Datasheet
MAX17595 Evaluation Kit
Evaluates: MAX17595 as Flyback Converter
3Maxim Integrated
Quick Start
Required Equipment
• Isolationtransformer
• Variac
• Twovoltmeters
Warnings:
• ExerciseCaution when connecting and measuring
off-line voltages.
• Voltageattheprimarysidecanbeashighas700V
DC.
• Weareyeprotectivegearatalltimes.
• Donottouchanypartofthecircuitwithbarehands
or conductive materials when powering up.
• Makesurethatallhigh-voltage capacitorsarefully
discharged before handling.
VOUT Setup Procedure
The MAX17595 EV kit is fully assembled and tested.
Follow these steps to verify board operation. Caution:
Do not turn on the power supply until all connections
are completed.
1) Connect the positive lead of a DC voltmeter to the
VOUT PCB pad.
2) Connect the negative lead of a DC voltmeter to the
GNDO PCB pad.
3) Make sure that the isolation transformer is not pow-
ered up. Connect the variac to the output of the
isolation transformer.
4) Connect one lead of an AC voltmeter to the wiper
terminal of the variac.
5) Connect the other lead of the AC voltmeter to one of
the fixed terminals of the variac.
6) Set the output voltage of the variac to 0V AC.
7) Connect the wiper terminal of the isolated variac to
the AC1 PCB pad on the EV kit.
8) Connect the fixed tap of the isolated variac to the
AC2 PCB pad on the EV kit.
9) Power up the isolation transformer and gradually
increase the voltage of the variac to 85V AC and up
to 265V AC.
10) Verify that VOUT is 15V throughout the 85V AC to
265V AC input voltage range.
Detailed Description of Hardware
The MAX17595 EV kit evaluates MAX17595 off-line fly-
back converter operating in discontinuous-conduction
mode (DCM), configured for a 15V DC, 1.5A output.
This EV kit uses the peak current mode, pulse-width
modulating (PWM) controller IC in a 16-pin TQFN pack-
age with an exposed pad. A simple RC charging circuit
is used to start up the device. Bias winding feedback is
used to supply power during normal operation. Input DC
bus capacitor (C5) is designed based on 100Hz ripple
content. The 100Hz ripple is chosen to be 25% at 85V
AC and 1.5A load current. This PWM controller varies
the duty cycle to compensate for the variation in V
IN
and the output load to maintain a constant output volt-
age. The duty cycle determines the on /off duration of
the MOSFET (N1). The n-channel MOSFET is used as a
switch to control the current through the primary winding
of transformer T1.
The duty cycle is controlled by the feedback loop con-
sisting of voltage-divider resistors (R28, R29), a shunt
regulator (U3), an optocoupler (U2), and the PWM com-
parator inside the IC. This network provides isolated-volt-
age-mode feedback, regulating the output voltage to 15V
Q2% with up to 3500V
RMS
galvanic isolation. A thermistor
(R1) prevents high inrush currents present due to charg-
ing the input capacitor at startup. A snubber circuit (D3,
C10, and R18) is used to prevent excessive drain volt-
ages due to leakage inductance of the transformer.
Current Limit
The IC features current limiting for the transformer’s
primary side by monitoring the peak current through the
sense resistor (R21). Resistor R21 sets the EV kit circuit
peak current (I
PEAK
) to 1.52A. The IC turns off the N1
MOSFET when the peak current reaches the current limit.
To reconfigure the peak current limit to a different value,
use the following equation to choose a new R21 resistor:
= Ω
PEAK
305
R21 m
I
where I
PEAK
is in amps and R21 is in mI.
Undervoltage Lockout
and Overvoltage Protection
The EV kit features a UVLO and OVI circuit that pre-
vents operation below the programmed input supply
startup voltage and above the overvoltage threshold.
Resistors R2–R6 set the undervoltage and overvoltage
thresholds. The circuit undervoltage and overvoltage
thresholds are set at 60V AC (85V DC) and 274V AC
(387V DC), respectively. To reconfigure the UVLO and
OVI voltages, refer to the Startup Voltage and Input
Overvoltage Protection Setting (EN/UVLO, OVI) section
in the MAX17595/MAX17596 /MAX17597 IC data sheet.