Datasheet

MAX17499/MAX17500
Detailed Description
The MAX17499/MAX17500 current-mode PWM con-
trollers are ideal for isolated and nonisolated power-
supply applications. The devices offer an accurate
input startup voltage programmable through the
UVLO/EN input. This feature prevents the power supply
from entering a brownout condition in case the input
voltage sags below its minimum value. This is important
since switching power supplies increases their input
supply current as the input voltage drops to keep the
output power constant. In addition to this externally
adjustable UVLO feature, the MAX17500 also offers a
bootstrap UVLO with a large hysteresis (11.9V) and
very low startup and operating current, which result in
an efficient universal input power supply. The switching
frequency of the devices is programmable with an
external resistor.
The MAX17500 is well suited for universal input (recti-
fied 85V AC to 265V AC) or telecom (-36V DC to
-72V DC) power supplies. The MAX17499 is well suited
for low-input-voltage (9.5V DC to 24V DC) power sup-
plies. The devices include an internal clamp at IN to
prevent the input voltage from exceeding the absolute
maximum rating (see Note 2 at the end of the
Electrical
Characteristics table). The input is clamped when the
devices are started with a bleed resistor (R1 in Figure 1)
from a high input voltage and the UVLO/EN input is low.
The clamp can safely sink up to 2mA current.
Current-Mode PWM Controllers with
Programmable Switching Frequency
8 _______________________________________________________________________________________
8
9
10
3
2
1
UVLO/EN
IN
7
4
V
CC
NDRV
GND
UFLG
FB
COMP
6
5
RT
CS
T1
R3
R2
R12
R1
R4
C5
C2
C2
C1
C4
D2
D1
C6
R11
V
SUPPLY
0V
R13
R14
V
OUT
R15
Q1
MAX17500
Figure 1. Nonisolated Power Supply with Programmable Input-Supply Start Voltage
Pin Description (continued)
PIN
NAME
FUNCTION
7 GND Ground Connection
8
NDRV
External n-Channel MOSFET Gate Connection
9V
CC
Gate-Drive Supply. Internally generated supply from IN. Decouple V
CC
with a 10nF or larger capacitor
to GND.
10 IN
IN Supply. Decouple with a 10nF or larger capacitor to GND. For bootstrapped operation (MAX17500),
connect a startup resistor from the input supply line to IN. Connect the bias winding supply to IN also (see
the Typical Application Circuit). For the MAX17499, connect IN directly to the 9.5V to 24V supply.