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PDF TD2778 Data sheet ( Hoja de datos )
| Número de pieza | TD2778 | |
| Descripción | 2.4A 32V Synchronous Rectified Step-Down Converter | |
| Fabricantes | Techcode | |
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Techcode®
DATASHEET
2.4A 32V Synchronous Rectified Step-Down Converter TD2778
General Description
Features
The TD2778 is a monolithic synchronous buck •
regulator. The device integrates two 90mΩ •
MOSFETs, and provides 2.4A of continuous load •
current over a wide input voltage of 4.75V to 32V. •
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.
2.4A Output Current
Wide 4.75V to 32V Operating Input Range
Integrated 90mΩ Power MOSFET Switches
Output Adjustable from 0.923V to 30V
Up to 93% Efficiency
Programmable Soft-Start
Stable with Low ESR Ceramic Output Capacitors
Fixed 200KHz
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 TD2778
Techcode Semiconductor Limited
1
SOP8
www.techcodesemi.com
1 page  
Techcode®
DATASHEET
2.4A 32V Synchronous Rectified Step-Down Converter TD2778
Electrical Characteristics
VIN = 12V, Ta = 25℃ unless otherwise specified.
Parameters
Shutdown Supply Current
Symbol
Supply Current
Feedback Voltage
VFB
Feedback Overvoltage Threshold
Error Amplifier Voltage Gain *
AEA
Error Amplifier Transconductance
GEA
High-Side Switch On Resistance * RDS(ON)1
Low-Side Switch On Resistance * RDS(ON)2
High-Side Switch Leakage
Current
Upper Switch Current Limit
Lower Switch Current Limit
COMP to Current Sense
Transconductance
GCS
Test Condition
VEN = 0V
VEN = 2.0V; VFB =
1.0V
4.75V ≤ VIN ≤30V
∆IC = ±10µA
VEN = 0V, VSW = 0V
Minimum Duty Cycle
From Drain to Source
Min.
0.900
Typ. Max.
1 3.0
1.3 1.5
0.923 0.946
1.1
400
800
90
90
10
2.9
1.1
4.8
Unit
µA
mA
V
V
V/V
µA/V
mΩ
mΩ
µA
A
A
A/V
Oscillation Frequency
Fosc1
TD2778
200 KHz
Short Circuit Oscillation
Frequency
Maximum Duty Cycle
Minimum On Time *
EN Shutdown Threshold Voltage
EN Shutdown Threshold Voltage
Hysteresis
EN Lockout Threshold Voltage
EN Lockout Hysterisis
Fosc2
DMAX
VFB = 0V
VFB = 1.0V
VEN Rising
100
90
220
1.1 1.5 2.0
KHz
%
ns
V
210
2.2 2.5 2.7
210
mV
V
mV
October, 20, 2010.
Techcode Semiconductor Limited
5
www.techcodesemi.com
5 Page 
Techcode®
DATASHEET
2.4A 32V Synchronous Rectified Step-Down Converter TD2778
The system has one zero of importance, due to the
compensation capacitor (C3) and the compensation
resistor (R3). This zero is located at:
The system may have another zero of importance, if
the output capacitor has a large capacitance and/or a
high ESR value. The zero,due to the ESR and
capacitance of the output capacitor, is located at:
Determine the C3 value by the following equation:
Where R3 is the compensation resistor.
3. Determine if the second compensation capacitor
(C6) is required. It is required if the ESR zero of the
output capacitor is located at less than half of the
switching frequency, or the following relationship is
valid:
In this case (as shown in Figure 14), a third pole set by
the compensation capacitor (C6) and the
compensation resistor (R3) is used to compensate the
effect of the ESR zero on the loop gain. This pole is
located at:
The goal of compensation design is to shape the
converter transfer function to get a desired loop gain.
The system crossover frequency where the feedback
loop has the unity gain is important. Lower crossover
frequencies result in slower line and load transient
responses,while higher crossover frequencies could
cause system instability. A good rule of thumb is to set
the crossover frequency below one-tenth of the
switching frequency.
To optimize the compensation components, the
following procedure can be used.
1. Choose the compensation resistor (R3) to set the
desired crossover frequency.
Determine the R3 value by the following equation:
If this is the case, then add the second compensation
capacitor (C6) to set the pole fP3 at the location of the
ESR zero. Determine the C6 value by the equation:
External Bootstrap Diode
An external bootstrap diode may enhance the
efficiency of the regulator, the applicable
conditions of external BST diode are:
VOUT=5V or 3.3V; and
Duty cycle is high:
In these cases, an external BST diode is
recommended from the output of the voltage regulator
to BST pin, as shown in Fig.10
Where fC is the desired crossover frequency which is
typically below one tenth of the switching frequency.
2. Choose the compensation capacitor (C3) to achieve
the desired phase margin. For applications with typical
inductor values, setting the compensation zero, fZ1,
below one-forth of the crossover frequency provides
sufficient phase margin.
Figure10.Add Optional External Bootstrap Diode to Enhance
Efficiency
The recommended external BST diode is IN4148, and
the BST cap is 0.1~1μF.
October, 20, 2010.
Techcode Semiconductor Limited
11
www.techcodesemi.com
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet TD2778.PDF ] | |
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