1
DESCRIPTION
Demonstration Circuit DC1550A is a Micropower USB Power Manager with Li-Ion Charger, Buck DC/DC, and LDO
Regulator featuring the LTC
®
3553.
PERFORMANCE SUMMARY
Specifications are at T
A
= 25°C
SYMBOL PARAMETER
CONDITIONS
MIN TYP
MAX
UNITS
VBUS
Bus Input Voltage Range
4.35
6
V
V(BAT)
Battery Float Voltage
Constant Voltage Mode
4.15
4.23
V
I(BAT)
Battery Charge Current
Constant Current Mode, R
PROG
= 1.87k
420
500 mA
VLDO
LDO Output Voltage
I(VLDO) ≤ 200mA
3.25
3.35
V
VBUCK
Buck Regulator Output Voltage
I(VBUCK) ≤ 200mA
1.15
1.25
V
QUICK START PROCEDURE
Refer to Figure 1 for the proper measurement
equipment setup and jumper settings and follow the
procedure below.
NOTE.
When measuring the input or output voltage ripple, care
must be taken to avoid a long ground lead on the oscilloscope
probe. Measure the input or output voltage ripple by touching the
probe tip directly across the VBUS or VOUT(x) and GND terminals.
See Figure 2 for proper scope probe technique.
1.
Set PS1 = 0V, PS2 = 3.6V. Press “ON” button
for > 0.5s. Observe I(BAT) (AM2), VBUCK
(VM5) and VLDO (VM6).
The LTC3553 is in STBY which reduces the bat-
tery current to less than 15μA, even with both
regulators running. In STBY the maximum cur-
rent from regulators is reduced to as low as
10mA
2.
Set STBY (JP6) to “OFF”, PS1 to 5V. Observe
I(VBUS) (AM1), I(BAT) (AM2) and VPROG
(VM2).
The LTC3553 is now operating in normal mode
drawing more current from the battery. However
the regulators are now capable of delivering over
200mA each. Also, since VBUS is now available,
the battery charger is operating, but charge cur-
rent is limited by the input current limit to
100mA.
3.
Set HPWR (JP2) to “500mA”. Observe I(VBUS)
(AM1), I(BAT) (AM2) and VPROG (VM2).
The input current limit is now 500mA, so the bat-
tery charger is delivering ~420mA to the battery.
4.
Set LD2 to 200mA, LD3 to 200mA. Observe
VBUCK (VM5), VLDO (VM6) and I(BAT) (AM2).
Each regulator is supplying 200mA, and since
the efficiency is ~90%, drawing ~225mA. So,
the battery charger is only delivering approxi-
mately 50mA. This is because the input current
limit is 500mA – 225mA – 225mA = 50mA.
QUICK START GUIDE FOR
DC1550A
LTC3553EPD: Micropower USB
Power Manager with Li-Ion Charger,
Buck DC/DC, and LDO Regulator
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