MAX5069AAUE データシートの表示（PDF） - Maxim Integrated

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MAX5069AAUE

High-Frequency, Current-Mode PWM Controller with Accurate Oscillator and Dual FET Drivers

Maxim Integrated 

High-Frequency, Current-Mode PWM Controller

with Accurate Oscillator and Dual FET Drivers

MAX5069A/D

VIN

R6

UVLO/EN

R7

1.23V

1.18V

VHYST = VON - VOFF

VOFF

VON

Figure 2. Setting the MAX5069A/D Undervoltage Lockout

Threshold

hysteresis that allows the user to set a voltage (VOFF) to

disable the controller (see Figure 3).

At the beginning of the startup sequence, UVLO/EN is

below the 1.23V threshold, and Q1 turns on connecting

RHYST to GND (Figure 4). Once the UVLO 1.23V thresh-

old is crossed, Q1 turns off, resulting in the series com-

bination of R6, RHYST, and R7, placing the MAX5069 in

normal operating condition.

Calculate the turn-on voltage (VON) by using the fol-

lowing formula:

R6

=

⎛

⎝⎜

VON

VULR2

⎞

− 1⎠⎟ ×

RHYST

where VULR2 is the UVLO/EN’s 1.23V rising threshold.

Choose an RHYST value in the 20kΩ range.

The MAX5069 turns off when the MAX5069 UVLO/EN

falls below the 1.18V falling threshold. The turn-off volt-

age (VOFF) is then defined as:

R7

=

R6

/

⎛

⎝⎜

VOFF

VULF2

⎞

− 1⎠⎟ −

RHYST

where VULF2 is the 1.18V UVLO/EN falling threshold.

Bootstrap Undervoltage Lockout

(MAX5069A/B)

In addition to the externally programmable UVLO func-

tion offered by the MAX5069, the MAX5069A/B feature

an additional internal bootstrap UVLO for use in high-

voltage power supplies (see the Functional Diagram).

This allows the device to bootstrap itself during initial

Figure 3. MAX5069 Hysteresis

MAX5069B/C

VIN

R6

UVLO/EN

1.23V

1.18V

HYST

Q1

RHYST

R7

Figure 4. Setting the MAX5069B/C Turn-On/Turn-Off Voltages

power-up. The MAX5069A/B start when VIN exceeds

the bootstrap UVLO threshold of 23.6V.

During startup, the UVLO circuit keeps the PWM com-

parator, ILIM comparator, oscillator, and output drivers

shut down to reduce current consumption. Once VIN

reaches 23.6V, the UVLO circuit turns on both the PWM

and ILIM comparators, as well as the oscillator, and

allows the output driver to switch. If VIN drops below

9.7V, the UVLO circuit shuts down the PWM compara-

tor, ILIM comparator, oscillator, and output drivers,

returning the MAX5069A/B to the startup mode.

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