ISL6252 Datasheet, PDF (21/25 Pages) Intersil Corporation – Highly Integrated Battery Charger Controller for Notebook Computers

ISL6252, ISL6252A
20
10
0
-10
-20
-30 _{RBATTERY = 200mΩ}
-40
-50
R_BATTERY = 50mΩ
-60
NO BATTERY
-20
-40
-60
-80
-100
-120
-140
-160
100 200 500 1k 2k 5k 10k 20k 50k 100k 200k 500k
FREQUENCY
FIGURE 23. FREQUENCY RESPONSE OF THE LC OUTPUT
The resistance^FILR^T_O^Ei^Rs a combination of MOSFET r_DS(ON),
inductor DCR, R_SENSE and the internal resistance of the
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 gm1 and the compensation network R_VCOMP,
C_VCOMP, which give the loop very high DC gain, a very low
frequency pole and a zero at f_ZERO1. Inductor current
information is added to the feedback to create a second
zero, f_ZERO2. The low pass filter R_F2, C_F2 between R_SENSE
and ISL6252 add a pole at f_FILTER. R₃ and R₄ are internal
divider resistors that set the DC output voltage. For a 3-cell
battery, R₃ = 320kΩ and R₄ = 64kΩ. Equations 37, 38, 39,
40, 41 and 42 relate the compensation network’s poles,
zeros and gain to the components in Figure 22. Figure 24
shows an asymptotic Bode plot of the DC/DC converter’s
gain vs frequency. It is strongly recommended that f_ZERO1 is
approximately 30% of f_LC and f_ZERO2 is approximately 70%
of f_LC.
COMPENSATOR
MODULATOR
f_LC
f_POLE1
40
LOOP
20
0
-20
f_FILTER
-40
f_ZERO1
f_ZERO2
F_ESR
-60
0.1k
1k
10k
100k
1M
FREQUENCY (Hz)
FIGURE 24. ASYMPTOTIC BODE PLOT OF THE VOLTAGE
CONTROL LOOP GAIN
COMPENSATION BREAK FREQUENCY EQUATIONS
f_ZERO1
=
----------------------------------¹------------------------------------
(2π ⋅ C_VCOMP ⋅ R_1COMP)
(EQ. 37)
f_ZERO2
=
⎛
⎜
⎝
-₂---_π-----_â‹---_R----^R-_S----_EV---_N-^C----_SO----_EM-----_â‹^P---_C----_O-----_U----_T- _{⎠⎟⎞}
⋅
⎛
⎜
⎝
R^-----₄^--R--+---4--R^-----₃^-_{⎠⎟⎞}
⋅ _⎝⎛^g----^m-₅-----¹--_⎠⎞
(EQ. 38)
f_LC
=
---------------¹----------------
(2π L ⋅ C_o)
f_FILTER
=
--------------------¹----------------------
(2π ⋅ R_F2 ⋅ C_F2)
f_POLE1 = ₍---₂----_π-----_â‹---_R----_S----_E--¹--_N----_S----_E-----_â‹---_C-----_o---₎
f_ESR
=
---------------------¹-----------------------
(2π ⋅ C_o ⋅ R_ESR)
(EQ. 39)
(EQ. 40)
(EQ. 41)
(EQ. 42)
21
FN6498.3
August 25, 2010