I
LIM
2
I
LIM
4
10
TPS61040, TPS61041
SLVS413I – OCTOBER 2002 – REVISED DECEMBER 2016
www.ti.com
Product Folder Links:
TPS61040 TPS61041
Submit Documentation Feedback
Copyright © 2002–2016, Texas Instruments Incorporated
Feature Description (continued)
7.3.2 Soft Start
All inductive step-up converters exhibit high inrush current during start-up if no special precaution is made. This
can cause voltage drops at the input rail during start up and may result in an unwanted or early system shut
down.
The TPS6104x limits this inrush current by increasing the current limit in two steps starting from
for 256
cycles to
for the next 256 cycles, and then full current limit (see
Figure 15
).
7.3.3 Enable
Pulling the enable (EN) to ground shuts down the device reducing the shutdown current to 1
μ
A (typical).
Because there is a conductive path from the input to the output through the inductor and Schottky diode, the
output voltage is equal to the input voltage during shutdown. The enable pin needs to be terminated and should
not be left floating. Using a small external transistor disconnects the input from the output during shutdown as
shown in
Figure 17
.
7.3.4 Undervoltage Lockout
An undervoltage lockout prevents misoperation of the device at input voltages below typical 1.5 V. When the
input voltage is below the undervoltage threshold, the main switch is turned off.
7.3.5 Thermal Shutdown
An internal thermal shutdown is implemented and turns off the internal MOSFETs when the typical junction
temperature of 168°C is exceeded. The thermal shutdown has a hysteresis of typically 25°C. This data is based
on statistical means and is not tested during the regular mass production of the IC.
7.4 Device Functional Modes
7.4.1 Operation
The TPS6104x operates with an input voltage range of 1.8 V to 6 V and can generate output voltages up to 28
V. The device operates in a pulse-frequency-modulation (PFM) scheme with constant peak current control. This
control scheme maintains high efficiency over the entire load current range, and with a switching frequency up to
1 MHz, the device enables the use of very small external components.
The converter monitors the output voltage, and as soon as the feedback voltage falls below the reference voltage
of typically 1.233 V, the internal switch turns on and the current ramps up. The switch turns off as soon as the
inductor current reaches the internally set peak current of typically 400 mA (TPS61040) or 250 mA (TPS61041).
See
Peak Current Control
for more information. The second criteria that turns off the switch is the maximum on-
time of 6
μ
s (typical). This is just to limit the maximum on-time of the converter to cover for extreme conditions.
As the switch is turned off the external Schottky diode is forward biased delivering the current to the output. The
switch remains off for a minimum of 400 ns (typical), or until the feedback voltage drops below the reference
voltage again. Using this PFM peak current control scheme the converter operates in discontinuous conduction
mode (DCM) where the switching frequency depends on the output current, which results in very high efficiency
over the entire load current range. This regulation scheme is inherently stable, allowing a wider selection range
for the inductor and output capacitor.
