MAX1965TEEP Maxim Integrated, MAX1965TEEP Datasheet - Page 19

• Manufacturer Part Number: MAX1965TEEP
• Description: Current & Power Monitors & Regulators
• Manufacturer: Maxim Integrated

I
equals twice the output voltage (V
I
lum capacitors (ceramic, aluminum, polymer, or OS-
CON) are preferred due to their robustness with high
inrush currents typical of systems with low impedance
inputs. Additionally, two (or more) smaller value low-
ESR capacitors can be connected in parallel for lower
cost. Choose an input capacitor that exhibits less than
+10°C temperature rise at the RMS input current for
optimal circuit long-term reliability.
The key selection parameters for the output capacitor
are the actual capacitance value, the equivalent series
resistance (ESR), and voltage-rating requirements
which affect the overall stability, output ripple voltage,
and transient response.
The output ripple has two components: variations in the
charge stored in the output capacitor, and the voltage
drop across the capacitor’s equivalent series resis-
tance (ESR) caused by the current into and out of the
capacitor.
The output voltage ripple as a consequence of the ESR
and output capacitance is:
where I
Inductor Selection section). These equations are suit-
able for initial capacitor selection, but final values
should be set by testing a prototype or evaluation cir-
cuit. As a general rule, a smaller ripple current results in
less output ripple. Since the inductor ripple current is a
factor of the inductor value and input voltage, the out-
put voltage ripple decreases with larger inductance,
but increases with lower input voltages.
With low-cost aluminum electrolytic capacitors, the
ESR-induced ripple can be larger than that caused by
the charge into and out of the capacitor. Consequently,
RMS
RMS(MAX)
has a maximum value when the input voltage
p-p
V
I
= I
RIPPLE
RMS
is the peak-to-peak inductor current (see
LOAD
I
V
V
P P
RIPPLE ESR
RIPPLE C
-
=
I
= V
LOAD
______________________________________________________________________________________
=
/2. For most applications, nontanta-



RIPPLE(ESR) +
V
(
( )
IN
ƒ
-
SW
=
Tracking/Sequencing Triple/Quintuple
V
V
)
OUT IN
OUT
8
=
L
C
I
P P
OUT SW
-
(
I
V
P P



V
ESR
-



IN
V
ƒ
−
V
OUT
V
IN
V
RIPPLE(C)
Output Capacitor
OUT
IN



= 2V
)
OUT
), so
Power-Supply Controllers
high quality low-ESR aluminum-electrolytic, tantalum,
polymer, or ceramic filter capacitors are required to
minimize output ripple. Best results at reasonable cost
are typically achieved with an aluminum-electrolytic
capacitor in the 470µF range, in parallel with a 0.1µF
ceramic capacitor.
Since the MAX1964/MAX1965 use a current-mode con-
trol scheme, the output capacitor forms a pole that
affects circuit stability (see Compensation Design).
Furthermore, the output capacitor’s ESR also forms a
zero.
The MAX1964/MAX1965’s response to a load transient
depends on the selected output capacitor. After a load
transient, the output instantly changes by ESR x
∆I
will sag further depending on the inductor and output
capacitor values. After a short period of time (see
Typical Operating Characteristics), the controller
responds by regulating the output voltage back to its
nominal state. For applications that have strict transient
requirements, low-ESR high-capacitance electrolytic
capacitors are recommended to minimize the transient
voltage swing.
Do not exceed the capacitor’s voltage or ripple-current
ratings.
The MAX1964/MAX1965 controllers use an internal
transconductance error amplifier whose output allows
compensation of the control loop. Connect a series
resistor and capacitor between COMP and GND to
form a pole-zero pair, and connect a second parallel
capacitor between COMP and GND to form another
pole. The external inductor, high-side MOSFET, output
capacitor, compensation resistor, and compensation
capacitors determine the loop stability. The inductor
and output capacitor are chosen based on perfor-
mance, size, and cost, while the compensation resistor
and capacitors are selected to optimize control-loop
stability. The component values shown in the Standard
Application Circuit (Figures 1 and 6) yield stable opera-
tion over a broad range of input-to-output voltages.
The controller uses a current-mode control scheme that
regulates the output voltage by forcing the required
current through the external inductor, so the
MAX1964/MAX1965 use the voltage across the high-
side MOSFET’s on-resistance (R
inductor current. Using the current-sense amplifier’s
output signal and the amplified feedback voltage, the
control loop determines the peak inductor current by:
LOAD
. Before the controller can respond, the output
Compensation Design
DS(ON)
) to sense the
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