductance
GEA
∆IC = ±10µA
High-Side Switch On Resistance * RDS(ON)1
Low-Side Switch On Resistance * RDS(ON)2
High-Side Switch Leakage
Current
VEN = 0V, VSW = 0V
Upper Switch Current Limit
Minimum Duty Cycle
Lower Switch Current Limit
From Drain to Source
COMP to Current Sense
Transconductance
GCS
Oscillation Frequency
Short Circuit Oscillation
Frequency
Fosc2
VFB = 0V
Maximum Duty Cycle
DMAX
VFB = 1.0V
Minimum On Time *
EN Shutdown Threshold Voltage
VEN Rising
EN Shutdown Threshold Voltage
Hysteresis
EN Lockout Threshold Voltage
EN Lockout Hysterisis
Min.
Typ.
1
Max.
3.0
1.3 1.5
0.900 0.923 0.946
1.1
400
800
90
90
10
3.4 4.0
1.6
4.8
600
100
90
220
1.1 1.5 2.0
210
2.2 2.5 2.7
210
Unit
µA
mA
V
V
V/V
µA/V
mΩ
mΩ
µA
A
A
A/V
KHz
KHz
%
ns
V
mV
V
mV
October, 20, 2010.
Techcode Semiconductor Limited
5
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5 Page 
Techcode®
DATASHEET
3A 22V Synchronous Rectified Step-Down Converter TD2776B
Since the input capacitor (C1) absorbs the input
switching current it requires an adequate ripple current
rating. The RMS current in the input capacitor can be
estimated by:
In the case of tantalum or electrolytic capacitors,the
ESR dominates the impedance at the switching
frequency. For simplification, the output ripple can be
approximated to:
The worst-case condition occurs at VIN = 2VOUT,where
IC1 = ILOAD/2. For simplification, choose the input
capacitor whose RMS current rating greater than half
of the maximum load current.
The input capacitor can be electrolytic, tantalum or
ceramic. When using electrolytic or tantalum
capacitors, a small, high quality ceramic capacitor, i.e.
0.1μF, should be placed as close to the IC as possible.
When using ceramic capacitors, make sure that they
have enough capacitance to provide sufficient charge
to prevent excessive voltage ripple at input. The input
voltage ripple for low ESR capacitors can be
estimated by:
Where C1 is the input capacitance value.
Output Capacitor
The output capacitor is required to maintain the DC
output voltage. Ceramic, tantalum, or low ESR
electrolytic capacitors are recommended. Low ESR
capacitors are preferred to keep the output voltage
ripple low. The output voltage ripple can be estimated
by:
Where C2 is the output capacitance value and RESR is
the equivalent series resistance (ESR) value of the
output capacitor.
In the case of ceramic capacitors, the impedance at
the switching frequency is dominated by the
capacitance. The output voltage ripple is mainly
caused by the capacitance. For simplification, the
output voltage ripple can be estimated by:
The characteristics of the output capacitor also affect
the stability of the regulation system. The TD2776 can
be optimized for a wide range of capacitance and ESR
values.
Compensation Components
TD2776 employs current mode control for easy
compensation and fast transient response. The
system stability and transient response are controlled
through the COMP pin. COMP pin is the output of the
internal transconductance error amplifier. A series
capacitor-resistor combination sets a pole-zero
combination to control the characteristics of the control
system.
The DC gain of the voltage feedback loop is given by:
Where AVEA is the error amplifier voltage gain;GCS is
the current sense transconductance and RLOAD is the
load resistor value.
The system has two poles of importance. One is due
to the compensation capacitor (C3) and the output
resistor of the error amplifier, and the other is due to
the output capacitor and the load resistor. These poles
are located at:
Where GEA is the error amplifier transconductance.
October, 20, 2010.
Techcode Semiconductor Limited
11
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| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet TD2776B.PDF ] | |
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