参数资料
型号: TPS62351YZG
厂商: TEXAS INSTRUMENTS INC
元件分类: 稳压器
英文描述: 1.6 A SWITCHING REGULATOR, 3350 kHz SWITCHING FREQ-MAX, BGA12
封装: DSBGA-12
文件页数: 16/46页
文件大小: 1530K
代理商: TPS62351YZG
Power-Save Mode : Light PFM
Mode Selection and Frequency Synchronization
Soft Start
www.ti.com .............................................................................................................................................................. SLVS540E – MAY 2006 – REVISED APRIL 2008
With decreasing load current, the device can also automatically switch into light PFM pulse skipping operation in
which the power stage operates intermittently based on load demand. The advantage of the light PFM is much
lower IQ (28 A) and drastically higher efficiency compared with fast PFM in low output loads.
In light PFM mode, the converter only operates when the output voltage trips below a set threshold voltage
(VOnominal). It ramps up the output voltage with one or several pulses and goes back into power-save mode. As
a consequence in power-save mode the average output voltage is slightly higher than its nominal value in PWM
mode.
In order to get a proper transition between light PFM and PWM operation, the output voltage ripple (in light PFM
mode) has been made proportional to the input voltage. It is possible to reduce the output voltage ripple by
setting the LIGHTPFM OPTIMIZE (VSEL0[6] or VSEL1[6]) bit low. However, this is only practical in applications
operating with a 1-
H (typical) inductor, with a load current less than V
I / 25 and which do not require the
auto-mode transition function.
When operating with a 2.2-
H (typical) inductor, the LIGHTPFM OPTIMIZE (VSEL0[6] or VSEL1[6]) bit should
always be set to low. In this case, the auto-mode transition is fully functional without any restriction on the load
current.
The TPS6235x can be synchronized to an external clock signal by the SYNC pin. Pulling the SYNC pin to a
static state high or low state has no effect on the converter's operation.
Depending on the settings of CONTROL1 register the device can be operated in either the fixed frequency PWM
mode or in the automatic PWM and power-save mode. In this mode, the converter operates in fixed frequency
PWM mode at moderate to heavy loads and in the PFM mode during light loads, which maintains high efficiency
over a wide load current range. For more details, see the CONTROL1 register description.
The fixed frequency PWM mode has the tightest regulation and the best line/load transient performance.
Furthermore, this mode of operation allows simple filtering of the switching frequency for noise-sensitive
applications. In fixed frequency PWM mode, the efficiency is lower compared to the power-save mode during
light loads. It is possible to switch from power-save mode (light or fast PWM) to forced PWM mode during
operation either via the VSEL signal or by re-programming the CONTROL1 register. This allows adjustments to
the converters operation to match the specific system requirements leading to more efficient and flexible power
management.
When the synchronization is enabled (CONTROL2[5]=1), the mode is set to fixed-frequency operation and the
P-channel MOSFET turn on is synchronized to the falling edge of the external clock. This creates the ability for
multiple converters to be connected together in a master-slave configuration for frequency matching of the
converters (see the application section for more details).
When CONTROL1[1:0]=00 and VSEL signal is low, the converter operates according to MODE0 bit and the
synchronization is disabled regardless of EN_SYNC and HW_nSW bits.
The TPS6235x has an internal soft-start circuit that limits the inrush current during start-up. This prevents
possible input voltage drops when a battery or a high-impedance power source is connected to the input of the
converter.
In the TPS62350/1/2/3/4/5 devices, the soft start is implemented as a digital circuit increasing the switch current
in steps of typically 350 mA, 675 mA, 1000 mA, and the typical switch current limit of 1350 mA. The current limit
transitions to the next step every 256 clocks (
≈ 88s). To be able to switch from 675 mA to 1000 mA current limit
step, the output voltage needs to be higher than 0.5 x VO(NOM) (otherwise the parts keeps operating at 675 mA
current limit).
In the TPS62356 device, the soft start is implemented as a digital circuit increasing the switch current in steps of
typically 400 mA, 775 mA, 1150 mA, and the typical switch current limit of 1550 mA. The current limit transitions
to the next step every 256 clocks (
≈ 88s). To switch from 775 mA to 1150 mA current limit step, the output
voltage needs to be higher than 0.5 x VO(NOM) (otherwise the parts keeps operating at 775 mA current limit).
Copyright 2006–2008, Texas Instruments Incorporated
23
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