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参数资料
| 型号： | TPS61170DRVTG4 |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | 1.44 A SWITCHING REGULATOR, 1500 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封装： | 2 X 2 MM, GREEN, PLASTIC, SON-6 |
| 文件页数： | 29/29页 |
| 文件大小： | 689K |
| 代理商： | TPS61170DRVTG4 |
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SLVS789C
– NOVEMBER 2007 – REVISED APRIL 2011
DETAILED DESCRIPTION
OPERATION
The TPS61170 integrates a 40-V low side FET for providing output voltages up to 38 V. The device regulates the
output with current mode PWM (pulse width modulation) control. The switching frequency of the PWM is fixed at
1.2MHz (typical). The PWM control circuitry turns on the switch at the beginning of each switching cycle. The
input voltage is applied across the inductor and stores the energy as the inductor current ramps up. During this
portion of the switching cycle, the load current is provided by the output capacitor. When the inductor current
rises to the threshold set by the error amplifier output, the power switch turns off and the external Schottky diode
is forward biased. The inductor transfers stored energy to replenish the output capacitor and supply the load
current. This operation repeats each switching cycle. As shown in the block diagram, the duty cycle of the
converter is determined by the PWM control comparator which compares the error amplifier output and the
current signal.
A ramp signal from the oscillator is added to the current ramp. This slope compensation ramp is necessary to
avoid sub-harmonic oscillations that are intrinsic to current mode control at duty cycles higher than 50%. The
feedback loop regulates the FB pin to a reference voltage through an error amplifier. The output of the error
amplifier must be connected to the COMP pin. An external RC compensation network must be connected to the
COMP pin to optimize the feedback loop for stability and transient response.
SOFT START-UP
Soft-start circuitry is integrated into the IC to avoid a high inrush current during start-up. After the device is
enabled by a logic high signal on the CTRL pin, the FB pin reference voltage ramps up in 32 steps, with each
step taking 213
μs. This ensures that the output voltage rises slowly to reduce inrush current. Additionally, for the
first 5 msec after the COMP voltage ramps, the current limit of the PWM switch is set to half of the normal
current limit specification or below 700mA (typical). See the start-up waveform for a typical example, Figure 11.
OVERCURRENT PROTECTION
TPS61170 has a cycle-by-cycle overcurrent limit feature that turns off the power switch once the inductor current
reaches the overcurrent limit. The PWM circuitry resets itself at the beginning of the next switch cycle. During an
over-current event, this results in a decrease of output voltage that is directly proportional to load current. The
current limit threshold as well as input voltage, output voltage, switching frequency and inductor value determine
the maximum available output current. Larger inductance values typically increase the current output capability
because of the reduced current ripple. See the APPLICATION INFORMATION section for the output current
calculation.
UNDERVOLTAGE LOCKOUT (UVLO)
An undervoltage lockout prevents mis-operation of the device at input voltages below 2.2V (typical). When the
input voltage is below the undervoltage threshold, the device remains off and the internal switch FET is turned
off. The undervoltage lockout threshold is set below minimum operating voltage of 3V to avoid any transient VIN
dip triggering the UVLO and causing the device to reset. For the input voltages between UVLO threshold and 3V,
the device attempts operation, but the specifications are not ensured.
THERMAL SHUTDOWN
An internal thermal shutdown turns off the device when the typical junction temperature of 160
°C is exceeded.
The IC restarts when the junction temperature drops by 15
°C.
ENABLE AND SHUTDOWN
The TPS61170 enters shutdown when the CTRL voltage is less than 0.4V for more than 2.5ms. In shutdown, the
input supply current for the device is less than 1
μA (max). The CTRL pin has an internal 800k (typical) pull
down resistor to disable the device when the pin is left unconnected.
Copyright
2007–2011, Texas Instruments Incorporated
9
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