Datasheet

4
LT1505
1505fc
Note 6: See “Lithium-Ion Charging Completion” in the Applications
Information Section.
Note 7: Tested with Test Circuit 3.
Note 8: I
SPIN
keeps switching on to keep V
BAT
regulated when battery is
not present to avoid high surge current from C
OUT
when battery is
inserted.
Note 9: Above undervoltage threshold switching is enabled.
Note 10: Do not connect V
CC
directly to V
IN
(see Figure 1). This connection
will cause the internal diode between V
BAT
and V
CC
to be forward-biased
and may cause high current to flow from V
IN
. When the adapter is
removed, V
CC
will be held up by the body diode of M1.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Tested with Test Circuit 1.
Note 3: Tested with Test Circuit 2.
Note 4: When V
CC
and battery voltage differential is low, high duty factor
is required. The LT1505 achieves a duty factor greater than 99% by
skipping cycles. Only when V
BOOST
drops below the comparator A2
threshold will TGATE be turned off. See Applications Information.
Note 5: When the system starts, C2 (boost cap) has to be charged up to
drive TGATE and to start the system. The LT1505 will keep TGATE off and
turn BGATE on for 0.2µs at 200kHz to charge up C2. Comparator A2
senses V
BOOST
and switches to the normal PWM mode when V
BOOST
is
above the threshold.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 18V, V
BAT
= 12.6V, V
CLN
= V
CC
(LT1505), no load on any
outputs unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Voltage Amplifier VA
Transconductance (Note 3) Output Current from 50µA to 500µA 0.21 0.6 1.0 mho
Output Source Current V
FB
= V
PROG
= V
REF
+ 10mV 1.1 mA
V
FB
Input Bias Current At 0.5mA VA Output Current, T
A
< 70°C –10 25 nA
(3 CELL, 4.1V, 4.2V Are Not Connected, V
BAT2
= 0V)
Current Limit Amplifier CL1
Turn-On Threshold 0.5mA Output Current 87 92 97 mV
Transconductance Output Current from 50µA to 500µA 0.5 1 3 mho
CLP Input Current 0.5mA Output Current 1 3 µA
CLN Input Current 0.5mA Output Current 0.8 2 mA
Input P-Channel FET Driver (INFET)
INFET “On” Clamping Voltage (V
CC
– V
INFET
)V
CC
≥ 11V ● 6.5 7.8 9 V
INFET “On” Driver Current V
INFET
= V
CC
– 6V ● 820 mA
INFET “Off” Clamping Voltage (V
CC
– V
INFET
)V
CC
Not Connected, I
INFET
< –2µA 1.4 V
INFET “Off” Drive Current V
CC
Not Connected, (V
CC
– V
INFET
) ≥ 2V –2.5 mA
Charging Completion Flag (Comparator E6)
Charging Completion Threshold (Note 6) Measured at V
RS1
, V
CAP
= 2V (Note 7) 14 20 28 mV
Threshold On CAP Pin Low to High Threshold ● 3.3 4.2 V
High to Low Threshold
● 0.6 V
V
CAP
at Shutdown V
SHDN
= Low (Shutdown) ● 0.13 0.3 V
FLAG (Open Collector) Output Low V
CAP
= 4V, I
FLAG
< 1mA ● 0.3 V
FLAG Pin Leakage Current V
CAP
= 0.6V ● 3 µA
Gate Drivers (TGATE, BGATE)
V
GBIAS
11V < V
CC
< 24V, I
GBIAS
≤ 15mA ● 8.4 9.1 9.6 V
V
SHDN
= Low (Shutdown) ● 13 V
V
TGATE
High (V
TGATE
– V
SW
)I
TGATE
≤ 20mA, V
BOOST
= V
GBIAS
– 0.5V ● 5.6 6.6 V
V
BGATE
High I
BGATE
≤ 20mA ● 6.2 7.2 V
V
TGATE
Low (V
TGATE
– V
SW
)I
TGATE
≤ 50mA ● 0.8 V
V
BGATE
Low I
BGATE
≤ 50mA ● 0.8 V
Peak Gate Drive Current 10nF Load 1 A
Gate Drive Rise and Fall Time 1nF Load 25 ns
V
TGATE
, V
BGATE
at Shutdown V
SHDN
= Low (Shutdown) ● 1V
I
TGATE
= I
BGATE
= 10µA