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MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

Skip Mode/Standby Mode

device enters skip mode operation. Skip mode turns off

the majority of circuitry and allows the output to drop

below regulation voltage before the switch is turned on

again. The lower the load current, the longer it takes for

the regulator to initiate a new cycle. Because the con-

verter skips unnecessary cycles and turns off the majority

of circuitry, the converter efficiency increases. When the

high-side FET stops switching for more than 50Fs, most

of the internal circuitry, including LDO, draws power from

from the battery to drop to only 30FA.

Overtemperature Protection

Thermal-overload protection limits the total power dis-

sipation in the device. When the junction temperature

exceeds +175NC (typ), an internal thermal sensor

shuts down the internal bias regulator and the step-

down converter, allowing the IC to cool. The thermal

sensor turns on the IC again after the junction tempera-

ture cools by 15NC.

Applications Information

Setting the Output Voltage

Connect FB to BIAS for a fixed 5V output voltage. To set

the output to other voltages between 1V and 10V, con-

nect a resistive divider from output (OUT) to FB to GND

following equation:

OUT

FB1

FB2

FB

V

R

R

1

V









=

−





















Internal Oscillator

connected from FOSC to GND. See Figure 2 to select the

For example, a 400kHz switching frequency is set with

lower inductor values and less output capacitance.

at higher switching frequencies, but core losses, gate

charge currents, and switching losses increase.

Inductor Selection

Three key inductor parameters must be specified for

operation with the device: inductance value (L), inductor

select inductance value, the ratio of inductor peak-to-

peak AC current to DC average current (LIR) must be

selected first. A good compromise between size and loss

is a 30% peak-to-peak ripple current to average-current

ratio (LIR = 0.3). The switching frequency, input voltage,

output voltage, and selected LIR then determine the

inductor value as follows:

OUT SUP

OUT

SUP SW OUT

V

(V

V

)

L

V

f

I

LIR

−

=

efficiency is optimum for typical conditions). The switch-

section). The exact inductor value is not critical and can

be adjusted to make trade-offs among size, cost, efficien-

cy, and transient response requirements. Table 1 shows

a comparison between small and large inductor sizes.

Figure 1. Adjustable Output-Voltage Setting

FB

MAX16909

100

90

70 80

40 50 60

30

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0

20

110