isl6252a Intersil Corporation, isl6252a Datasheet - Page 18

• Manufacturer Part Number: isl6252a
• Description: Highly Integrated Battery Charger Controller For Notebook Computers
• Manufacturer: Intersil Corporation

Table 2 shows the component lists for the typical application
circuit in Figure 2.
Loop Compensation Design
ISL6252 has three closed loop control modes. One controls
the output voltage when the battery is fully charged or
absent. A second controls the current into the battery when
charging and the third limits current drawn from the adapter.
The charge current and input current control loops are
compensated by a single capacitor on the ICOMP pin. The
voltage control loop is compensated by a network on the
VCOMP pin. Descriptions of these control loops and
guidelines for selecting compensation components will be
given in the following sections. Which loop controls the
output is determined by the minimum current buffer and the
minimum voltage buffer shown in Figure 1. These three
loops will be described separately.
C
C
C
R
PARTS
2
3
Q
, C
, C
1
8
R
R
R
C
1
Q
C
C
D
D
R
R
R
R
R
R
R
R
, C
, R
L
, Q
10
12
13
11
4
7
5
6
1
2
6
1
2
3
4
5
6
7
9
, C
, C
10
11
2
8
9
10μF/25V ceramic capacitor, Taiyo Yuden
TMK325 MJ106MY X5R (3.2mmx2.5mmx1.9mm)
0.1μF/50V ceramic capacitor
1μF/10V ceramic capacitor, Taiyo Yuden
LMK212BJ105MG
10nF ceramic capacitor
6.8nF ceramic capacitor
3300pF ceramic capacitor
30V/3A Schottky diode, EC31QS03L (optional)
100mA/30V Schottky Diode, Central Semiconductor
10μH/3.8A/26mΩ, Sumida, CDRH104R-100
30V/35mΩ, FDS6912A, Fairchild
Signal N-Channel MOSFET, 2N7002
40mΩ, ±1%, LRC-LR2512-01-R040-F, IRC
20mΩ, ±1%, LRC-LR2010-01-R020-F, IRC
18Ω, ±5%, (0805)
2.2Ω, ±5%, (0805)
100kΩ, ±5%, (0805)
4.7k, ±5%, (0805)
100Ω, ±5%, (0805)
130k, ±1%, (0805)
10.2kΩ, ±1%, (0805)
4.7Ω, ±5%, (0805)
20kΩ, ±1%, (0805)
1.87kΩ, ±1%, (0805)
TABLE 2. COMPONENT LIST
PART NUMBERS AND MANUFACTURER
18
ISL6252, ISL6252A
TRANSCONDUCTANCE AMPLIFIERS GM1, GM2 AND
GM3
ISL6252 uses several transconductance amplifiers (also
known as gm amps). Most commercially available op amps
are voltage controlled voltage sources with gain expressed
as A = V
sources with gain expressed as gm = I
appear in some of the equations for poles and zeros in the
compensation.
PWM GAIN F
The Pulse Width Modulator in the ISL6252 converts voltage
at VCOMP to a duty cycle by comparing VCOMP to a
triangle wave (duty = VCOMP/V
filter formed by L and C
output voltage (Vo = V
wave amplitude is proportional to V
amplitude proportional to DCIN makes the gain from
VCOMP to the PHASE output a constant 11 and is
independent of DCIN. For small signal AC analysis, the
battery is modeled by it’s internal resistance. The total output
resistance is the sum of the sense resistor and the internal
resistance of the MOSFETs, inductor and capacitor.
Figure 18 shows the small signal model of the pulse width
modulator (PWM), power stage, output filter and battery.
In most cases the Battery resistance is very small (<200mΩ)
resulting in a very low Q in the output filter. This results in a
frequency response from the input of the PWM to the
inductor current with a single pole at the frequency
calculated in Equation 29:
f
POLE1
V
INPUT
GAIN = 11
PWM
RAMP
PWM
RAMP GEN
INPUT
PWM
=
OUT
= VDD/11
11
(
------------------------------------------------------------------------------------------------------ -
FIGURE 18. SMALL SIGNAL AC MODEL
R
SENSE
/V
R FET_r
+
-
M
IN
.gm amps are voltage controlled current
+
DS(ON)
r
DS ON
DCIN
O
(
2π L
convert the duty cycle to a DC
*duty). In ISL6252, the triangle
L
⋅
)
+
R
VDD
PP RAMP
R L_DCR
DCR
DCIN
+
OUT
R
. Making the ramp
R SENSE
BAT
L
). The low-pass
R
ESR
/V
CO
)
IN
CO
.gm will
July 19, 2007
(EQ. 29)
FN6498.1
R BAT