MAX1565ETJ-T Maxim Integrated Products, MAX1565ETJ-T Datasheet - Page 15

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

Note that the step-up output supplies both the step-up
load and the step-down input current when the step-
down is powered from the step-up. The step-down
input current reduces the available step-up output cur-
rent for other loads.
The step-down converter can also be operated directly
from the battery as long as the voltage at INSD does
not exceed OUTSU by more than a Schottky diode for-
ward voltage. When using this connection, connect a
Schottky diode from the battery input to OUTSU. There
is also an internal 10kΩ resistance from OUTSU to
INSD, which adds a small additional current drain (of
approximately (V
when INSD is not connected directly to OUTSU.
Step-down direct battery operation improves efficiency
for the step-down output (up to 95%), but limits the
upper limit of the output voltage to 200mV less than the
minimum battery voltage. In 1-cell Li+ designs (with a
2.7V min), the output can be set up to 2.5V. In 2-cell
alkaline or NiMH designs, the output may be limited to
1.5V or 1.8V, depending on the minimum allowed cell
voltage.
The step-down can only be briefly operated in dropout
since the MAX1565 fault protection detects the out-of-
regulation condition and activates after 100,000 OSC
cycles, or 200ms at 500kHz. At that point, all MAX1565
channels shut down.
Figure 3. PWM Auxiliary Controller Functional Diagram
COMP
OSC
REF
FB
*SOFT-START RAMPS REFI FROM 0V TO V
Direct Battery Step-Down Operation
OUTSU
______________________________________________________________________________________
0.85 REF
- V
Small, High-Efficiency, Five-Channel
INSD
REFI
)/10kΩ from OUTSU
Digital Still Camera Power Supply
REF
IN 4096 CLOCK CYCLES.
START*
LEVEL
SHIFT
SOFT-
CLK
The three auxiliary controllers operate as fixed-frequency
voltage-mode PWM controllers. They do not have
internal MOSFETs, so output power is determined by
external components. The controllers regulate output
voltage by modulating the pulse width of the DL_ drive
signal to an external N-channel MOSFET switch.
Figure 3 shows a functional diagram of an AUX
controller channel. A sawtooth oscillator signal at OSC
governs timing. At the start of each cycle, DL_ goes
high, turning on the external N-FET switch. The switch
then turns off when the internally level-shifted sawtooth
rises above COMP_ or when the maximum duty cycle is
exceeded. The switch remains off until the start of the
next cycle. A transconductance error amplifier forms an
integrator at COMP_ so that DC high-loop gain and
accuracy can be maintained.
The auxiliary controllers do not start until the step-up
DC-to-DC output is in regulation. If the step-up, step-
down, or any of the auxiliary controllers remains faulted
for 100,000 OSC cycles, then all MAX1565 channels
latch off.
PROTECTION
FAULT
R
S
Auxiliary DC-to-DC Controllers
ENABLE
Q
DL_
15