TPS61280 Datasheet, PDF (28/58 Pages) Texas Instruments – Low-, Wide- Voltage Battery Front-End DC/DC Converter Single-Cell Li-Ion, Ni-Rich, Si-Anode Applications

TPS61280, TPS61281, TPS61282
SLVSBI1 – OCTOBER 2013
www.ti.com
f_m < RBW: The receiver is not able to distinguish individual side-band harmonics, so, several harmonics are
added in the input filter and the measured value is higher than expected in theoretical calculations.
f_m > RBW: The receiver is able to properly measure each individual side-band harmonic separately, so the
measurements match with the theoretical calculations.
CURRENT LIMIT OPERATION
The TPS6128x device features a valley inductor current limit scheme.
In dc/dc boost mode, the TPS6128x device employs a current limit detection scheme in which the voltage drop
across the synchronous rectifier is sensed during the off-time. In the TPS61280 the current limit threshold can be
set via an I²C register. TPS6128x devices have a fixed current limit threshold. See device ordering table for
detailed information.
The output voltage is reduced as the power stage of the device operates in a constant current mode. The
maximum continuous output current (I_OUT(MAX)), before entering current limit (CL) operation, can be defined by
Equation 6.
I_OUT(MAX) = I_LIM g
V_IN
V_OUT
gh
(6)
The inductor peak-to-peak current ripple (ΔI_L) is calculated by Equation 7
DI_L
=
V_IN
L
g
D
f
(7)
The output current, I_OUT(DC), is the average of the rectifier ripple current waveform. When the load current is
increased such that the trough is above the current limit threshold, the off-time is increased to allow the current to
decrease to this threshold before the next on-time begins (so called frequency fold-back mechanism). When the
current limit is reached the output voltage decreases during further load increase.
Figure 44 illustrates the inductor and rectifier current waveforms during current limit operation.
Rectifier
Current
I_OUT(DC)
IL
Current Limit
Threshold
DI_L
I_PEAK
I_VALLEY
I_OUT
Increased
Load Current
I_IN(DC)
Inductor
Current
f
DI_L
ΔI _L = ^VIN× ^D
Lf
I_IN(DC)
Figure 44. Inductor/Rectifier Currents in Current Limit Operation (DC/DC Boost Mode)
During pass-through mode, the TPS6128x device is short-circuit protected by a very fast current limit detection
scheme. If the current in the bypass FET exceeds approximately 7.5Amps a fault is declared and the device
cycles through a start-up procedure.
28
Submit Documentation Feedback
Copyright © 2013, Texas Instruments Incorporated
Product Folder Links: TPS61280 TPS61281 TPS61282