Linear Technology DC1920A Demo Manual

Li-Ion Charger, Always-On LDO and Buck Regulator
DESCRIPTION
Demonstration circuit DC1920A is a micropower USB
power manager with Li-ion charger, buck DC/DC, and
always-on LDO regulator featuring the LTC
PERFORMANCE SUMMARY
SYMBOL PARAMETER
VBUS Bus Input Voltage Range
V(BAT) Battery Float Voltage
I(BAT) Battery Charge Current
VLDO LDO Output Voltage
VBUCK Buck Regulator Output Voltage
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. Application of power to BAT
(PS2), causes a POR. As shown in Figure 5 of the data
sheet, the POR causes the LTC3553EUD-2 to enter the
PDN1 state. In the PDN1 state VLDO is on, and VBUCK
is off. After 1s, the LTC355EUD-2 transitions to the Hard
Reset (HR) state. In HR VLDO is off, and total current
draw from the battery is less than 1μA.
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DEMO MANUAL DC1920A
Micropower USB Power Manager with
Design files for this circuit board are available at
http://www.linear.com/demo
® 3553EUD-2.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
(T = 25°C)
A
CONDITIONS
Constant Voltage Mode
Constant Current Mode, RPROG = 1.87k
I(VLDO) ≤ 150mA
I(VBUCK) ≤ 200mA
2. Press "REGS ON" button for > 0.5 seconds. Observe
LTC3553EUD-2
MIN
4.35
4.15
380
3.25
1.15
I(BAT) (AM2), VBUCK (VM5) and VLDO (VM6). Press-
ing the "REGS ON" button for > 0.5 seconds causes
the LTC3553EUD-2 to enter the PUP1 state. In the
PUP1 state both regulators are on. After 5 seconds,
the LTC3553EUD-2 enters the PON state. Observe
VLDO (VM6). VLDO is always-on, and is 3.3V. The
LTC3553EUD-2 is in standby mode which reduces
the battery current to less than 15μA, even with both
regulators running. In standby mode the maximum
current from the buck regulator is reduced to 10mA.
Since BUCK_ON (pin 7) on the LTC3553EUD-2 is pulled
up by the buck output, the buck regulator will remain
on, and at 1.2V.
MAX UNITS
5.5 V
4.23 V
420 mA
3.35 V
1.25 V
dc1920af
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