isl88731a Intersil Corporation, isl88731a Datasheet - Page 20

no-image

isl88731a

Manufacturer Part Number
isl88731a
Description
Smbus Level 2 Battery Charger
Manufacturer
Intersil Corporation
Datasheet

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
isl88731aHRZ
Manufacturer:
TI
Quantity:
190
Part Number:
isl88731aHRZ
Manufacturer:
INTERSIL
Quantity:
20 000
Part Number:
isl88731aHRZ-T
Manufacturer:
INTERSIL
Quantity:
8 000
The loop response equations, bode plots and the selection
of C
with loop gain reduced by the duty cycle and the ratio of
R
D = 50%, the loop gain will be 6dB lower than the loop gain
in Figure 23. This gives lower crossover frequency and
higher phase margin in this mode. If R
duty cycle is 50% then the adapter current loop gain will be
identical to the gain in Figure 23.
A filter should be added between R
reduce switching noise. The filter roll off frequency should be
between the crossover frequency and the switching
frequency (~100kHz).
Voltage Control Loop
When the battery is charged to the voltage set by
DCIN
S1
FIGURE 23. ADAPTER CURRENT LIMIT CONTROL LOOP
ICOMP
/R
FIGURE 22. CHARGE CURRENT LOOP BODE PLOTS
R
-20
-40
-60
C
60
40
20
C
S2
S1
F1
0
ICOMP
0.01
. In other words, if R
ICOMP
are the same as the charge current control loop
CSSN
CSSP
R
F1
S
Σ
0.1
11
+
-
F
20
POLE1
GMS
0.25
CA1
-
+
PHASE
+
-
FREQUENCY (kHz)
1
20
S1
R
FET_RDSON
CA2
DACS
= R
20X
+
-
S1
F
S2
ZERO
10
and CSIP and CSIN to
CSOP
CSON
S1
and the duty cycle
F
F
/R
FILTER
POLE2
L
S2
C
R
Compensator
Modulator
Loop
C
= 2 and the
100
R
F2
ESR
O
L_DCR
R
F2
R
1000
R
S2
BAT
ISL88731A
ChargeVoltage register the voltage error amplifier (GMV)
takes control of the output (assuming that the adapter
current is below the limit set by ACLIM). The voltage error
amplifier (GMV) discharges the capacitor on VCOMP to limit
the output voltage. The current to the battery decreases as
the cells charge to the fixed voltage and the voltage across
the internal battery resistance decreases. As battery current
decreases the two current error amplifiers (GMI and GMS)
output their maximum current and charge the capacitor on
ICOMP to its maximum voltage (limited to 0.3V above
VCOMP). With high voltage on ICOMP, the minimum voltage
buffer output equals the voltage on VCOMP.
The voltage control loop is shown in Figure 24.
Output LC Filter Transfer Functions
The gain from the phase node to the system output and
battery depend entirely on external components. Typical
output LC filter response is shown in Figure 25. Transfer
function A
A
The resistance R
inductor DCR, R
battery (normally between 50mΩ and 200mΩ) The worst
case for voltage mode control is when the battery is absent.
This results in the highest Q of the LC filter and the lowest
phase margin.
The compensation network consists of the voltage error
amplifier GMV and the compensation network R
ω
LC
ESR
VCOMP
=
C
R
=
---------------------------------------------------------- -
VCOMP
VCOMP
----------- -
ω
s
-------------------------------- -
(
DP
R
2
Σ
LC
S
FIGURE 24. VOLTAGE CONTROL LOOP
ESR
(s) is shown in Equation 22:
+
1
1
------------------------ -
(
ω
---------------
ω
11
LC
SENSE
C
O
0.25
ESR
GMV
s
s
o
is a combination of MOSFET r
)
+
-
+
Q
-
DACV
PHASE
)
+
ω
and the internal resistance of the
1
LC
R
CA2
FET_RDSON
=
R4
20x
R3
----------------------- -
(
+
-
L C
1
o
CSOP
CSON
)
L
Q
R
=
L_DCR
C
C
R
R
VCOMP
F2
ESR
O
o
DS(ON)
January 7, 2009
R
F2
(EQ. 22)
------ -
C
FN6738.1
L
o
,
R
R
,
S2
BAT

Related parts for isl88731a