MAX17015 Maxim Integrated Products, MAX17015 Datasheet - Page 17

• Manufacturer Part Number: MAX17015
• Description: (MAX17005 - MAX17015) High-Performance Chargers
• Manufacturer: Maxim Integrated Products

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Figure 7. CC Loop Diagram
The simplified schematic in Figure 7 is sufficient to
describe the operation of the controller’s voltage loop,
CC. The required compensation network is a pole-zero
pair formed with C
to compensate the pole formed by the output capacitor
and the load. R
(ESR) of the charger output capacitor (C
equivalent charger output load, where R
ΔI
amplifier, R
amplifier transconductance, GMV = 0.125μA/mV. The
DC-DC converter transconductance is dependent upon
charge current-sense resistor RS2:
Table 2. CC Loop Poles and Zeros
CCV Pole
CCV Zero
CHG
NAME
Output
Output
Zero
Pole
R
C
. The equivalent output impedance of the GMV
CC
CC
CC
OGMV
f
f
P CV
Z OUT
R
f
f
P OUT
ESR
OGMV
_
Z CV
_
, is greater than 10MΩ. The voltage-
_
_
______________________________________________________________________________________
CC
GM
is the equivalent series resistance
OUT
=
GMV
and R
=
EQUATION
=
2π
=
2π
2π
R
2π
OGMV
R
R
R
CC
ESR
CC
L
VCTL
CC Loop Compensation
1
1
×
. The zero is necessary
1
1
×
×
C
×
C
C
OUT
C
CC
OUT
BATT
CC
C
R
OUT
ESR
OUT
L
). R
= ΔV
Lowest frequency pole created by C
Voltage-loop compensation zero. If this zero is at the same frequency or lower
than output pole f
response near the crossover frequency. Choose C
least one decade below crossover to ensure adequate phase margin.
Output pole formed with the effective load resistance R
capacitance C
of the system or the crossover frequency.
Output ESR Zero. This zero can keep the loop from crossing unity gain if
f
capacitor with an ESR zero greater than the crossover frequency.
Z_OUT
L
High-Performance Chargers
BATT
is the
is less than the desired crossover frequency; therefore, choose a
R
L
/
OUT
where A
cation circuits, so GM
The loop transfer function is given by:
The poles and zeros of the voltage-loop transfer function
are listed from lowest frequency to highest frequency in
Table 2.
Near crossover, C
R
nates the parallel impedance near crossover. Additionally,
R
the series combination of R
C
crossover so the parallel impedance is mostly capaci-
tive and:
P_OUT
. R
OGMV
CC
OUT
L
is much higher impedance than C
influences the DC gain but does not affect the stability
, the loop-transfer function approximates a single-pole
is also much lower impedance than R
. Since C
LTF
CSI
×
=
R
1.2MHz Low-Cost,
= 20, and RS2 = 10mΩ in the typical appli-
DESCRIPTION
OGMV
(
GM
(1
1
+
(
(
+
1
1
CC
GM
sC
+
CV
OUT
sC
+
sC
sC
CC
CC
× +
is in parallel with R
and GMV’s finite output resistance.
OUT
OUT
(
CC
OUT
×
OUT
R
1
×
is much lower impedance than
L
R
×
R
L
×
sC
=
OGMV
R
CC
×
= 5A/V.
R
×
ESR
CC
OGMV
R
A
GMV R
L
CSI
and C
CV
)
×
) ) (
≅
)(
1
1
×
R
to place this zero at
1
×
+
)
sC
CC
L
RS
+
sC
CC
and the output
sC
OGMV
OUT
1
2
)
CC
CC
, so:
OGMV,
≅
OUT
R
×
and dominates
CC
R
×
CC
R
C
L
CC
)
)
L
domi-
near
17