Low-Profile, 5V/12V or Adjustable, Step-Up

DC-DC Converters for Flash Memory/PCMCIA Cards

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9

The on/off times are determined by the input and output

voltages:

K is typically 3µs-V for the MAX606 and 6µs-V for the

MAX607. This factor is chosen to set the optimum

switching frequency and the one-cycle current limit,

which determines the no-load output ripple at low out-

put-to-input voltage differentials. The factor of 0.5 in the

off-time equation is the typical switch off-time ratio. This

ratio guarantees high efficiency under a heavy load by

allowing the inductor to operate in continuous-conduc-

tion mode. For example, a switch off-time ratio of 1

would cause the device to operate on the edge of dis-

continuous-conduction mode.

To determine the actual switch off-time ratio for a par-

then solve for the ratio by substituting these values into

the off-time equation.

Unlike PWM converters, the MAX606/MAX607 generate

variable-frequency switching noise. However, the

amplitude of this noise does not exceed the product of

the switch current limit and the output capacitor equiva-

lent series resistance (ESR). Traditional clocked-PFM or

pulse-skipping converters cannot make this claim.

Output Voltage Selection

The MAX606/MAX607 output voltage is pin-program-

mable to 5V and 12V, and also adjustable to voltages

put, to GND for a 12V output, or to a resistive divider

between the output and GND for an adjustable output.

Always connect OUT to the output.

UNDER-

VOLTAGE

LOCKOUT

DUAL

MODE

REF

CURRENT-LIMIT

COMPARATOR

ERROR

COMPARATOR

TIMING CIRCUIT

CONTROL

LOGIC

EN

ON

INH

OFF

SHDN

FB

INT/EXT

FB

5V/12V

OUT

SS

PGND

INTERNAL

POWER

1

Ω SWITCH

LX

IN

DRIVER

MAX606

MAX607

Figure 3. Functional Diagram