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参数资料
| 型号： | PTV03020WAH |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 电源模块 |
| 英文描述： | 1-OUTPUT DC-DC REG PWR SUPPLY MODULE |
| 封装： | SIP-12 |
| 文件页数： | 5/19页 |
| 文件大小： | 434K |
| 代理商： | PTV03020WAH |
www.ti.com
SLTS243A – FEBRUARY 2005 – REVISED OCTOBER 2007
volt-for-volt basis. By connecting the Track pin of a number of these modules together, the output voltages follow
a common signal during power up and power down. The control signal can be an externally generated master
ramp waveform, or the output voltage from another power supply circuit (3). For convenience, the Track input
incorporates an internal RC-charge circuit. This operates off the module input voltage to produce a suitable rising
waveform at power up.
Typical Application
The basic implementation of Auto-Track allows for simultaneous voltage sequencing of a number of Auto-Track
compliant modules. Connecting the Track inputs of two or more modules forces their track input to follow the
same collective RC-ramp waveform, and allows their power-up sequence to be coordinated from a common track
control signal. This can be an open-collector (or open drain) device, such as a power-up reset voltage supervisor
IC. See U3 in Figure 11.
To coordinate a power-up sequence, the Track control must first be pulled to ground potential. This should be
done at or before input power is applied to the modules. The ground signal should be maintained for at least
20 ms after input power has been applied. This brief period gives the modules time to complete their internal
soft-start initialization (4), enabling them to produce an output voltage. A low-cost supply voltage supervisor IC,
with a built-in time delay, is an ideal component for automatically controlling the track inputs at power up.
Figure 11 shows how the TPS3808G33 supply voltage supervisor IC (U3) can be used to coordinate the
sequenced power-up of two 3.3-V input Auto-Track modules. The output of the TPS3808G33 supervisor
becomes active above an input voltage of 0.8 V, enabling it to assert a ground signal to the common track
control well before the input voltage has reached the module's undervoltage lockout threshold. The ground signal
is maintained until approximately 27 ms after the input voltage has risen above U3's voltage threshold, which is
3.07 V. The 27-ms time period is controlled by the capacitor C3. The value of 4700 pF provides sufficient time
delay for the modules to complete their internal soft-start initialization. The output voltage of each module
remains at zero until the track control voltage is allowed to rise. When U3 removes the ground signal, the track
control voltage automatically rises. This causes the output voltage of each module to rise simultaneously with the
other modules, until each reaches its respective set-point voltage.
Figure 12 shows the output voltage waveforms from the circuit of Figure 11 after input voltage is applied to the
circuit. The waveforms, VO1 and VO2 represent the output voltages from the two power modules, U1 (2.5 V) and
U2 (1.2 V), respectively. VTRK, VO1, and VO2 are shown rising together to produce the desired simultaneous
power-up characteristic.
The same circuit also provides a power-down sequence. When the input voltage falls below U3's voltage
threshold, the ground signal is reapplied to the common track control. This pulls the track inputs to zero volts,
forcing the output of each module to follow, as shown in Figure 13. In order for a simultaneous power-down to
occur, the track inputs must be pulled low before the input voltage has fallen below the modules' undervoltage
lockout. This is an important constraint. Once the modules recognize that a valid input voltage is no longer
present, their outputs can no longer follow the voltage applied at their track input. During a power-down
sequence, the fall in the output voltage from the modules is limited by the maximum output capacitance and the
Auto-Track slew rate. If the Track pin is pulled low at a slew rate greater than 1 V/ms, the discharge of the output
capacitors will induce large currents which could exceed the peak current rating of the module. This will result in
a reduction in the maximum allowable output capacitance as listed in the Electrical Characteristics table. When
controlling the Track pin of the PTV03020W using a voltage supervisor IC, the slew rate is increased, therefore
COmax is reduced to 6600F.
Notes on Use of Auto-Track
1. The Auto-Track function tracks almost any voltage ramp during power up, and is compatible with ramp
speeds of up to 1 V/ms.
2. The Track pin voltage must be allowed to rise above the module set-point voltage before the module
regulates at its adjusted set-point voltage.
3. The absolute maximum voltage that may be applied to the Track pin is the input voltage VI.
4. The module cannot follow a voltage at its track control input until it has completed its soft-start initialization.
This takes about 20 ms from the time that a valid voltage has been applied to its input. During this period, it
is recommended that the Track pin be held at ground potential.
5. The Auto-Track function is disabled by connecting the Track pin to the input voltage (VI). When Auto-Track is
disabled, the output voltage rises at a quicker and more linear rate after input power has been applied.
Copyright 2005–2007, Texas Instruments Incorporated
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Product Folder Link(s) :PTV03020W
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