MAX5052/MAX5053
Detailed Description
The MAX5052/MAX5053 are current-mode PWM con-
trollers that have been specifically designed for use in
isolated and nonisolated power-supply applications. A
bootstrap UVLO with a large hysteresis (11.9V), very
low startup current, and low operating current result in
efficient universal-input power supplies. In addition to
the internal bootstrap UVLO, these devices also offer
programmable input startup voltage programmed
through the UVLO/EN pin. This feature is useful in pre-
venting the power supply from entering a brownout
condition, in case the input voltage drops below its
minimum value. This is important since switching power
supplies increases their input supply current as the
input voltage drops in order to keep the output power
constant. The MAX5052 is well suited for universal input
(rectified 85VAC to 265VAC) or telecom (-36VDC to
-72VDC) power supplies. The MAX5053 is well suited for
low-input-voltage (10.8VDC to 24VDC) power supplies.
Power supplies designed with the MAX5052 use a
high-value startup resistor, R1, that charges a reservoir
capacitor, C1 (see Figure 1). During this initial period,
while the voltage is less than the internal bootstrap
UVLO threshold, the device typically consumes only
45µA of quiescent current. This low startup current and
the large bootstrap UVLO hysteresis helps to minimize
Current-Mode PWM Controllers with an Error
Amplifier for Isolated/Nonisolated Power Supplies
6 _______________________________________________________________________________________
Pin Description
Externally Programmable Undervoltage Lockout. UVLO programs the input start voltage. Connect UVLO to
GND to disable the device.
2FBError-Amplifier Inverting Input
3 COMP Error-Amplifier Output
4CS
Current-Sense Connection for PWM Regulation and Overcurrent Protection. Connect to high side of sense
resistor. An RC filter may be necessary to eliminate leading-edge spikes.
5 GND Power-Supply Ground
6 NDRV External N-Channel MOSFET Gate Connection
7V
CC
Gate-Drive Supply. Internally regulated down from V
IN
. Decouple with a 10nF or larger capacitor to GND.
8V
IN
IC Supply. Decouple with a 10nF or larger capacitor to GND. For bootstrapped operation (MAX5052)
connect a startup resistor from the input supply line to V
IN
. Connect the bias winding supply to this point as
well (see the Typical Operating Circuit). For the MAX5053, connect V
IN
directly to 10.8V to 24V supply.
