ST ST7LIT15BY0 User manual

February 2008 Rev 1 1/21
UM0497
User manual
USB Li-Ion battery charger evaluation board
Introduction
This document explains the functioning of the USB-based single cell Li-Ion battery charger
evaluation board which consists of a ST7260E2-based low-speed USB controller and a
battery charger based on the ST7LIT15BY0.
The evaluation board includes a power selector circuit to select the appropriate power
supply source and a step-up converter circuit based on the L6920 device to provide a fixed
output voltage to the USB controller. The power supply for the battery charger controller is
generated from the TL1431programmable voltage reference, keeping in mind the accuracy
requirement for charging. An additional current limiter is also included in series with a USB
power supply to show any incorrect behavior using a status LED.
A provision is provided on evaluation board such that any external low-speed USB controller
can control the operation of the charger, hence this system can be used with any low-speed
USB controller.
The charger used in the board utilizes a modified form of non-inverting buck-boost converter
to support the charging voltage requirement for single cell Li-Ion battery. This converter is
explained in more detail in AN2390.
This evaluation board represents a complete USB-based portable battery charging system
for a single cell Li-Ion battery, such as those used in MP3 players.
There are separate ICP connectors provided on the board to reprogram the USB controller
and charger controller.
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Contents UM0497
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Contents
1 Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Package contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Hardware description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1 Power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.2 Current limiter (ST890B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.3 Precision supply for the charger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.4 Preferential power selector circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.5 Supply generation circuit for the USB controller . . . . . . . . . . . . . . . . . . . 6
1.2.6 Supply shutdown control circuit for the USB controller . . . . . . . . . . . . . . 6
1.2.7 Jumpers and connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.8 DC-DC converter circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2 Running the evaluation board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1 Connecting to the PC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Connecting the Li-Ion battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3 Battery charging status monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4 Controlling/changing the charging parameters . . . . . . . . . . . . . . . . . . . . . 11
3 Using the external USB controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4 Using the charger in standalone mode . . . . . . . . . . . . . . . . . . . . . . . . . 14
5 Warning/limitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6 Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Appendix A Schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1 USB battery charger BOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

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List of figures
Figure 1. USB Li-Ion evaluation board (STEVAL-ISB003V1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Figure 2. Reference voltage generation for the charger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 3. Power selector circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 4. Supply generation circuit for the USB controller. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 5. Connector J2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 6. Clock selector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 7. DC-DC converter circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 8. Enumeration result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 9. USB Li-Ion evaluation board HID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 10. Li-Ion battery 3-pin connector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 11. Schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Getting started UM0497
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1 Getting started
1.1 Package contents
The USB Li-Ion battery charger evaluation board includes the following items:
●Hardware content:
– One evaluation board
●Documentation:
–Usermanual
1.2 Hardware description
Figure 1 below shows the snapshot of the evaluation board.
Figure 1. USB Li-Ion evaluation board (STEVAL-ISB003V1)
1.2.1 Power supply
The evaluation board is powered by a USB bus directly. As only 100 mA current is available
by default from the USB bus, the charger is inititally kept in shutdown mode. After proper
enumeration is done by the USB controller to increase the supply current limit to 500 mA,
the charger switches to ON to start charging the battery.
1.2.2 Current limiter (ST890B)
To provide additional information about the USB supply current, a current limiter (ST890B) is
kept in series of the USB supply. There is a STATUS LED (D3) connected with the FAULT
pin of this current limiter.

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This LED glows HIGH whenever the supply current increases from 500 mA. In the
evaluation board, the current limiter is used only to show the status of whether the current
limit is crossed or not, but it is not used to cut off the power supply.
1.2.3 Precision supply for the charger
Figure 2 shows circuit for the precision supply for the charger system. Here TL1431AI,
which provides 0.25% accurate reference voltage, is used to generate a precise voltage
supply for the charger system.
Figure 2. Reference voltage generation for the charger
With the help of this precision supply, we can easily achieve the 1% accuracy target which is
mandatory for Li-Ion charger systems.
1.2.4 Preferential power selector circuit
Figure 3 shows a preferential power selector circuit which is used to select the source power
supply for the USB controller.
Figure 3. Power selector circuit
This selector circuit works as follows. Whenever the USB supply (VBUS) is available, it is
used as the source supply. Battery power is only used when the USB supply is not available.

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1.2.5 Supply generation circuit for the USB controller
Figure 4 shows L6920-based supply generation circuit for the USB controller. USB_SUPPLY
is the output voltage and VREG (output voltage of the power selector circuit as in
Section 1.2.4) is the input voltage of this circuit. The output voltage USB_SUPPLY is
programmable. In the evaluation board it is set at 4.5 voltage and depends on the ratio
R4/R9. Please refer to the L6920 datasheet for more details.
Figure 4. Supply generation circuit for the USB controller
LED (D4) is used to show the status of the input supply availability which glows whenever
the input supply falls below a certain threshold (determined by the voltage at LBI).
1.2.6 Supply shutdown control circuit for the USB controller
The STM1061 as shown in Figure 4 is used to control the shutdown operation of the L6920.
It puts the L6920 in shutdown mode whenever the input supply voltage falls below 2.5 V.
1.2.7 Jumpers and connectors
The following important jumpers control the operation of the evaluation board and are
explained according to their applications:
J2, JP1, JP3, JP12, JP13, JP14 and JP16 are used to select between the USB controller
available on the evaluation board and the external USB controller.

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The role of each individual jumpers is as follows:
●JP1: to connect USB_SUPPLY to the VDD pin of the USB controller
●JP3: to connect USBVCC to USBDM through a 1.5 kΩresistor.
●JP12: to monitor the availability of the VBUS signal.
●JP15: to connect to the SHDN_CHG pin of the charger. This is used to put the charger
in shutdown mode until proper enumeration is done.
●JP13, JP14: These are used to connect to the status pin
●JP16: to connect the USB supply pin to the demonstration board supply pin. Pin 1 of
this jumper is the USB supply pin (USB_VDD) and pin 2 is the demonstration supply pin
(VBUS). For the standalone charger, please connect the external supply to pin 2 of
JP16.
●J2: As shown in Figure 5, this is a 7-pin connector and can be used to connect to the
external USB controller.
Figure 5. Connector J2
Warning: You can connect to only one USB controller at a time. If you
want to use an external USB controller, you must open all the
jumpers (JP1, JP3, JP12, JP13, JP14 and JP15) required by
the USB controller.
J5 and J7: These are 3-pin connectors and are used to select between the ICC clock and
resonator clock. J5 is used for selecting the clock source for the USB controller (ST7260E2)
available in the evaluation board and J7 is used to select the clock source of the charger IC
(ST7LIT15BY0). As shown in Figure 6, if we short pin 1 and 2 then the external resonator is
used as the clock source and if we short pin 2 and pin 3, ICC clock is used as the clock
source. In general we short pin 1 and pin 2.
Figure 6. Clock selector

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1.2.8 DC-DC converter circuit
Figure 7 shows the circuit diagram of the DC-DC converter circuit which is controlled by the
two PWM signals coming from the charger controller ST7LIT15BY0.
Figure 7. DC-DC converter circuit
This DC-DC converter provides power to the single cell Li-Ion (3-pin battery pack) based on
the battery voltage, current and temperature measurements. Please refer to AN2390 for
more details regarding this DC-DC converter circuit.

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2 Running the evaluation board
After ensuring that all the jumpers are connected correctly as explained in the previous
section, the evaluation board is ready to be used.
2.1 Connecting to the PC
As soon as you connect the USB connector to the evaluation board, you should find the
evaluation board enumerated as an HID device as shown Figure 8.
Figure 8. Enumeration result
And if you check the properties of all these HID devices, you should find the property of one
HID device as shown in Figure 9.

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Figure 9. USB Li-Ion evaluation board HID
This ensures that the evaluation board is connected properly to the USB and now ready to
be used. Now we can proceed to the next steps.
2.2 Connecting the Li-Ion battery
The evaluation board is not provided with any specific slot in order to avoid making it
package specific. Instead a 3-pin connector is provided on the evaluation board as shown in
Figure 10.
Figure 10. Li-Ion battery 3-pin connector
You can either solder a particular slot to this connector and then connect the battery in that
slot, or if you are directly connecting the battery to the connector, please ensure that the
battery is properly connected as improper connection may affect the accuracy of the analog
measurement,thus affecting the overall accuracy of the charging.