Datasheet
LTC4000-1
14
40001fa
For more information www.linear.com/LTC4001-1
operaTion
off. While terminated, if the input voltage loop is not in
regulation, the output voltage regulation loop takes over to
ensure that the output voltage at CSP remains in control.
The output voltage regulation loop regulates the voltage
at the CSP pin such that the output feedback voltage at
the OFB pin is 1.193V.
If the system load requires more power than is available
from the input, the battery ideal diode controller provides
supplemental power from the battery. When the battery
voltage discharges below 97.1% of the float voltage
(V
BFB
< V
RECHRG(FALL)
), the automatic recharge feature
initiates a new charge cycle.
Charge Current Regulation
The first loop involved in a normal charging cycle is the
charge current regulation loop (Figure 3). This loop drives
the ITH and CC pins. This loop ensures that the charge
current sensed through the charge current sense resistor
(R
CS
) does not exceed the programmed full charge current.
tor divider does not consume battery current when the
battery is the only available power source. For V
IN
≥ 3V,
the typical resistance from the FBG pin to GND is 100Ω.
Output Voltage Regulation
When charging terminates and the system load is com-
pletely supplied from the
input, the PMOS connected to
BGA
TE is turned off. In this scenario, the output voltage
regulation loop takes over from the battery float voltage
regulation loop (Figure 5). The output voltage regulation
loop regulates the voltage at the CSP pin such that the
output feedback voltage at the OFB pin is 1.193V.
Figure 3. Charge Current Regulation Loop
Figure 4. Battery Float Voltage Regulation Loop with FBG
Figure 5. Output Voltage Regulation Loop with FBG
CSP
CC
1V
A5
ITH
LTC4000-1
CSP CSN
R
IS
BAT PMOS
TO SYSTEM
IBMON
CL
C
IBMON
(OPTIONAL)
C
CSP
+
–
–
+
+
–
–
C
C
TO DC/DC
40001 FO3
R
C
60k
50µA AT NORMAL
5µA AT TRICKLE
BIAS
A9
g
m
= 0.33m
R
CL
CC
1.136V
ITH
LTC4000-1
BFB
BAT
FBG
–
+
C
C
TO DC/DC
40001 FO4
R
C
R
BFB2
R
BFB1
A6
+
–
CC
1.193V
ITH
LTC4000-1
OFB
CSP
FBG
–
+
C
C
TO DC/DC
40001 FO5
R
C
R
OFB2
R
OFB1
A7
+
–
Battery Voltage Regulation
Once the float voltage is reached, the battery voltage regu-
lation loop takes over from the charge current regulation
loop (Figure 4).
The float voltage level is programmed using the feedback
resistor divider between the BAT pin and the FBG pin with
the center node connected to the BFB pin. Note that the
ground return of the resistor divider is connected to the
FBG pin. The FBG pin disconnects the resistor divider
load when V
IN
< 3V to ensure that the float voltage resis-
Battery Instant-On and Ideal Diode
The LTC4000-1 controls the external PMOS connected to
the BGATE pin with a controller similar to the input ideal
diode controller driving the IGATE pin. When not charg-
ing, the PMOS behaves as an ideal diode between the BAT
(anode) and the CSN (cathode) pins. The controller (A2)
regulates the external PMOS to achieve low loss conduc-
tion by driving the gate of the PMOS device such that the
voltage drop from the BAT pin to the CSN pin is 8mV.
When the ability to deliver a particular current with an 8mV
drop across the PMOS source and drain is exceeded, the
voltage at the gate clamps at V
BGATE(ON)
and the PMOS
behaves like a fixed value resistor (R
DS(ON)
).