MAX1565ETJ+T Maxim Integrated Products, MAX1565ETJ+T Datasheet - Page 22

• 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

The MAX1565’s internal switch step-up and step-down
can be cascaded to make a high-efficiency buck-boost
converter, but it may sometimes be desirable to build a
second buck-boost converter with an AUX_ controller.
One type of step-up/step-down converter is the SEPIC
(Figure 7). Inductors L1 and L2 can be separate induc-
tors or wound on a single core and coupled like a
transformer. Typically, a coupled inductor improves
efficiency since some power is transferred through the
coupling, causing less power to pass through the cou-
pling capacitor (C2). Likewise, C2 should have low ESR
to improve efficiency. The ripple current rating must be
greater than the larger of the input and output currents.
The MOSFET (Q1) drain-to-source voltage rating, and
the rectifier (D1) reverse-voltage rating must exceed
the sum of the input and output voltages. Other types of
step-up/step-down circuits are a flyback converter and
a step-up converter followed by a linear regulator.
Some applications require multiple voltages from a single
converter channel. This is often the case when generating
voltages for CCD bias or LCD power. Figure 8 shows a
two-output flyback configuration with AUX_. The
controller drives an external MOSFET that switches the
transformer primary. Two transformer secondaries
generate the output voltages. Only one positive output
voltage can be fed back, so the other voltages are set
by the turns ratio of the transformer secondaries. The
load stability of the other secondary voltages depends
on transformer leakage inductance and winding resis-
tance. Voltage regulation is best when the load on the
Small, High-Efficiency, Five-Channel
Digital Still Camera Power Supply
Figure 6. AUX_ Channel Powering a White LED Step-Up
Current Source
22
______________________________________________________________________________________
TO V
62Ω
(FOR 20mA)
WHITE
LEDs
Multiple Output Flyback Circuits
1µF
BATT
1µF
10µH
SEPIC Buck-Boost
DL_
FB_
(PARTIAL)
MAX1565
OUTSU
AUX_
PWM
secondary that is not fed back is small when compared
to the load on the one that is. Regulation also improves
if the load current range is limited. Consult the trans-
former manufacturer for the proper design for a given
application.
Negative output voltages can be produced without a
transformer, using a charge-pump circuit with an auxil-
iary controller as shown in Figure 9. When MOSFET Q1
turns off, the voltage at its drain rises to supply current
to V
V
Figure 7. Auxiliary SEPIC Configuration
Figure 8. +15V and -7.5V CCD Bias with Transformer
OUT
Boost with Charge Pump for Positive and
OUT
+ through D1.
AUX_
PWM
+. At the same time, C1 charges to the voltage
(PARTIAL)
MAX1565
1-CELL
MAIN
INPUT
MAX1565
IN
PART OF
OUTSU
TO V
Li+
BATT
DCON
DL_
FB_
1µF
DL
FB
L
1
*LOAD RESISTOR REQUIRED IF -7.5V
OPERATES WITH NO LOAD
Q
1
C
2
L
2
Negative Outputs
D
1
1µF
1µF
R
R
1
2
OUTPUT
3.3V
1.1MΩ
100kΩ
*(SEE NOTE)
+15V
30mA
CCD+
-7.5V
20mA
CCD-