参数资料
型号: TPS62122DRVT
厂商: TEXAS INSTRUMENTS INC
元件分类: 稳压器
英文描述: SWITCHING REGULATOR, PDSO6
封装: 2 X 2 MM, GREEN, PLASTIC, SON-6
文件页数: 10/33页
文件大小: 5549K
代理商: TPS62122DRVT
SWmax
1
f
= 770 kHz
1.3 s
(
)
min
max
D SON max
L
Vin
= Vout
+ Iout
R
+ R
SLVSAD5 – JULY 2010
www.ti.com
The maximum switch frequency can be estimated to:
(3)
100% DUTY CYCLE LOW DROPOUT OPERATION
The device will increase the On Time of the high-side MOSFET switch once the input voltage comes close to the
output voltage in order to keep the output voltage in regulation. This will reduce the switch frequency.
With further decreasing input voltage VIN the high-side MOSFET switch is turned on completely. In this case the
converter provides a low input-to-output voltage difference. This is particularly useful in applications with widely
variable supply voltage to achieve longest operation time by taking full advantage of the whole supply voltage
span.
The minimum input voltage to maintain regulation depends on the load current and output voltage, and can be
calculated as:
(4)
With:
IOUTmax = maximum output current
RDS(ON)max = maximum P-channel switch RDS(ON).
RL = DC resistance of the inductor
VOUTmax = nominal output voltage plus maximum output voltage tolerance
UNDER-VOLTAGE LOCKOUT
The under-voltage lockout circuit prevents the device from misoperation at low input voltages. It prevents the
converter from turning on the high-side MOSFET switch or low-side MOSFET under undefined conditions. The
UVLO threshold is set to 2.5V typical for rising VIN and 1.85V typical for falling VIN. The hysteresis between
rising and falling UVLO threshold ensures proper start up even with high impedance sources. Fully functional
operation is permitted for an input voltage down to the falling UVLO threshold level. The converter starts
operation again once the input voltage trips the rising UVLO threshold level.
SOFT START
The TPS6212X has an internal soft-start circuit which controls the ramp up of the output voltage and limits the
inrush current during start-up. This limits input voltage drop when a battery or a high-impedance power source is
connected to the input of the converter.
The soft-start system generates a monotonic ramp up of the output voltage with a ramp of typically 15mV/s and
reaches an output voltage of 1.8V in typically 170s after EN pin was pulled high. TPS6212X is able to start into
a pre biased output capacitor. The converter starts with the applied bias voltage and ramps the output voltage to
its nominal value.
During start up the device can provide an output current of half of the high-side MOSFET switch current limit
ILIMF. Large output capacitors and high load currents may exceed the current capability of the device during start
up. In this case the start up ramp of the output voltage will be slower.
ENABLE/SHUTDOWN
The device starts operation when EN pin is set high and the input voltage VIN has tripped the under voltage
lockout threshold UVLO for rising VIN. It starts switching after the regulator start up time tStart of typically 50s has
expired and enters the soft start as previously described. For proper operation, the EN pin must be terminated
and must not be left floating.
EN pin low forces the device into shutdown, with a shutdown quiescent current of typically 0.3A.
In this mode, the high-side and low-side MOSFET switches as well as the entire internal-control circuitry are
switched off.
In TPS62120 the internal N-MOSFET at pin SGND is activated and connects SGND to GND.
18
Copyright 2010, Texas Instruments Incorporated
Product Folder Link(s): TPS62120 TPS62122
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