LTC4080EDD#TRPBF Linear Technology, LTC4080EDD#TRPBF Datasheet - Page 14

• Manufacturer Part Number: LTC4080EDD#TRPBF
• Description: IC CHARGER LI-ION 10-DFN
• Manufacturer: Linear Technology

Specifications of LTC4080EDD#TRPBF

• Function: Charge Management
• Battery Type: Lithium-Ion (Li-Ion)
• Voltage - Supply: 3.75 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-WFDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC4080
OPERATIO
nominal value, the regulator wakes up and the inductor
current resumes swinging between I
output capacitor recharges and causes the regulator to
re-enter the SLEEP state if the output load remains light
enough. The frequency of this intermittent burst operation
depends on the load current. That is, as the load current
drops further, the regulator turns on less frequently. Thus
Burst Mode operation increases the effi ciency at light loads
by minimizing the switching and quiescent losses. However,
the output voltage ripple increases to about 2%.
To minimize ripple in the output voltage, the current limits
for both switches in Burst Mode operation are reduced
to about 20% of their values in the constant-frequency
mode. Also the zero current of the synchronous switch
is changed to about 35mA thereby preventing reverse
conduction through the inductor. Consequently, the regu-
lator can only deliver approximately 55mA of load current
while in Burst Mode operation. Any attempt to draw more
load current will cause the output voltage to drop out of
regulation.
Current Limit
To prevent inductor current runaway, there are absolute
current limits (I
the NMOS synchronous switch. These limits are internally
set at 520mA and 700mA respectively for PWM mode. If
the peak inductor current demanded by the error amplifi er
ever exceeds the PMOS I
ignored and the inductor current will be limited to PMOS
I
reduced to 80mA to minimize output voltage ripple.
Zero Current Comparator
The zero or reverse current comparator monitors the induc-
tor current to the output and shuts off the synchronous
rectifi er when this current reduces to a predetermined
value (I
tive 15mA meaning that the regulator allows the inductor
current to fl ow in the reverse direction (from the output to
ground through the synchronous rectifi er) to a maximum
value of 15mA. This is done to ensure that the regulator
is able to regulate at very light loads without skipping any
cycles thereby keeping output voltage ripple and noise low
at the cost of effi ciency.
14
LIM
. In Burst Mode operation, the PMOS current limit is
ZERO
). In fi xed frequency mode, this is set to nega-
LIM
U
) on both the PMOS main switch and
LIM
, the error amplifi er will be
PEAK
and I
ZERO
. The
However, in Burst Mode operation, I
35mA meaning that the synchronous switch is turned off
as soon as the current through the inductor to the output
decreases to 35mA in the discharge cycle. This preserves
the charge on the output capacitor and increases the overall
effi ciency at light loads.
Soft-Start
The LTC4080 switching regulator provides soft-start in
both modes of operation by slowly charging an internal
capacitor. The voltage on this capacitor, in turn, slowly
ramps the current limits of both switches from a low value
to their respective maximum values over a period of about
400μs. The soft-start capacitor is discharged completely
whenever the regulator is disabled.
Short-Circuit Protection
In the event of a short circuit at the output or during
start-up, V
slope of the inductor current is ~V
current may not get a chance to discharge enough to
avoid a runaway situation. Because the current sensing
is blanked for ~12ns at the beginning of each clock cycle,
inductor current can build up to a dangerously high level
over a number of cycles even if there is a hard current
limit on the main PMOS switch. This is why the switching
regulator in the LTC4080 also monitors current through
the synchronous NMOS switch and imposes a hard limit
on it. If the inductor current through the NMOS switch at
the end of a discharge cycle is not below this limit, the
regulator skips the next charging cycle thereby preventing
inductor current runaway.
Switching Regulator Undervoltage Lockout
Whenever V
out circuit keeps the regulator off, preventing unreliable
operation. However, if the regulator is already running
and the battery voltage is dropping, the undervoltage
comparator does not shut down the regulator until V
drops below 2.5V.
OUT
BAT
will be near zero volts. Since the downward
is less than 2.7V, an undervoltage lock-
ZERO
OUT
/L, the inductor
is set to positive
4080fb
BAT