MAX1565ETJ-T Maxim Integrated Products, MAX1565ETJ-T Datasheet - Page 21

• Manufacturer Part Number: MAX1565ETJ-T
• Description: DC/DC Switching Converters 5Ch Digital Camera Power Supply
• Manufacturer: Maxim Integrated Products

When the inductor current falls to zero on each switching
cycle, it is described as discontinuous. The inductor is
not utilized as efficiently as with continuous current. This
often has little negative impact in light-load applications
since the coil losses may already be low compared to
other losses. A benefit of discontinuous inductor cur-
rent is more flexible loop compensation and no maxi-
mum duty-cycle restriction on boost ratio.
To ensure discontinuous operation, the inductor must
have a sufficiently low inductance to fully discharge on
each cycle. This occurs when:
A discontinuous current boost has a single pole at:
Choose the integrator capacitor such that the unity-gain
crossover (f
many auxiliary circuits, such as those powering motors,
LEDs, or other loads that do not require fast transient
response, it is often acceptable to overcompensate by
setting f
where K = 2 L f
slope compensation voltage ramp of 1.25V. The C
zero is then used to cancel the f
Continuous inductor current can sometimes improve
boost efficiency by lowering the ratio between peak
inductor current and output current. It does this at the
expense of a larger inductance value that requires larger
size for a given current rating. With continuous inductor
current boost operation, there is a right-plane zero at:
where (1 - D) = V
plex pole pair is located at:
If the zero due to the output capacitor capacitance and
ESR is less than 1/10 the right-plane zero:
L < [V
R
f
C
C
P
C
Z
C
= (2V
at f
COUT
= R
IN
= [2V
C
2
f
OSC
f
) occurs at f
0
[V
(g
LOAD
RHPZ
(V
= V
OUT
OUT
M
= 1/(2π C
OUT
OSC
OUT
/20 or lower. C
IN
/(2π f
OUT
______________________________________________________________________________________
C
/V
= (1 - D)
- V
/(K(V
- V
OUT
/R
V
OUT
Discontinuous Inductor Current
IN
/[2π V
IN
LOAD,
C
IN
)/(2π R
))]
V
/((2V
Continuous Inductor Current
OUT
)/V
OUT
OSC
(in a boost converter). A com-
OUT
2
OUT 3
IN
Small, High-Efficiency, Five-Channel
and V
R
OUT
/10 or lower. Note that for
R
- V
/[(2V
(L C
LOAD
LOAD
C
ESR
P
IN
] [R
is then determined by:
pole, so:
- V
Digital Still Camera Power Supply
))]
OUT
OUT
) < f
RAMP
C
LOAD
IN
1/2
/(2πL)
OUT
)V
)
RHPZ
- V
1/2
[(V
RAMP
is the internal
/(2 f
IN
V
]
FB
OUT
) C
/10
/V
OSC
)]
C
OUT
)
]
)]
)
C
R
C
Choose C
occurs at Z
at crossover.
Choose R
f
If Z
ceramic output capacitors) and continuous conduction is
required, then cross the loop over before f
In that case:
Place 1/(2π R
R
continuous operation.
Any auxiliary channel can be used for a wide variety of
step-up applications. These include generating 5V or
some other voltage for motor or actuator drive, generating
15V or a similar voltage for LCD bias, or generating a
step-up current source to efficiently drive a series array
of white LEDs for display backlighting. Figures 5 and 6
show examples of these applications.
Figure 5. Using an AUX_ Controller Channel to Generate LCD
Bias
0
LOAD
to cancel one of the pole pairs:
COUT
LED, LCD, and Other Boost Applications
C
C
100mA
C
C
= (V
15V
C
OUT
22µF
C
is not less than f
= (V
C
COUT
R
to place the integrator zero, 1/(2π R
IN
TO V
C
f
/C
such that the crossover frequency f
C
C
/V
IN
= V
C
C
Applications Information
BATT
< f
RAMP
. The ESR zero provides a phase boost
/V
C
4.7µF
or reduce the inductor value for dis-
) = 1/(2π R
IN
0
RAMP
/10, and f
(L C
1.1MΩ
100kΩ
)(V
)(V
FB
OUT
/V
FB
RHPZ
4.7µH
OUT
C
)
/V
LOAD
1/2
< f
OUT
/(V
/10 (as is typical with
)(g
DL_
FB_
RHPZ
C
)(g
OUT
M
OUT
(PARTIAL)
MAX1565
OUTSU
/(2π Z
M
/10
C
), so that R
/(2π f
RHPZ
C
AUX_
PWM
)
COUT
C
and f
))
C
C
))
C
0
), at
C
:
21
C
=