MAX6497ATA+T Maxim Integrated Products, MAX6497ATA+T Datasheet - Page 8

• Manufacturer Part Number: MAX6497ATA+T
• Description: IC CNTRLR PROT SW 8-TDFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX6497ATA+T

• Voltage - Working: 72V
• Technology: Mixed Technology
• Power (watts): 1.45W
• Number Of Circuits: 1
• Applications: General Purpose
• Package / Case: 8-TDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Clamping: -

72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
The gate cycles during overvoltage-limit and overvolt-
age-switch modes are quite similar but have distinct
characteristics. In overvoltage-switch mode, GATE is
enhanced to (V
age remains below the overvoltage fault threshold
(OVSET < V
(OVSET ≥ V
OUTFB, turning off the external MOSFET and discon-
necting the load from the input. GATE remains low
(MOSFET off) as long as the V
overvoltage fault threshold. As V
overvoltage fault threshold, GATE is again enhanced to
(V
In overvoltage-limit mode, GATE is enhanced to (V
+10V) while the monitored OUTFB voltage remains
below the overvoltage fault threshold (OVSET < V
When an overvoltage fault occurs (OVSET ≥ V
GATE is pulled one diode drop below OUTFB until
OUTFB drops 5% below the overvoltage fault threshold
(MAX6495/MAX6496/MAX6499). GATE is then turned
back on until OUTFB reaches the overvoltage fault
threshold and GATE is again turned off. GATE cycles in
a sawtooth waveform until OUTFB remains below the
overvoltage fault threshold and GATE remains con-
stantly on (V
tooth GATE output operates the MOSFET in a
switched-linear mode while the input voltage remains
above the overvoltage fault threshold. The sawtooth fre-
quency depends on the load capacitance, load current,
and MOSFET turn-on time (GATE charge current and
GATE capacitance).
GATE goes high when the following startup conditions
are met: V
high, an overvoltage fault is not present, and the device
is not in thermal shutdown.
The MAX6499 includes undervoltage and overvoltage
comparators for window detection (see Figures 3 and
12). GATE is enhanced and the n-channel MOSFET is
on when the monitored voltage is within the selected
“window.” When the monitored voltage falls below the
lower limit (V
(V
ing off the MOSFET. The application in Figure 3 shows
the MAX6499 enabling the DC-DC converter when the
monitored voltage is in the selected window.
The resistor values R1, R2, and R3 can be calculated
as follows:
8
IN
TRIPHIGH
_______________________________________________________________________________________
+ 10V).
Undervoltage Monitoring (MAX6499)
IN
) of the window, GATE falls to OUTFB turn-
TH+
TH+
IN
is above the UVLO threshold, SHDN is
TRIPLOW
), GATE is pulled one diode drop below
IN
+10V). The overvoltage limiter’s saw-
). When an overvoltage fault occurs
+ 10V) while the monitored V
) or exceeds the upper limit
IN
IN
voltage is above the
falls back below the
IN
TH+
TH+
volt-
IN
),
).
where R
Use the following steps to determine the values for R1,
R2, and R3:
1) Choose a value for R
2) Calculate R3 based on R
3) Calculate R2 based on R
4) Calculate R1 based on R
To improve ESD protection, keep R3 ≥ 1kΩ.
Figure 3. MAX6499 Window-Detector Circuit
R3. Because the MAX6499 has very high input
impedance, R
upper trip point:
lower trip point:
V
IN
TOTAL
R1
R2
R3
V
V
TRIPLOW
TRIPHIGH
R
2
R
= R1 + R2 + R3.
3 =
=
R1 = R
TOTAL
⎡
⎢
⎢
⎣
(
V
SHDN
UVSET
OVSET
TH
=
V
=
IN
TH
V
TOTAL
−
(
can be up to 5MΩ.
(
TRIPLOW
V
TOTAL
V
)
V
MAX6499
+
TH
TRIPHIGH
TH
×
GATE
CLEAR
×
TOTAL
−
TOTAL
+
R
)
– R2 – R3
R
)
, the sum of R1, R2, and
TOTAL
TOTAL
⎛
⎜
⎝
TOTAL
⎛
⎜
⎝
OUTFB
R
R
R
GND
2
, R2, and R3:
, R3, and the desired
TOTAL
TOTAL
R
+
3
⎤
⎥
⎥
⎦
and the desired
R
−
3
IN
CONVERTER
⎞
⎟
⎠
⎞
⎟
⎠
R
DC-DC
GND
3
OUT