MAX5094DAUA+ Maxim Integrated Products, MAX5094DAUA+ Datasheet - Page 14

• Manufacturer Part Number: MAX5094DAUA+
• Description: IC CNTRLR PWM CURRENT MD 8-UMAX
• Manufacturer: Maxim Integrated Products

Specifications of MAX5094DAUA+

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 1MHz
• Duty Cycle: 50%
• Voltage - Supply: 8 V ~ 25 V
• Buck: No
• Boost: No
• Flyback: Yes
• Inverting: No
• Doubler: No
• Divider: Yes
• Cuk: No
• Isolated: Yes
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Frequency-max: 1MHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

To calculate the capacitance required, use the following
formula:
where:
I
ply current after startup (see the Typical Operating
Characteristics to find the I
total gate charge for the MOSFET, f
switching frequency, V
teresis (0.8V), and t
by external circuitry.
Size the resistor R
time period, t
ing equations to calculate the average charging current
(I
Where V
the application (36V for telecom), V
UVLO wake-up level (8.4V), and I
current at startup (65µA, max). Choose a higher value for
R
can be tolerated to minimize power loss in R
The equation for C
of C
C
The above startup method is applicable to circuits where
the tertiary winding has the same phase as the output
windings. Thus, the voltage on the tertiary winding at any
given time is proportional to the output voltage and goes
through the same soft-start period as the output voltage.
High-Performance, Single-Ended, Current-Mode
PWM Controllers
14
CC
CST
ST
ST
is the MAX5094/MAX5095s’ maximum internal sup-
than the one calculated above if longer startup times
ST
using:
______________________________________________________________________________________
) and the startup resistor (R
, yet neglects the current through R
INMIN
C
ST
ST
R
is the minimum input supply voltage for
, for the calculated C
I
ST
I
C
CST
CC
ST
ST
ST
SS
above gives a good approximation
I
I
V
G
according to the desired startup
G
HYST
is the soft-start time, which is set
V
INMIN
I
I
CST
CC
SUVR
= Q
V
HYST
V
IN
V
t
HYST
INMIN
G
is the bootstrap UVLO hys-
ST
I
G
at a given f
I
START
f
R
V
SW
C
SUVR
ST
ST
t
START
SS
ST
2
):
SUVR
8
SW
ST
V
. Use the follow-
is the V
is the converter
OSC
is the bootstrap
(
t
SS
ST
ST
). Q
. Fine tune
)
.
IN
G
supply
is the
The minimum discharge time of C
must be greater than the soft-start time (t
The minimum turn-on supply voltage for the
MAX5094/MAX5095 is 8.4V. Once V
the reference powers up. There is 0.8V of hysteresis
from the minimum turn-on voltage to the UVLO thresh-
old. Once V
operates with V
7.6V the device is in UVLO. When in UVLO, the quies-
cent supply current into V
and OUT and REF are pulled low.
OUT drives an external n-channel MOSFET and swings
from GND to V
absolute maximum V
OUT is a push-pull output with the on-resistance of the
PMOS typically 3.5 and the on-resistance of the NMOS
typically 4.5 . The driver can source 2A typically and
sink 1A typically. This allows for the MAX5094/MAX5095
to quickly turn on and off high gate-charge MOSFETs.
Bypass V
to GND, placed close to the MAX5094/MAX5095. The
average current sourced to drive the external MOSFET
depends on the total gate charge (Q
frequency of the converter. The power dissipation in the
MAX5094/MAX5095 is a function of the average output-
drive current (I
culate the power dissipation in the device due to I
where, I
Typical Operating Characteristics for the operating
supply current at a given frequency.
The MAX5094 includes an internal error amplifier. The
inverting input is at FB and the noninverting input is inter-
nally connected to a 2.5V reference. The internal error
amplifier is useful for nonisolated converter design (see
Figure 6) and isolated design with primary-side regulation
through a bias winding (see Figure 5). In the case of a
nonisolated power supply, the output voltage is:
where, R1 and R2 are from Figure 6.
CC
CC
CC
is the operating supply current. See the
with one or more 0.1µF ceramic capacitors
DRIVE
PD = (I
CC
V
CC
reaches 8.4V, the MAX5094/MAX5095
OUT
Undervoltage Lockout (UVLO)
. Ensure that V
I
down to 7.6V. Once V
DRIVE
). Use the following equation to cal-
GS
DRIVE
Error Amplifier (MAX5094)
1
rating of the external MOSFET.
= Q
CC
R
R
+ I
1
2
G
falls back to 32µA (typ),
CC
x f
2 5 .
CC
) x V
SW
ST
MOSFET Driver
V
remains below the
CC
from 8.4V to 7.6V
G
CC
SS
) and operating
CC
).
reaches 8.4V,
goes below
DRIVE
: