Datasheet
HS LS
Vout 0.8V
R = R
0.8 V
-
æ ö
´
ç ÷
è ø
4.7
0 0.1 0.15 0.35 0.5
Load Current - A
V - Input Voltage - V
I
Start Stop
4.8
4.9
5
5.1
5.3
4.6
5.4
5.5
5.6
5.2
0.05 0.250.2 0.3 0.4 0.45
Dropout
Voltage
Dropout
Voltage
TPS54560
www.ti.com
SLVSBN0A –MARCH 2013–REVISED MARCH 2014
Feature Description (continued)
• VBOOT = (1.41 x V
IN
- 0.554 - VF / TSW - 1.847 x 10
3
x IB2SW) / (1.41 + 1 / Tsw)
• R
DS(on)
= 1 / (-0.3 x VB2SW
2
+ 3.577 x VB2SW - 4.246) (1)
Figure 23. 5V Start/Stop Voltage
8.3.5 Error Amplifier
The TPS54560 voltage regulation loop is controlled by a transconductance error amplifier. The error amplifier
compares the FB terminal voltage to the lower of the internal soft-start voltage or the internal 0.8 V voltage
reference. The transconductance (gm) of the error amplifier is 350 μA/V during normal operation. During soft-
start operation, the transconductance is reduced to 78 μA/V and the error amplifier is referenced to the internal
soft-start voltage.
The frequency compensation components (capacitor, series resistor and capacitor) are connected between the
error amplifier output COMP terminal and GND terminal.
8.3.6 Adjusting the Output Voltage
The internal voltage reference produces a precise 0.8 V ±1% voltage reference over the operating temperature
and voltage range by scaling the output of a bandgap reference circuit. The output voltage is set by a resistor
divider from the output node to the FB terminal. It is recommended to use 1% tolerance or better divider
resistors. Select the low side resistor R
LS
for the desired divider current and use Equation 2 to calculate R
HS
. To
improve efficiency at light loads consider using larger value resistors. However, if the values are too high, the
regulator will be more susceptible to noise and voltage errors from the FB input current may become noticeable.
(2)
8.3.7 Enable and Adjusting Undervoltage Lockout
The TPS54560 is enabled when the VIN terminal voltage rises above 4.3 V and the EN terminal voltage exceeds
the enable threshold of 1.2 V. The TPS54560 is disabled when the VIN terminal voltage falls below 4 V or when
the EN terminal voltage is below 1.2 V. The EN terminal has an internal pull-up current source, I1, of 1.2 μA that
enables operation of the TPS54560 when the EN terminal floats.
If an application requires a higher undervoltage lockout (UVLO) threshold, use the circuit shown in Figure 24 to
adjust the input voltage UVLO with two external resistors. When the EN terminal voltage exceeds 1.2 V, an
additional 3.4 μA of hysteresis current, I
HYS
, is sourced out of the EN terminal. When the EN terminal is pulled
below 1.2 V, the 3.4 μA Ihys current is removed. This additional current facilitates adjustable input voltage UVLO
hysteresis. Use Equation 3 to calculate R
UVLO1
for the desired UVLO hysteresis voltage. Use Equation 4 to
calculate R
UVLO2
for the desired VIN start voltage.
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