Datasheet

MAX17598/MAX17599
Low I
Q
, Wide-Input Range, Active Clamp
Current-Mode PWM Controllers
14Maxim Integrated
Figure 2. Programming EN/UVLO, OVI
Linear Regulator (V
DRV
)
The MAX17598/MAX17599 have an internal linear regu-
lator that is powered from the V
IN
pin. The output of
the linear regulator is connected to the V
DRV
pin, and
should be decoupled with a 1FF capacitor to ground
for stable operation. The V
DRV
converter output sup-
plies the MOSFET drivers internal to the MAX17598/
MAX17599. The V
DRV
voltage is regulated at 7.4V (typ)
in the MAX17598, and at 4.9V (typ) in the MAX17599. The
maximum operating voltage of the IN pin is 29V for the
MAX17598 and 36V for the MAX17599.
Maximum Duty Cycle (Dmax)
The MAX17598/MAX17599 operate at a maximum duty
cycle of 72.5% (typ). When the SLOPE pin is left OPEN,
the ICs have the necessary amount of slope compensa-
tion to provide stable, jitter-free current-mode control
operation in applications where the operating duty cycle
is less than 50%. Slope compensation is necessary for
stable operation of current-mode controlled converters
at duty cycles greater than 50%, in addition to the loop
compensation required for small signal stability. The
MAX17598/MAX17599 implement a SLOPE pin for this
purpose. See the Slope Compensation Programming
section for more details.
Applications Information
Startup Voltage and Input Overvoltage
Protection Setting (EN/UVLO, OVI)
The EN/UVLO pin in the MAX17598/MAX17599 serves
as an enable/disable input, as well as an accurate
programmable undervoltage lockout (UVLO) pin. The
MAX17598/MAX17599 do not commence startup opera-
tions unless the EN/UVLO pin voltage exceeds 1.21V
(typ). The MAX17598/MAX17599 turn off if the EN/UVLO
pin voltage falls below 1.15V (typ). A resistor divider from
the input DC bus to ground maybe used to divide down
and apply a fraction of the input DC voltage to the EN/
UVLO pin as shown in Figure 2. The values of the resistor
divider can be selected so that the EN/UVLO pin voltage
exceeds the 1.21V (typ) turn on threshold at the desired
input DC bus voltage. The same resistor divider can be
modified with an additional resistor, R
OVI
, to implement
input overvoltage protection, in addition to the EN/UVLO
functionality as shown in Figure 2. When the voltage at the
OVI pin exceeds 1.21V (typ), the MAX17598/MAX17599
stop switching. Switching resumes with soft-start opera-
tion, only if the voltage at the OVI pin falls below 1.15V
(typ). The OVI feature is easily disabled by tying the pin
to ground. For given values of startup DC input voltage
(V
START
) and input overvoltage protection voltage (V
OVI
),
the resistor values for the divider can be calculated as
follows, assuming a 24.9kI resistor for R
OVI
. R
SUM
rep-
resents the series combination of several resistors that
might be needed in high-voltage DC bus applications
(MAX17598) or a single resistor in low-voltage DC-DC
applications (MAX17599).
OVI
EN
START
V
R 24.9 1 k ,
V

= × −W


where V
START
and V
OVI
are in volts.
[ ]
START
SUM EN
V
R 24.9 R 1 k ,
1.21

= + × −W


where R
EN
is in kI. R
SUM
might need to be implemented
as equal multiple resistors in series (R
DC1
, R
DC2
, R
DC3
)
so that voltage across each resistor is limited to its maxi-
mum operating voltage.
= = = W
SUM
DC1 DC2 DC3
R
R R R k.
3
MAX1759
8
MAX1759
9
R
DC1
R
DC2
R
DC3
R
SUM
EN/UVLO
OVI
R
EN
R
OVI
V
DC