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| TPS61253_16 Datasheet, PDF (15/35 Pages) Texas Instruments – High Efficiency Step-Up Converter In Chip Scale Packaging | |||
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TPS61253, TPS61254, TPS61256, TPS61258, TPS61259, TPS612592
SLVSAG8F â SEPTEMBER 2011 â REVISED MARCH 2016
9.3 Feature Description
9.3.1 Current Limit Operation
The TPS6125x device employs a valley current limit sensing scheme. Current limit detection occurs during the
off-time by sensing of the voltage drop across the synchronous rectifier.
The output voltage is reduced as the power stage of the device operates in a constant current mode. The
maximum continuous output current (IOUT(CL)), before entering current limit (CL) operation, can be defined by
Equation 1.
1
I
OUT(CL)
=
(1 -
D)
g
(I +
VALLEY
2
DIL )
(1)
The duty cycle (D) can be estimated by Equation 2
D = 1-
V
IN
g
h
V
OUT
(2)
and the peak-to-peak current ripple (ÎIL) is calculated by Equation 3
DIL
=
VIN
L
g
D
f
(3)
The output current, IOUT(DC), is the average of the rectifier ripple current waveform. When the load current is
increased such that the lower peak 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 26 illustrates the inductor and rectifier current waveforms during current limit operation.
Rectifier
Current
IOUT(DC)
IL
Current Limit
Threshold
DIL
IPEAK
IVALLEY = ILIM
IOUT(CL)
Increased
Load Current
IIN(DC)
Inductorr
Current
f
DIL
ÎI L =
VIN
Ã
D
Lf
IIN(DC)
Figure 26. Inductor/Rectifier Currents in Current Limit Operation
9.3.2 Enable
The TPS6125x device starts operation when EN is set high and starts up with the soft-start sequence. For proper
operation, the EN pin must be terminated and must not be left floating.
Pulling the EN and BP pins low forces the device in shutdown, with a shutdown current of typically 1 µA. In this
mode, true load disconnect between the battery and load prevents current flow from VIN to VOUT, as well as
reverse flow from VOUT to VIN.
Pulling the EN pin low and the BP pin high forces the device in standby mode, refer to the Standby Mode section
for more details.
Copyright © 2011â2016, Texas Instruments Incorporated
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Product Folder Links: TPS61253 TPS61254 TPS61256 TPS61258 TPS61259 TPS612592
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