MAX1585ETJ+ Maxim Integrated Products, MAX1585ETJ+ Datasheet - Page 18

• Manufacturer Part Number: MAX1585ETJ+
• Description: IC DGTL CAM PWR SUP 5CH 32TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1585ETJ+

• Applications: Controller, Digital Camera
• Voltage - Input: 0.7 ~ 5.5 V
• Number Of Outputs: 5
• Voltage - Output: 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

end of the soft-start interval. If PVSU is dragged below
the input, the overload is supplied by the body diode of
the internal synchronous rectifier or by a Schottky diode
connected from the battery to PVSU. If desired, this
overload current can be interrupted by a P-channel
MOSFET controlled by SCF, as shown in Figure 15.
The MAX1584/MAX1585 have internal 1.250V refer-
ences. Connect a 0.1µF ceramic bypass capacitor from
REF to GND within 0.2in (5mm) of the REF pin. REF can
source up to 200µA and is enabled when ONSU is high
and PVSU is above 2.5V. The auxiliary controllers and
MAX1801 slave controllers (if connected) each sink up
to 30µA REF current during startup. If the application
requires that REF be loaded beyond 200µA, buffer REF
with a unity-gain amplifier or op amp.
All MAX1584/MAX1585 DC-DC converter channels
employ fixed-frequency PWM operation. The operating
frequency is set by an RC network at the OSC pin. The
range of usable settings is 100kHz to 1MHz. When
MAX1801 slave controllers are added, they operate at
the frequency set by OSC.
The oscillator uses a comparator, a 150ns one-shot,
and an internal NFET switch in conjunction with an
external timing resistor and capacitor (Figure 4). When
the switch is open, the capacitor voltage exponentially
approaches the step-up output voltage from zero with a
time constant given by the product of R
The comparator output switches high when the capaci-
tor voltage reaches V
5-Channel Slim DSC Power Supplies
Figure 4. Oscillator Functional Diagram
18
______________________________________________________________________________________
OSC
V
SU
R
C
OSC
OSC
REF
(1.25V)
V
(1.25V). In turn, the one-shot
REF
ONE-SHOT
150ns
MAX1584
MAX1585
OSC
Reference
Oscillator
and C
OSC
.
activates the internal MOSFET switch to discharge the
capacitor within a 150ns interval, and the cycle
repeats. The oscillation frequency changes as the main
output voltage ramps upward following startup. The
oscillation frequency is then constant once the main
output is in regulation.
The MAX1584/MAX1585 internal control and reference-
voltage circuitry receive power from PVSU and do not
function when PVSU is less than 2.5V. To ensure low-
voltage startup, the step-up employs a low-voltage
startup oscillator that activates at 0.9V if a Schottky rec-
tifier is connected from V
Schottky rectifier). The startup oscillator drives the inter-
nal N-channel MOSFET at LXSU until PVSU reaches
2.5V, at which point voltage control is passed to the
current-mode PWM circuitry.
Once in regulation, the MAX1584/MAX1585 operate
with inputs as low as 0.7V since internal power for the
IC is supplied by PVSU. At low input voltages, the step-
up can have difficulty starting into heavy loads (see the
Minimum Startup Voltage vs. Load Current graph in the
Typical Operating Characteristics section); however,
this can be remedied by connecting an external P-
channel load switch driven by SCF so the load is not
connected until the PVSU is in regulation (Figure 15).
The step-up converter activates with a high input at
ONSU. The step-down and auxiliary DC-DC converters
1, 2, and 3 activate with a high input at ONSD, ON1,
ON2, and ON3, respectively. The step-down and auxil-
Figure 5. +15V LCD Bias with Basic Boost Topology
NOTE: THIS CIRCUIT CAN OPERATE WITH AUX1 OR
AUX2 ON THE MAX1584, AND WITH AUX1 ON THE MAX1585
(PARTIAL)
MAX1584
MAX1585
PWM
AUX
Low-Voltage Startup Oscillator
PVSU
FB_
DL_
BATT
Q1
V
TO
BATT
ON_ Control Inputs
to PVSU (1.1V with no
D6
+15V
50mA
LCD