LTC1325 LINER [Linear Technology], LTC1325 Datasheet - Page 14

• Manufacturer Part Number: LTC1325
• Description: Microprocessor-Controlled Battery Management System
• Manufacturer: LINER [Linear Technology]

FUNCTIONAL DESCRIPTIO
rise as does the voltage across the sense resistor. When
the voltage across the sense resistor is greater than the
output of the integrator, comparator A2 changes state.
This resets the flip-flop and P1 is turned off. Catch diode
D1 clamps the drain of P1 one diode drop below ground
when the inductor flies back and the current through the
inductor starts to drop. The voltage across the sense
resistor also drops and may reach zero and stay there until
the next clock cycle begins.
The average charging current is set by the output of the
DAC (V
programmed to one of four values with the following
ratios: 1, 1/3, 1/5 or 1/10. The duty ratio can be set to
1/16, 1/8, 1/4, 1/2 or 1. When the duty ratio is 1, the duty
ratio generator output is always low and the charge loop
operates continuously (see Figure 4). At other duty ratio
settings, the duty generator output is a square wave with
a period of 42 seconds. The time for which the generator
output is low varies with the duty ratio setting. For ex-
LTC1325
14
U
DAC
ADC MUX
DR0 TO
) and the duty ratio generator. V
OSCILLATOR
DR2
Q
U
TO
111kHz
S
R
3
GG
0
0
0
0
1
VR1
GENERATOR
DUTY RATIO
0
0
1
1
X
ONE SHOT
VR0
0
1
0
1
X
A2
DAC VOLTAGE
160mV
18mV
34mV
55mV
CHARGE
+
–
0mV
U
Figure 4. Charging Loop Block Diagram
16pF
C1
DAC
A1
GG
can be
–
+
V
S1
DAC
500k
R1
S2
S3
VR0, VR1
ample, if a duty ratio of 1/2 is programmed, the generator
output is low only for 42/2 = 21 seconds. Since the loop
operates for only 21 out of every 42 seconds, the average
charging current is halved. In general, the average charg-
ing current is:
Gated PFET Controller
When using an external current regulator or current lim-
ited wall pack, simply remove the inductor L1 and catch
diode D1. Set the DAC control bits VR1 = 1 and VR0 = 1,
and select the desired duty ratio. By insuring that the
voltage at the Sense pin is never greater than 140mV, the
output of the integrator A1 will saturate high and the
comparator A2 will never trip and turn the loop off. This
can be achieved by removing the sense resistor and
grounding the Sense pin or if the gas gauge is to be used,
selecting R
DISCHARGE
125k
2
I
3.072V
DAC
R2
CHRG
REG
(GAS GAUGE)
= V
R
1k
S4
F
SENSE
GG
DAC
(Duty Ratio)/R
BOUNDARY
so that R
CHIP
PGATE
DIS
SENSE
FILTER
BATTERY
SENSE
4.5V TO 16V
C
L1
F
SENSE
V
DD
/I
R
P1
IRF9Z30
CHRG
SENSE
D1
1N5818
IRFZ34
< 140mV.
N1
LTC1325 • F04
R
R
TRK
DIS