Datasheet
LTC4099
15
4099fd
operaTion
+
–
+
+
–
0.3V
1.18V 3.6V
CLPROG
I
SWITCH
/N
+
–
+
–
15mV
OmV
IDEAL
DIODE
PWM AND
GATE DRIVE
AVERAGE INPUT
CURRENT LIMIT
CONTROLLER
AVERAGE OUTPUT
VOLTAGE LIMIT
CONTROLLER
CONSTANT-CURRENT
CONSTANT-VOLTAGE
BATTERY CHARGER
+
–
19
IDGATE
10
V
OUT
12
SW
3.5V TO
(BAT + 0.3V)
TO SYSTEM
LOAD
OPTIONAL
EXTERNAL
IDEAL DIODE
PMOS
SINGLE-CELL
Li-Ion
4099 F01
14
BAT
11
BATSENS
FROM USB
OR WALL
ADAPTER
13
+
1
OVGATE
V
BUS
OVSENS
TO AUTOMOTIVE,
FIREWIRE, ETC.
ACPR
BAT + 0.3V
3.6V
V
OUT
4.3V
+
+
–
+
–
18
WALL
Bat-Track HV CONTROL
5
V
C
4
SW
FB
HV
IN
V
C
HIGH VOLTAGE
STEP-DOWN
SWITCHING
REGULATOR
6
s2
6V
OVERVOLTAGE PROTECTION
+
–
+–
20
When the switching regulator is activated, the average
input current will be limited by the CLPROG programming
resistor according to the following expression:
I
VBUS
=I
VBUSQ
+
V
CLPROG
R
CLPROG
• h
CLPROG
+1
( )
where I
VBUSQ
is the quiescent current of the LTC4099,
V
CLPROG
is the CLPROG servo voltage in current limit,
R
CLPROG
is the value of the programming resistor and
h
CLPROG
is the ratio of the measured current at V
BUS
to the
sample current delivered to CLPROG. Refer to the Electri-
cal Characteristics
table for values of h
CLPROG
, V
CLPROG
and I
VBUSQ
. Given worst-case circuit tolerances, the USB
specification for the average input current in 100mA or
500mA mode will not be violated, provided that R
CLPROG
is 3.01k or greater. See Table 2 for other available settings
of input current limit.
While not in current limit, the switching regulator’s
Bat-Track feature will set V
OUT
to approximately 300mV
above the voltage at BAT. However, if the voltage at BAT is
below 3.3V
, and the load requirement does not cause
the switching regulator to exceed its current limit, V
OUT
will regulate at a fixed 3.6V, as shown in Figure 2. This
instant-on feature will allow a portable product to run
immediately when power is applied without waiting for
Figure 1. PowerPath Block Diagram
BAT (V)
2.4
4.5
4.2
3.9
3.6
3.3
3.0
2.7
2.4
3.3 3.9
4099 F02
2.7 3.0
3.6 4.2
V
OUT
(V)
NO LOAD
300mV
Figure 2. V
OUT
vs BAT