參數(shù)資料
型號(hào)： TEA1201TS
廠商： NXP SEMICONDUCTORS
元件分類： 穩(wěn)壓器
英文描述： 0.95 V starting basic power unit
中文描述： 5 A SWITCHING REGULATOR, 720 kHz SWITCHING FREQ-MAX, PDSO16
封裝： 4.40 MM, PLASTIC, MO-152, SOT-369-1, SSOP-16
文件頁(yè)數(shù)： 7/24頁(yè)
文件大小： 108K
代理商： TEA1201TS
2002 Jun 06
7
Philips Semiconductors
Product specification
0.95 V starting basic power unit
TEA1201TS
8
FUNCTIONAL DESCRIPTION
8.1
Control mechanism
The TEA1201TS DC-to-DC converter is able to operate in
PFM (discontinuous conduction) or PWM (continuous
conduction) operating mode. All switching actions are
completely determined by a digital control circuit which
usestheoutputvoltagelevelasitscontrolinput.Thisnovel
digital approach enables the use of a new pulse width and
frequency modulation scheme, which ensures optimum
power efficiency over the complete range of operation of
the converter.
When high output power is requested, the device will
operate in PWM (continuous conduction) operating mode.
This results in minimum AC currents in the circuit
components and hence optimum efficiency, minimum
costs and low EMC. In this operating mode, the output
voltage is allowed to vary between two predefined voltage
levels. As long as the output voltage stays within this
so-called window, switching continues in a fixed pattern.
When the output voltage reaches one of the window
borders, the digital controller immediately reacts by
adjusting the pulse width and inserting a current step in
such a way that the output voltage stays within the window
with higher or lower current capability. This approach
enables very fast reaction to load variations. Figure 3
shows the response of the converter to a sudden load
increase. The upper trace shows the output voltage.
The ripple on top of the DC level is a result of the current
in the output capacitor, which changes in sign twice per
cycle, times the internal Equivalent Series Resistance
(ESR) of the capacitor. After each ramp-down of the
inductor current, i.e. when the ESR effect increases the
output voltage, the converter determines what to do in the
next cycle. As soon as more load current is taken from the
output the output voltage starts to decay.
When the output voltage becomes lower than the low limit
of the window, a corrective action is taken by a ramp-up of
the inductor current during a much longer time. As a result,
the DC current level is increased and normal PWM control
can continue. The output voltage (including ESR effect) is
again within the predefined window.
Figure 4 shows the spread of the output voltage window.
The absolute value is mostly dependent on spread, while
the actual window size (V
wdw(high)
V
wdw(low)
) is not
affected. For one specific device, the output voltage will
not vary more than 2% (typical value).
In low output power situations, the TEA1201TS will switch
over to PFM (discontinuous conduction) operating mode.
In this mode, regulation information from an earlier PWM
operating mode is used. This results in optimum inductor
peak current levels in the PFM mode, which are slightly
larger than the inductor ripple current in the PWM mode.
As a result, the transition between PFM and PWM mode is
optimum under all circumstances. In the PFM mode the
TEA1201TS regulates the output voltage to the high
window limit as shown in Fig.3.
8.2
Synchronous rectification
For optimum efficiency over the whole load range,
synchronous rectifiers inside the TEA1201TS ensure that
during the whole second switching phase, all inductor
current will flow through the low-ohmic power MOSFETs.
Special circuitry is included which detects when the
inductorcurrentreacheszero.Followingthisdetection,the
digital controller switches off the power MOSFET and
proceeds with regulation.
8.3
Start-up
Start-up from low input voltage in the boost mode is
realized by an independent start-up oscillator, which starts
switching the N-type power MOSFET as soon as the
low-battery detector detects a sufficiently high voltage.
The inductor current is limited internally to ensure
soft-starting. The switch actions of the start-up oscillator
will increase the output voltage. As soon as the output
voltage is high enough for normal regulation, the digital
control system takes control over the power MOSFETs.
8.4
Undervoltage lockout
As a result of too high a load or disconnection of the input
power source, the output voltage can drop so low that
normal regulation cannot be guaranteed. In this event, the
device switches back to start-up mode. If the output
voltage drops even further, switching is stopped
completely.
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