TPS62134A, TPS62134B, TPS62134C, TPS62134D
ZHCSD94C –JANUARY 2015–REVISED JANUARY 2015
www.ti.com.cn
9.3 Feature Description
9.3.1 Enable and Shutdown (EN)
When the EN pin is set high, the device begins operation. The EN pin allows sequencing from a host or power-
good output of another device.
The devices enter shutdown mode if the EN pin is pulled low with a shutdown current of 2 µA (typical). During
shutdown, the internal power MOSFETs as well as the entire control circuitry are turned off. The output capacitor
is smoothly discharged by a 20-kΩ internal resistor through the VOS pin. An internal pulldown resistor of
approximately 400 kΩ is connected and maintains EN logic low, if the pin is floating. The pulldown resistor is
disconnected if the EN pin is high.
9.3.2 Undervoltage Lockout (UVLO)
If the input voltage drops, the undervoltage lockout prevents misoperation of the device by switching off both
power MOSFETs. The UVLO threshold is set to 2.7 V (typical). The device is fully operational for voltages above
the UVLO threshold and turns off if the input voltage trips the threshold. The converter begins operation again
when the input voltage exceeds the threshold by a hysteresis of 200 mV (typical).
9.3.3 Soft-Start (SS) Circuitry
The internal soft-start circuitry controls the output-voltage slope during startup. This control avoids excessive
inrush current and ensures a controlled output-voltage rise time. The control also prevents unwanted voltage
drops from high-impedance power sources or batteries. When the EN pin is set high to begin device operation,
the device begins switching after a delay of approximately 50 µs and VO rises up to the nominal value set by the
VIDx pins with a slope controlled by an external capacitor connected to the SS pin. Leave the SS pin floating for
the fastest startup.
The device can startup into a pre-biased output. During monotonic pre-biased startup, both power MOSFETs are
not allowed to turn on until the internal ramp of the device sets an output voltage above the pre-bias voltage.
If the device is in shutdown mode, undervoltage lockout, or thermal shutdown, an internal resistor pulls the SS
pin down to ensure a proper low level. Returning from those states causes a new startup sequence.
9.3.4 Switch Current-Limit and Short Circuit Protection
The TPS62134x family of devices is protected against heavy load and short circuit events. If an output short
circuit is detected (VO drops below 0.3 V), the switch current limit is reduced to 1.6 A (typical). If the output
voltage rises above 0.4 V, the device operates in normal operation again.
At heavy loads, the current-limit determines the maximum output current. The current-limit supports output
currents of 3 A with input voltages below 5 V and 3.2 A with higher input voltages. If the peak current-limit (IL) is
reached, the high-side MOSFET is turned off. Avoiding shoot-through current, the low-side MOSFET is switched
on to sink the inductor current. The high-side MOSFET turns on again, only if the current in the low-side
MOSFET has decreased below the low-side current-limit threshold of 3.2 A (typical).
Because of the internal propagation delay, the actual peak current of the high-side switch typically occurs above
the DC value listed in the Electrical Characteristic table, especially in low duty-cycle applications. Use 公式 1 to
calculate the dynamic current-limit.
V - VO
I
IL(dynamic) = IL +
´ 30 ns
L
(1)
9.3.5 Output Voltage and LPM Logic Selection (VIDx and LPM)
The output voltage of the TPS62134x family of devices is selected by two VIDx pins and one LPM pin as listed in
表 1. A pulldown resistor of 400 kΩ is internally connected to the VIDx pins and LPM pin to ensure a proper logic
level if the pin is high impedance or floating. The pulldown resistors are disconnected if the pins are pulled High.
The device has a low power mode (LPM) where the output voltage is reduced or disabled by using the LPM pin.
While the LPM pin is asserted, the PG output remains high impedance. The device also achieves a dynamic
output-voltage change by using the VIDx pins. This feature helps the system to minimize power consumption in
standby or idle mode. The TPS62134B/D devices provide the full current even if the output voltage is set at 0.7 V
in LPM mode.
8
版权 © 2015, Texas Instruments Incorporated
QQ：528164397 复制
