Max5069 – Rainbow Electronics MAX5069 User Manual
Page 10
MAX5069
Undervoltage Lockout
The MAX5069 features an input voltage UVLO/EN func-
tion to enable the PWM controller before any operation
can begin. The MAX5069A/D shut down if the voltage
at UVLO/EN falls below its 1.18V threshold. The
MAX5069B/C also incorporate a UVLO hysteresis input
to set the desired turn-off voltage.
MAX5069A/D UVLO Adjustment
The MAX5069A/D have an input voltage UVLO/EN with
a 1.231V threshold. Before any operation can com-
mence, the UVLO/EN voltage must exceed the 1.231V
threshold. The UVLO circuit keeps the PWM compara-
tor, ILIM comparator, oscillator, and output drivers shut-
down to reduce current consumption (see the
Functional Diagram).
Calculate R6 in Figure 2 by using the following formula:
where V
ULR2
is the UVLO/EN’s 1.231V rising threshold
and V
ON
is the desired startup voltage. Choose an R7
value in the 20kΩ range.
After a successful startup, the MAX5069A/D shut down
if the voltage at UVLO/EN drops below its 1.18V fall-
ing threshold.
MAX5069B/C UVLO with
Programmable Hysteresis
In addition to programmable undervoltage lockout dur-
ing startup, the MAX5069B/C incorporate a UVLO/EN
R
V
V
R
ON
ULR
6
1
7
2
=
×
−
High-Frequency, Current-Mode PWM Controller
with Accurate Oscillator and Dual FET Drivers
10
______________________________________________________________________________________
MAX5069B
IN
NDRVA
NDRVB
HYST
UVLO/EN
CS
COMP
V
CC
AGND PGND
REG5
RT
FB
DT
FLTINT
R1
C1
Q1
Q2
V
IN
C2
C3
C4
R3
R4
R9
R2
R8
V
OUT
SCOMP
C5
C7
D1
D3
D2
R5
C6
R10
R6
R
HYST
R7
Figure 1. Nonisolated Power Supply with Programmable Input Supply Voltage