MAX5068A/B/D/F UVLO with

Programmable Hysteresis

In addition to programmable undervoltage lockout dur-

ing startup, the MAX5068A/B/D/F incorporate a

UVLO/EN hysteresis that allows the user to set a volt-

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

below the 1.23V threshold, Q1 turns on connecting

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

normal operating condition.

lowing formula:

Ω range.

The MAX5068 turns off when the MAX5068 UVLO/EN

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

Bootstrap Undervoltage Lockout

(MAX5068A/C/D Only)

In addition to the externally programmable UVLO func-

tion offered by the MAX5068, the MAX5068A/C/D fea-

ture an additional internal bootstrap UVLO for use in

high-voltage power supplies (see the Functional

Diagram). This allows the device to bootstrap itself dur-

exceeds the bootstrap UVLO threshold of 23.6V.

RR

V

V

R

OFF

ULF

HYST

76

1

2

/

=

⎛

⎝⎜

⎞

⎠⎟

−−

R

V

V

R

ON

ULR

HYST

61

2

=

⎛

⎝⎜

⎞

⎠⎟

×

−

High-Frequency, Current-Mode PWM Controller

with Accurate Programmable Oscillator

______________________________________________________________________________________

11

MAX5068C/E

1.23V

1.18V

UVLO/EN

R7

R6

Figure 2. Setting the MAX5068C/E Undervoltage Lockout

Threshold

Figure 3. MAX5068 Hysteresis

MAX5068A/B/D/F

1.23V

1.18V

UVLO/EN

HYST

R6

R7

Q1

Figure 4. Setting the MAX5068A/B/D/F Turn-On/Turn-Off Voltages