10
Rev. 0
EVALUATE USB BC 1.2 CDP APPLICATIONS
The LT8698S/LT8698S-1 integrates necessary hardware
to support USB BC 1.2 Charging Downstream Port (CDP)
charger profile which allows compliant devices to draw
high current of up to 1.5A from V
BUS
while simultane-
ously communicating with the host at USB high speed
of 480Mbps.
Refer to Figure 10 for proper measurement equipment
setup and follow the procedure below.
1. Check that JP6 is placed on the ON position to ensure
that the 3.3V LDO is enabled.
2. Select JP2 and JP3 to be in the LOW position and
select JP4 to be in the LOW or TRI position. Select
JP4 SEL3 in the LOW position sets the LT8698S/
LT8698S-1 in select state 0 which performs the
CDP sequence with the data line switches closed
and without termination. Select JP4 SEL3 in the TRI
position sets the LT8698S/LT8698S-1 in select state
1 which performs the CDP sequence with the data line
switches open and 20k termination resistors tied from
HD+ and HD– to GND. Both select 0 and select 1 are
valid state in which to start the CDP sequence. For
further information about the CDP sequence, please
refer to the LT8698S/LT8698S-1 data sheet.
3. With power off, connect the input power supply to
V
EMI
and GND turrets. If the EMI/EMC performance
is not important, connect the input power supply to
V
IN
and GND turrets.
4. Check that JP1 EN jumper is placed on the ON position.
5. Turn on the power at the input.
NOTE:
Make sure that the input voltage never
exceeds 42V.
6. Check for proper output voltages: V
BUS
= 5V, and D11
LED indicator lights up in green.
7. Plug a USB cable connecting to a PC with type B
connector to the type B socket of the DC2688A demo
board and connect the USB cable to a computer.
8. Check the STATUS pin voltage and observe STATUS
yellow LED is on, meaning STATUS pin is low. At this
point, the LT8698S/LT8698S-1 puts a 100μA current
source on the D+, asserts STATUS low and waits for
a portable device to attach to the USB socket.
9. Attach a CDP compliant portable device to the type A
socket of the DC2688A demo board.
10. Observe the CDP negotiation between the porta-
ble device and the computer. You may monitor the
voltage waveforms on STATUS, V
BUS
, IMON point,
D+, and D– during this CDP negotiation. Observe the
USB data connection between portable device and
the PC as manifested by the portable device showing
up in the PC in “devices and driver” or “this PC”,
and the PC may be able to access data stored in the
portable device.
11. To restart another CDP session, perform the
following steps:
a. Unplug the portable device from the type A socket.
b. Place the JP1 EN jumper to OFF position and then
place it back to ON position. Cycling the EN/UV pin
of the LT8698S/LT8698S-1 resets the CDP state
machine which is necessary in order to restart
another CPD sequence. Alternatively, the CDP state
machine can be reset by setting LT868S to a non-
CDP state (any select state other than state 0, state
1, and state 2) and coming back to state 0 or state
1. Note: in an actual CDP application, a USB host
microcontroller can detect a portable device detach
and reset the DP machine by controlling the SEL
pin(s).
c. Repeat from step 8.
QUICK START PROCEDURE
