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Test Summary
17. Verify V
OUT
is within –50 mV of V
BAT
.
18. Remove short betwen J3-4 and J3-3 on UUT. Verify on the scope that V
OUT
does not drop out. Verify
D2 (STAT1) has turned on, charging has resumed and V
OUT
is powered from the input.
19. Disconnect the +5.25-VDC Input Supply from the UUT AC input. Verify on the scope that V
OUT
does
not drop out. Verify V
OUT
is within –50 mV of V
BAT
and D2 (STAT1) and D5 (ACPG) LEDs turn off. This
demonstrates battery power backup for loss of AC adapter.
20. Reapply the +5.25-VDC supply to the UUT AC input. Verify on the scope that V
OUT
does not drop out.
Verify D2 (STAT1) and D5 (ACPG) LEDs turn on.
21. Adjust R15 until the voltage on TP1 is ~ 3.50 VDC (V
BAT
should be less than 3.9 V for this
demonstration; otherwise, discharge battery).
22. Reduce the current limit on the input supply to ~ 1 A (going to AC pin on UUT) and verify on the scope
that V
OUT
has dropped to the VDPPM level of ~4.0 V {(3.5 V at TP1) × 1.15 = 4 V}. Note that the
current into the battery is ~ 600 mA (1-A input minus 400 mA to the system), which has been reduced
to keep the output from falling below the programmed DPPM OUTPUT threshold of 4 V. This
demonstrates DPPM operation (charging current to the battery is reduced if output drops to the DPPM
OUTPUT voltage threshold attempting to keep the output voltage from dropping further).
23. Further reduce the input’s current limit to 250 mA. Verify on the scope that V
OUT
does not drop out.
Verify that V
OUT
drops just below V
BAT
(< 50 mV). Because the available input current is less than the
system OUT load, reducing the battery charging current to zero is still not enough reduction in load to
keep the output from dropping. Once the output drops below ~ 50 mV, the internal battery FET turns
on and allows the battery to source the OUT pin system load. This demonstrates battery supplement
mode.
24. Return the current limit of the +5.25-V supply to ~2 A. Verify V
OUT
returns to Vreg or Vin (see Step 8 of
this test procedure).
25. Set JMP2 (PSEL) to USB (PSEL = low). Verify that the input current (AC) drops to between 400 mA
and 500 mA. The programmed charge current of ~1 A and the system load of 10
Ω
exceeds the USB
0.5-A limit; therefore,V
OUT
drops until the DPPM OUTPUT voltage threshold, or battery voltage, is
reached (which ever is higher). If the DPPM OUTPUT threshold is larger, the charging current is
reduced to keep the output voltage from dropping further. If the battery voltage is higher, the battery
supplements the current to keep the output from dropping too much (50 mV to 200 mV) below the
battery voltage. Note that setting PSEL to low (USB mode; PSEL high is AC mode) selects the USB
input as the primary source. If the USB source is not present, and the ac source is present, the IC
uses the AC input source as if it were a USB input. This feature is useful if only one input power
connector is desired, and two sources (USB and AC adaptor) are available. A keyed cable or a
u-controller would set the PSEL pin for the available source. Note that the system would ideally go to a
lower power mode prior to selecting USB operation to avoid pulling down V
OUT
.
26. Plug in a USB cable from a high-power port (500 mA) into the UUT (or supply 5 VDC to J1). Verify that
the USB input now supplies the input current instead of the AC (J2) input. This demonstrates that
JMP2 (PSEL) defines the priority of the inputs. If PSEL = Low (USB priority), then the USB input is
used first, if available, and if not it switches to AC power at USB-current levels.
27. Verify that D4 (USBPG) turns on.
28. Set JMP2 (PSEL) to AC, and verify that the AC supply is providing ~1.5 A of current (~0.44 to the load
and 1 A to the battery plus miscellaneous).
29. Remove the ac-input supply and verify that the USB source is supplying between 400 mA and 500 mA
of current to the input. The output should have dropped to the DPPM OUTPUT threshold or battery
voltage (whichever is higher).
30. Verify that D5 (ACPG) turns off.
31. Reapply the AC-input source and verify that the AC source is now providing the ~1.5 A as before.
32. Verify that D5 (ACPG) turns on.
33. Set JMP2 (PSEL) to USB, and verify that the USB source is now providing between 400 mA and 500
mA of current.
34. Set JMP1 to 0.1 on the UUT. Verify that the input current has dropped below 100 mA and V
OUT
has
dropped slightly below V
BAT
. In this test, the system load is 10
Ω
, which would result in the output
dropping to 1 V at 100 mA if there were no other source to help out. As the output voltage drops to the
DPPM OUTPUT threshold, the charging current is reduced to zero, but V
OUT
continues to drop until it
reaches the battery voltage. The internal battery FET turns on to supplement the OUTPUT. This
SLUU207A – October 2004 – Revised January 2007
bq2403x (bqTiny-III™) 1.5-A Single-Chip Li-Ion
5
and Li-Pol Charge Management IC EVM
