MAX1565ETJ+T Maxim Integrated Products, MAX1565ETJ+T Datasheet - Page 19

• Manufacturer Part Number: MAX1565ETJ+T
• Description: IC DGTL CAM PWR-SUP 5CH 32TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1565ETJ+T

• Applications: Converter Controller, Digital Cameras
• Voltage - Input: 0.7 ~ 5.5 V
• Number Of Outputs: 5
• Voltage - Output: 3.3V, 1.25 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Choose f
Choose 6.8nF. Now select R
requirements are met. For example, if 4% transient
droop is allowed, the input to the error amplifier moves
0.04 x 1.25V, or 50mV. The error amp output drives
50mV x 135µS, or 6.75µA, across R
sient gain. Since the current-sense transresistance is
0.3V/A, the value of R
step swing:
In a step-up DC-to-DC converter, if L
put current relates to inductor current by:
Thus, for a 400mA output load step with V
V
Note that the inductor does not limit the response in this
case since it can ramp at 2V/3.3µH, or 606mA/µs. The
output filter capacitor is then chosen so that the C
R
For example:
Since a reasonable value for C
37.5, choose 47µF and rescale RC:
which provides a slightly higher transient gain and con-
sequently less transient droop than previously selected.
If the output filter capacitor has significant ESR, a zero
occurs at:
If Z
with ceramic output capacitors. If Z
it should be cancelled with a pole set by capacitor C
connected from COMPSU to GND:
If C
OUT
LOAD
I
ESR
P
IND(PK)
C
R
is calculated to be < 10pF, it can be omitted.
C
= 3.35V:
C
pole cancels the R
> f
= (V
= (1.25/3.35)(6.7/0.3) x (135µS/(6.28 x 20kHz)
= [1.25(0.3 x 0.4 x 3.35)/2)]/6.75µA = 37kΩ
C
(2/3.35) = 5.35nF
C
C
= 20kHz. Calculate C
= 1.25 I
R
OUT
, it can be ignored, as is typically the case
FB
C
/V
Z
= 47µF x 6.7/6.8nF = 46.3kΩ
R
ESR
OUT
= 37kΩ x 6.8nF/6.7 = 37.5µF
C
C
C
______________________________________________________________________________________
OUT
= 0.3 I
OUT
P
)(R
= 1/(2π C
= C
C
/(1 - D) = 1.25 I
R
LOAD
LOAD
OUT
IND(PK)/
that allows the required load
C
C
C
Small, High-Efficiency, Five-Channel
/R
R
C
OUT
such that transient droop
= R
ESR
CS
OUT
zero:
C
6.75µA
:
)(gm/2π f
Digital Still Camera Power Supply
C
/R
R
C
ESR
ESR
is 47µF rather than
C
IDEAL
C
C
OUT
to provide tran-
)
is less than f
C
V
is used, out-
IN
)(1 - D)
OUT
= 2V and
/V
IN
OUT
C
P
,
The external components required for the step-down
are an inductor, input and output filter capacitors, and
compensation RC network. The MAX1565 step-down
converter provides best efficiency with continuous
inductor current. A reasonable inductor value (LIDEAL)
can be derived from:
which sets the peak-to-peak inductor current at 1/2 the
DC inductor current. D is the duty cycle:
Given L
tion is 0.5 I
1.25 I
be used to reduce inductor size. However, if much
smaller values are used, inductor current rises and a
larger output capacitance may be required to suppress
output ripple.
Larger values than L
output current, but with typically larger inductor size.
The relevant characteristics for step-down compensa-
tion are:
1) Transconductance (from FBSD to COMPSD), gm
2) Step-down slope compensation pole, P
3) Current-sense amplifier transresistance, R
4) Feedback regulation voltage, V
5) Step-down output voltage, V
6) Output load equivalent resistance, R
The key steps for step-down compensation are:
1) Set the compensation RC zero to cancel the R
2) Set the loop crossover below the lower of 1/5 the
If we assume V
350mA, then R
(135µS)
V
(0.6V/A)
in Ω = V
C
slope compensation pole, or 1/5 the switching fre-
quency.
IN
OUT
OUT
/ (πL)
IDEAL
L
. Inductance values smaller than L
IDEAL
pole.
OUT
OUTSD
Step-Down Component Selection
, the peak-to-peak inductor current varia-
LOAD
. The absolute peak inductor current is
IN
= 2 (V
/I
= 3.35V, V
LOAD
IDEAL
= 4.3Ω.
D = V
IN
) D (1 - D)/(I
OUT
can be used to obtain higher
Step-Down Compensation
OUT
/V
SD
IN
Step-Down Inductor
, in V
FB
= 1.5V, and I
OUT
(1.25V)
f
OSC
IDEAL
)
SLOPE
LOAD
OUT
LOAD
can
CS
EA
19
=
=
,
,