MAX17500AEVKIT Maxim Integrated Products, MAX17500AEVKIT Datasheet - Page 4

• Manufacturer Part Number: MAX17500AEVKIT
• Description: Power Management Modules & Development Tools
• Manufacturer: Maxim Integrated Products

windings provide Q5% regulation for the +5V output set
point. Resistors R7 and R12 are adjusted to preload
the tertiary winding for the desired +5V output set point
and regulation. UVLO provides controlled turn-on and
shutdown during brownouts, power-up, or power-down.
The UVLO settings can be changed by replacing
resistor R3. Startup resistor R6 and reservoir capacitor
C16 enable the device to start up within approximately
37ms. The digital soft-start allows the output voltage to
slowly ramp up in a controlled manner within 6ms.
The device controller switches at a fixed 350kHz
frequency and is set by resistor-capacitor networks R14,
R15/C18, and C19. The switching duty cycle is varied
to control energy transfer to the isolated outputs. The
maximum duty cycle is 50% for the EV kit’s discontinuous
current-mode flyback design.
The EV kit features two methods to shut down the
flyback DC-DC converter. Jumper JU1 can be used to
shut down the flyback DC-DC converter. An alternate
method, remote-control shutdown, can be done with a
user-supplied open-collector/drain transistor or relay
contact connected to the SHDN and -VIN PCB pads on
the EV kit. Table 1 lists the shutdown mode.
The EV kit’s outputs (V
to +5V and +15V, respectively, by the T1 transformer
tertiary windings, the transformer’s respective secondary
output windings, and the resistor-divider R1 and R2. To
generate scaled output voltages other than +5V (+4.2V
to +6.8V) and +15V (+12.3V to +20.2V), select different
voltage-divider resistors (R1, R2). Resistor R2 is typically
chosen to be less than 5kI. When evaluating other
output voltages, verify that the secondary outputs’
components affected by increased voltage are rated
for the appropriate voltage. Components C3, C4, C13,
and D4 of V
should have their respective voltage rating evaluated.
Using the desired scaled output voltages, resistor R1 is
then found by the following equation:
Table 1. Jumper JU1 Shutdown Mode
Current Limits, and Undervoltage Lockouts
R1 = [[{(V
SHUNT POSITION
Not installed
Installed
OUT1
OUT1
- V
_________________________________________________________________ Maxim Integrated Products 4
Shutdown Mode (Jumper and
and components C5, C15, and D5
V
VD1
OUT1
Evaluating Other Voltages,
) x N
Remote-Control Methods)
OUT1
and V
T
/N
1
} - V
OUT2
UVLO resistors R3 and R4 determine startup voltage
and V
VD6
Output Voltages
OUT2
]/V
FB
) are set
DEVICE UVLO/EN PIN
-1] x R2
Pulled low to -VIN
where:
Both output voltages are scaled up or down since the
respective transformer’s secondary output turns set the
actual voltage. Additionally, the maximum current for
each output should be limited to less than 1.5A for V
and 100mA for V
The EV kit features current limiting for the transformer’s
primary current. The device turns off switching MOSFET
N1 when the voltage at the device’s CS pin reaches +1V.
Current-sense resistor R5 (0.6I) limits the transformer
peak primary current to 1.67A (+1V/0.6I = 1.67A). This
limits the average short-circuit current on the secondary
outputs typically to 1.42A (average with I
and 0.52A (average with I
V
current-sense resistor R5 must be replaced with a different
surface-mount resistor (1206 size), as determined by the
following equation.
When considering the transformer’s primary input
current:
where V
maximum primary current.
The EV kit features an accurate UVLO circuit that
prevents operation below the programmed input-supply
start voltage. Resistors R3 and R4 set the voltage at
the device’s UVLO/EN pin, which determines the UVLO
wake-up and shutdown levels of +1.23V (typ) and +1.17V
(typ), respectively. To evaluate other wake-up and shut-
down levels, replace R3 with another surface-mount
OUT2
V
N
N
output turns.
V
V
diode D6 forward-voltage drop.
V
Schottky diode D1 forward-voltage drop at 1.5A.
Evaluates: MAX17500A
OUT1
FB
VD6
VD1
T
1
= 15 is the transformer’s tertiary turns.
= 6 is the transformer’s secondary V
= +1.23V is the device reference voltage.
, respectively. To evaluate a lower current limit,
= +1V is the circuit’s tertiary winding, high-speed
= +0.45V (typ) is the circuit’s secondary-side
SENSE
is the +5V output.
= +1V and I
R5 = (V
OUT2
.
SENSE
Undervoltage Lockout (UVLO)
OUT1
PRIMARY
/I
PRIMARY
DEVICE OUTPUT
Shutdown mode
= 1.5A) for V
Device enabled
is the transformer’s
Current Limiting
)
OUT2
OUT1
= 100mA)
OUT1
, +5V
OUT1
and