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

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Pin Description

NDRV OUTPUT IMPEDANCE

vs. TEMPERATURE

TEMPERATURE (°C)

60

40

20

0

-20

3.2

3.4

3.6

3.8

4.0

4.2

4.4

4.6

4.8

5.0

3.0

-40

80

SOURCING 20mA

ERROR AMP OPEN-LOOP GAIN

AND PHASE vs. FREQUENCY

MAX5052 toc20

FREQUENCY (Hz)

10M

1M

10k

1k

100k

10

100

1

-80

-60

-20

-40

0-70

20

60

40

80

100

120

-100

-150

-130

-90

-110

-50

-10

-30

10

30

50

-170

0.1

100M

GAIN

PHASE

Typical Operating Characteristics (continued)

PIN

NAME

FUNCTION

1

UVLO/EN

Externally Programmable Undervoltage Lockout. UVLO programs the input start voltage. Connect UVLO to

GND to disable the device.

2FB

Error-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

IC Supply. Decouple with a 10nF or larger capacitor to GND. For bootstrapped operation (MAX5052)