MAX1846EUB+ Maxim Integrated Products, MAX1846EUB+ Datasheet - Page 16

• Manufacturer Part Number: MAX1846EUB+
• Description: IC CNTRLR PWM HI EFF 10-UMAX
• Manufacturer: Maxim Integrated Products
• Type: Inverting, Flybackr

Specifications of MAX1846EUB+

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: -0.5 ~ -200 V
• Current - Output: 5A
• Frequency - Switching: 100kHz ~ 500kHz
• Voltage - Input: 3 ~ 16.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Power - Output: 444mW
• Duty Cycle (max): 97 %
• Output Voltage: 1.25 V
• Mounting Style: SMD/SMT
• Switching Frequency: 500 KHz
• Operating Supply Voltage: 3 V to 16.5 V
• Supply Current: 0.75 mA
• Maximum Operating Temperature: + 85 C
• Fall Time: 200 ns
• Minimum Operating Temperature: - 40 C
• Output Power: 444 mW
• Rise Time: 200 ns
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

High-Efficiency, Current-Mode,
Inverting PWM Controller
Select the next smaller standard value of resistor and
then calculate the compensation capacitor required to
cancel out the output-capacitor-induced pole (P
determined previously.
Choose the next larger standard value of capacitor.
In order for p
loop gain must reach unity at a lower frequency than
the right-half-plane zero or the second output pole,
whichever is lower in frequency. If the second output
pole and the right-half-plane zero are close together in
frequency, the higher resulting phase shift at unity gain
may require a lower crossover frequency. For duty
cycles greater than 50%, slope compensation reduces
A
f
COMP with a capacitor (C
adding extra phase margin at the crossover, the
capacitor (C
the crossover frequency. The value for C
found using:
It might require a couple iterations to obtain a suitable
combination of compensation components.
Finally, the zero introduced by the output capacitor’s
ESR must be compensated. This compensation is
accomplished by placing a capacitor between REF
and FB creating a pole directly in the feedback loop.
Calculate the value of this capacitor using the frequen-
cy of z
with the formula:
When using low-ESR, ceramic chip capacitors (MLCCs)
at the output, calculate the value of C
16
CROS
C
DC
COMP
, reducing the actual crossover frequency from
______________________________________________________________________________________
. It is also a good practice to reduce noise on
ESR
C
2
COMP
C
C
FB
=
and the selected feedback resistor values
COMP2
FB
COMP
5
=
=
=
x
R
2
ESR
6 28
6 28
) should roll-off noise at five times
to compensate the loop, the open-
×
.
.
3 14
.
x C
x P
x f
R
COMP2
O
OUT
×
R
CROS
OUT
1
f
+
OSC
+
1
1
x
R
R
) to ground. To avoid
COMP
2
x R
R
R x R
x R
×
1
1
FB
R
+
COMP
O
1
R
as follows:
×
COMP2
2
x R
2
R
2
COMP
can be
OUT1
)
The maximum output power that the MAX1846/MAX1847
can provide depends on the maximum input power
available and the circuit’s efficiency:
Furthermore, the efficiency and input power are both
functions of component selection. Efficiency losses can
be divided into three categories: 1) resistive losses
across the inductor, MOSFET on-resistance, current-
sense resistor, rectification diode, and the ESR of the
input and output capacitors; 2) switching losses due to
the MOSFET’s transition region, and charging the MOS-
FET’s gate capacitance; and 3) inductor core losses.
Typically, 80% efficiency can be assumed for initial cal-
culations. The required input power depends on the
inductor current limit, input voltage, output voltage, out-
put current, inductor value, and the switching frequen-
cy. The maximum output power is approximated by the
following formula:
where I
inductor current-ripple ratio and is calculated by:
Again, remember that V
MAX1847 is negative.
The MAX1846/MAX1847’s high-switching frequency
demands a high-speed rectifier. Schottky diodes are
recommended for most applications because of their fast
recovery time and low forward voltage. Ensure that the
diode’s average current rating exceeds the peak inductor
current by using the diode manufacturer’s data.
Additionally, the diode’s reverse breakdown voltage must
exceed the potential difference between V
input voltage plus the leakage-inductance spikes. For
high output voltages (-50V or more), Schottky diodes may
not be practical because of this voltage requirement. In
these cases, use an ultrafast recovery diode with ade-
quate reverse-breakdown voltage.
The input capacitor (C
into the inverter. This capacitor is selected the same way
[1 - (LIR / 2)] x [(-V
P
MAX
LIM
P
= [V
OUT(MAX)
is the peak current limit and LIR is the
IN
Applications Information
- (V
LIR = I
LIM
- V
= Efficiency
IN
OUT
OUT
) must provide the peak current
Maximum Output Power
+ I
LPP
+ V
LIM
Input Filter Capacitor
+ V
OUT
/ I
D
x R
) / (V
D
LDC
)]

DS(ON)
for the MAX1846/
Diode Selection
P
IN
IN(MAX)
- V
)] x I
SW
OUT
- V
LIM
and the
LIM
x