Datasheet

1
2
3
4
TPS2511
8
7
6
5
GND
ILIM_SET
IN
CS
PAD
OUT
DM
DP
EN
UDG-12096
R
ILIM
0.1 mF
100 kW
C
USB
GND
D+
D−
V
BUS
USB Connector
R
1
R
2
R
3
C
OUT
5.0 V
FB
GND
AC-to-DC Converter
or
Buck DC -to-DC
Converter
R
4
5V
OUT
Power Supply
I
OUT
Portable Device
Cable
I
OUT
VPD_IN
ILIM
22.227 k
R 22.007 k
1.01 k
W
= = W
W
1
1
1.03
1.03
ILIM
OS _ MIN
51228 51228
R 22.227 k
I 2100
æ ö
æ ö
ç ÷
= = = W
ç ÷
ç ÷
è ø
è ø
OS _ MIN
1.03
ILIM
51228
I 2100 mA
R
= =
TPS2511
SLUSB18 –JUNE 2012 www.ti.com
Current Limit Setpoint Example
In the following example, choose the ILIM_SET resistor to ensure that TPS2511 does not trip off under worst
case conditions of current limit and resistor tolerance (assume 1% resistor tolerance). For this example, I
OS_MIN
=
2100 mA.
(4)
(5)
Including resistor tolerance, target nominal resistance value:
(6)
Choose:
R
ILIM
= 22.0 kΩ (7)
V
BUS
Voltage Drop Compensation
Figure 33 shows a USB charging design using the TPS2511. In general V
BUS
has some voltage loss due to USB
cable resistance and TPS2511 power switch on-state resistance. The sum of voltage loss is likely several
hundred millivolts from 5V
OUT
to V
PD_IN
that is the input voltage of PD while the high charging current charges the
PD. For example, in Figure 34, assuming that the loss resistance is 170 mΩ (includes 100 mΩ of USB cable
resistance and 70 mΩ of power switch resistance) and 5V
OUT
is 5.0 V, the input voltage of PD (V
PD_IN
) is about
4.66 V at 2.0 A. (see Figure 34)
The charging current of most portable devices is less than their maximum charging current while V
PD_IN
is less
than the certain voltage value. Furthermore actual charging current of PD decreases with input voltage falling.
Therefore, a portable devices cannot accomplish a fast charge with its maximum charging rated current if V
BUS
voltage drop across the power path is not compensated at the high charging current. The TPS2511 provides CS
pin to report the high charging current for USB chargers to increase the 5V
OUT
voltage. This is shown by the solid
lines of Figure 34.
Figure 33. TPS2511 Charging System Schematic Diagram
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Product Folder Link(s) :TPS2511