參數(shù)資料
型號: TPS56221DQPR
廠商: TEXAS INSTRUMENTS INC
元件分類: 穩(wěn)壓器
英文描述: SWITCHING CONTROLLER, PDSO22
封裝: ROHS COMPLIANT, PLASTIC, SON-22
文件頁數(shù): 4/25頁
文件大?。?/td> 655K
代理商: TPS56221DQPR
SLUSAH5
– MARCH 2011
An overcurrent (OC) condition is detected by sensing voltage drop across the low-side FET and across the
high-side FET. If the voltage drop across either FET exceeds OC threshold, a count increments one count. If no
OC condition is detected on either FET, the fault counter decrements by one counter. If three OC pulses are
summed, a fault condition is declared which cycles the soft-start function in a hiccup mode. Hiccup mode is
defined as four dummy soft-start timeouts followed by a real one if overcurrent condition is encountered during
normal operation; or five dummy soft-start timeouts followed by a real one if overcurrent condition occurs from
the beginning during start. This cycle continues indefinitely until the fault condition is removed.
Input Undervoltage Lockout (UVLO)
The TPS56221 has fixed input under-voltage lockout (UVLO). In order for the device to turn on, the following
conditions must be met:
the EN/SS pin voltage must be greater than VIH
the input voltage must exceed UVLO on voltage VUVLO
The UVLO has a minimum of 500 mV hysteresis built-in.
Pre-Bias Startup
The TPS56221 contains a unique circuit to prevent current from being pulled from the output during startup in the
condition the output is pre-biased. There are no PWM pulses until the internal soft-start voltage rises above the
error amplifier input (FB pin), if the output is pre-biased. Once the soft-start voltage exceeds the error amplifier
input, the controller slowly initiates synchronous rectification by starting the synchronous rectifier with a narrow
on time. It then increments the on-time on a cycle-by-cycle basis until it coincides with the time dictated by (1-D),
where D is the duty cycle of the converter.
This approach prevents the sinking of current from a pre-biased output, and ensures the output voltage startup
and ramp to regulation is smooth and controlled.
Power Good
The TPS56221 provides an indication that output is good for the converter. This is an open drain signal and pulls
low when any condition exists that would indicate that the output of the supply might be out of regulation. These
conditions include:
VFB is more than ±12.5% from nominal
soft-start is active
a short circuit condition has been detected
NOTE
When there is no power to the device, PGOOD is not able to pull close to GND if an
auxiliary supply is used for the power good indication. In this case, a built in resistor
connected from drain to gate on the PGOOD pull down device makes the PGOOD pin
look approximately like a diode to GND.
Thermal Shutdown
If the junction temperature of the device reaches the thermal shutdown limit of 145
°C, the PWM and the oscillator
are turned off. Both high-side FET and low-side FET are kept off. When the junction cools to the required level
(125
°C typical), the PWM initiates soft start as during a normal power-up cycle.
12
Copyright
2011, Texas Instruments Incorporated
Product Folder Link(s) :TPS56221
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