TPS62480 Datasheet, PDF (10/36 Pages) Texas Instruments – 2-Phase Step-Down Converter

TPS62480
SLVSCL9A – FEBRUARY 2016 – REVISED FEBRUARY 2016
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Feature Description (continued)
7.3.8 Active Output Discharge
The VO pin, connected to the output voltage, provides an active discharge path when the device is switched off
by setting EN Low or UVLO event. In case of being activated, this discharge circuit sinks typically 120mA for
output voltages of typically 1 V and above. If V_OUT is lower, the active current sink enters linear operation mode
and the discharge current decreases.
7.3.9 Undervoltage Lockout (UVLO)
The undervoltage lockout prevents misoperation of the device, if the input voltage drops below the UVLO
threshold which is set to typically 2.3 V. The converter starts operation again once the input voltage exceeds the
threshold by a hysteresis of typically 200 mV.
7.3.10 Thermal Shutdown
The junction temperature (T_J) of the device is monitored by an internal temperature sensor. If T_J exceeds 160°C
(typical), the device goes in thermal shutdown with a hysteresis of about 10°C. Both the power FETs are turned
off and the PG pin goes Low. Once T_J has decreased enough, the device resumes normal operation with Soft
Start.
7.4 Device Functional Modes
7.4.1 Pulse Width Modulation (PWM) Operation
The TPS62480 is based on a predictive OFF-time peak current control topology, operating with PWM in
continuous conduction mode for heavier loads. The switching frequency is typically 2.2MHz. Both the master and
follower phase regulate to the same VOUT level, each with a separate current loop, using the same peak current
set point, cycle by cycle. This provides excellent peak current balancing, independent of inductor dc resistance
matching. Since the follower phase operates with an adaptive delay to the master phase, phase shifted operation
is always obtained. If the load current decreases, the device runs with the master phase only (see Phase
Add/Shed and Current Balancing).
PWM only mode can be forced by pulling MODE pin High. If MODE is set Low, the device features an automatic
transition into Power Save Mode, entered at light loads, running in discontinuous conduction mode (DCM).
7.4.2 Power Save Mode (PSM) Operation
As the load current decreases to half the ripple current, the converter enters Power Save Mode operation. During
PSM, the converter operates with reduced switching frequency maintaining high conversion efficiency. Power
Save Mode is based on an adaptive peak current target, to keep output voltage ripple low. Since each pulse
shifts V_OUT up, a pause time happens until V_OUT trips the internal V_{OUT_Low} threshold again and the next pulse
takes place.
The switching frequency in PSM (one phase operation) calculates as:
space
( ) _fSW(PSM)
=
2 × I_OUT × V_OUT V_IN -
L × I_P2EAK × V_IN
V_OUT
(1)
10
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