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PDF TJ4519 Data sheet ( Hoja de datos )
| Número de pieza | TJ4519 | |
| Descripción | 600kHz 3A Step-Down Switching Regulator | |
| Fabricantes | HTC Korea | |
| Logotipo |  |
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600kHz 3A Step-Down Switching Regulator
TJ4519
FEATURES
z Integrated 3 Amp switch
z 600kHz frequency of operation
z Current mode controller
z Precision enable threshold
z Available in SOP8-PP Package
SOP8-PP PKG
APPLICATION
z XDSL Modems
z CPE equipment
z DC-DC point of load applications
z Portable equipment
ORDERING INFORMATION
Device (Marking)
TJ4519DP
Package
SOP8-PP
DESCRIPSION
The TJ4519 is a current mode switching regulator with an integrated switch, operating at 600kHz with enable
functions. The integrated switch allows for cost effective low power solutions (peak switch current 3 amps).
High frequency of operation allows for very small passive components. Current mode operation allows for fast
dynamic response and instantaneous duty cycle adjustment as the input varies (ideal for CPE applications
where the input is a wall plug power). The low shutdown current makes it ideal for portable applications where
battery life is important.
Absolute Maximum Ratings
CHARACTERISTIC
SYMBOL
MIN.
MAX.
Input Supply Voltage
VIN -0.3 28
Boost Pin Above VSW
VBST - VSW
-
16
Boost Pin Voltage
VBST
-0.3 32
EN Pin Voltage
VEN -0.3 24
FB Pin Voltage
VFB -0.3 6
FB Pin Current
IFB - 1
Operating Ambient Temperature Range
TA -40 85
Operating Junction Temperature Range
TJ -40 150
Storage Temperature Range
TSTG
-65 150
Lead Temperature (Soldering) 5 sec
TSOL
- 260
(1) For proper operation of device, VIN should be within Max. Operating Input Voltage as defined in Electrical Characteristics.
UNIT
V
V
V
V
V
mA
℃
℃
℃
℃
Ordering Information
Order No.
Package
TJ4519DP-8L
SOP8-PP
Description
600kHz 3A Step-Down Regulator
Package Marking Supplied As
TJ4519
Reel
Jul. 2010 – Preliminary
-1-
HTC
Free Datasheet http://www.datasheet4u.com/
1 page  
600kHz 3A Step-Down Switching Regulator
TJ4519
APPLICATION INFORMATION
The TJ4519 is a current mode buck converter regulator. TJ4519 has an internal fixed-frequency clock. The
TJ4519 uses two feedback loops that control the duty cycle of the internal power switch. The error amplifier
functions like that of the voltage mode converter. The output of the error amplifier works as a switch current
reference. This technique effectively removes one of the double poles in the voltage mode system. With this, it is
much simpler to compensate a current mode converter to have better performance. The current sense amplifier in
the TJ4519 monitors the switch current during each cycle. Overcurrent protection (OCP) is triggered when the
current limit exceeds the upper limit of 3A, detected by a voltage on COMP greater than about 2V. When an OCP
fault is detected, the switch is turned off and the external COMP capacitor is quickly discharged using an internal
npn transistor. Once the COMP voltage has fallen below 250mV, an internal timer prevents any operation for 50μs,
after which the part enters a normal startup cycle. In the case of sustained overcurrent or dead-short, the part will
continually cycle through the retry sequence as described above, at a rate dependent on the value of Ccomp.
During start up, the voltage on COMP rises roughly at the rate of dv/dt=120μA/Ccomp. Ccomp is the total
capacitance value attached to COMP. Therefore, the retry time for a sustained overcurrent can be approximately
calculated as:
Tretry
=
Ccomp
•
2V
120uA
+ 50us
Figure 1 shows the voltage on COMP during a sustained overcurrent condition.
2V
250mV
Figure 1. Voltage on COMP for Startup and OCP
Enable
Pulling and holding the EN pin below 0.4V activates the shut down mode of the TJ4519 which reduces the input
supply current to less than 10uA. During the shut down mode, the switch is turned off. The TJ4519 is turned on if
the EN pin is pulled high.
Oscillator
Its internal free running oscillator sets the PWM frequency at 600 kHz for the TJ4519 without any external
components to program the frequency.
UVLO
When the EN pin is pulled and held above 1.8Vm, the voltage on Pin IN determines the operation of the TJ4519.
As VIN increases during power up, the internal circuit senses VIN and keeps the power transistor off until VIN
reaches 2.6V
Load current
The peak current IPEAK in the switch is internally limited. For a specific application, the allowed load current
ICMAX will change if the input voltage drifts away from the original design as given for continuous current mode:
Jul. 2010 – Preliminary
-5-
HTC
Free Datasheet http://www.datasheet4u.com/
5 Page 
600kHz 3A Step-Down Switching Regulator
Mag
TJ4519
Loop Gain T(s)
ωP1
ωZ
Power Stage
ωC ωP2
Figure 4. Asymptotic diagrams of power stage with current loop closed and its loop gain.
The design guidelines for the TJ4519 applications are as following:
1. Set the loop gain crossover corner frequency ωC for given switching corner frequency ωC = 2πfC
2. Place an integrator at the origin to increase DC and low frequency gains.
3. Select ωZ such that it is placed at ωP1 to obtain a -20dB/dec rate to go across the 0dB line.
4. Place a high frequency compensator pole ωP2 (ωP2 = πfs) to get the maximum attenuation of the switching
ripple and high frequency noise with the adequate phase lag at ωC.
Layout Guidelines:
In order to achieve optimal electrical and thermal performance for high frequency converters, special attention
must be paid to the PCB layouts. The goal of layout optimization is to identify the high di/dt loops and minimize
them. The following guidelines should be used to ensure proper operation of the converters.
1. A ground plane is suggested to minimize switching noises and trace losses and maximize heat transferring.
2. Start the PCB layout by placing the power components first. Arrange the power circuit to achieve a clean power
flow route. Put all power connections on one side of the PCB with wide copper filled areas if possible.
3. The VIN bypass capacitor should be placed next to the VIN and GND pins.
4. The trace connecting the feedback resistors to the output should be short, direct and far away from any noise
sources such as switching node and switching components.
5. Minimize the loop including input capacitor, the TJ4519 and freewheeling diode D2. This loop passes high di/dt
current. Make sure the trace width is wide enough to reduce copper losses in this loop. 6. Maximize the trace
width of the loop connecting the inductor, freewheeling diode D2 and the output capacitor.
7. Connect the ground of the feedback divider and the compensation components directly to the GND pin of the
TJ4519 by using a separate ground trace.
8. Connect Pin 4 to a large copper area to remove the IC heat and increase the power capability of the TJ4519. A
few feed through holes are required to connect this large copper area to a ground plane to further improve the
thermal environment of the TJ4519. The traces attached to other pins should be as wide as possible for the
same purpose.
Jul. 2010 – Preliminary
- 11 -
HTC
Free Datasheet http://www.datasheet4u.com/
11 Page | ||
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