MAX15001 Maxim Integrated Products, MAX15001 Datasheet - Page 11

• Manufacturer Part Number: MAX15001
• Description: (MAX15000 / MAX15001) Current-Mode PWM Controllers
• Manufacturer: Maxim Integrated Products

The NDRV output drives an external n-channel MOSFET.
The internal regulator output (V
9V, drives NDRV. For the universal input voltage range,
the MOSFET used must withstand the DC level of the
high-line input voltage plus the reflected voltage at the
primary of the transformer. Most applications that use the
discontinuous flyback topology require a MOSFET rated
at 600V. NDRV can source/sink in excess of 650/1000mA
peak current; therefore, select a MOSFET that will yield
acceptable conduction and switching losses.
Use an external resistor at RT to program the
MAX15000/MAX15001 internal oscillator frequency
between 50kHz and 2.5MHz. The MAX15000A/
MAX15001A output switching frequency is one-half of
the programmed oscillator frequency with a 50% duty
cycle. The MAX15000B/MAX15001B output switching
frequency is one-quarter of the programmed oscillator
frequency with a 75% duty cycle.
The MAX15000A/MAX15001A and MAX15000B/
MAX15001B have programmable output switching fre-
quencies from 25kHz to 625kHz and 12.5kHz to
625kHz, respectively. Use the following formulas to
determine the appropriate value of the resistor R12
(see Figure 1) needed to generate the desired output
switching frequency (f
where R12 is the resistor connected from RT to GND
(see Figure 1).
Connect an RC network in parallel with R12 as shown in
Figure 1. The RC network should consist of a 100nF
capacitor C6 (for stability) in series with resistor R15
which serves to further minimize jitter. Use the following
formula to determine the value of R15:
For example, if R12 is 4k , R15 becomes 707 .
R
R
12
12
10
2
10
4
f
n-Channel MOSFET Switch Driver
f
SW
SW
10
10
Oscillator/Switching Frequency
R
15
for the MAX
for the MAX
______________________________________________________________________________________
SW
88 9
) at the NDRV output:
.
Programmable Switching Frequency
Current-Mode PWM Controllers with
15000
15000
CC
R
), set to approximately
12
B MAX
A MAX
1
4
/
/
15001
15001
B
A
.
.
The MAX15000/MAX15001 include an internal error
amplifier to regulate the output voltage in the case of a
nonisolated power supply (see Figure 1). For the circuit
in Figure 1, calculate the output voltage using the fol-
lowing equation:
where V
is internally connected to a digital soft-start circuit that
gradually increases the reference voltage during start-
up applied to this input. This forces the output voltage
to come up in an orderly and well-defined manner
under all load conditions.
The error amplifier may also be used to regulate the ter-
tiary winding output which implements a primary-side-
regulated, isolated power supply (see Figure 6). For the
circuit in Figure 6, calculate the output voltage using
the following equation:
where N
is the number of tertiary winding turns, and both V
and V
Figure 4. Primary-Side Output Voltage Soft-Start During Initial
Startup for the Circuit in Figure 6
D2
REF
S
V
are the diode drops at the respective outputs.
OUT
is the number of secondary winding turns, N
= 1.23V. The amplifier’s noninverting input
V
N
N
OUT
S
T
1
1
R
R
2ms/div
Internal Error Amplifier
1
2
R
R
100mA LOAD ON/V
100mA LOAD ON/V
14
13
V
REF
V
REF
V
MAX15000 fig04
D
6
OUT1
OUT2
V
V
2V/div
D
OUT
2
11
D6
T