MAX5974CETE+ Maxim Integrated Products, MAX5974CETE+ Datasheet - Page 16

• Manufacturer Part Number: MAX5974CETE+
• Description: Current Mode PWM Controllers ACTIVE-CLAMPED CUR MODE PWM CONTLR
• Manufacturer: Maxim Integrated Products

Specifications of MAX5974CETE+

• Duty Cycle (max): 82 %
• Mounting Style: SMD/SMT
• Switching Frequency: 600 KHz
• Operating Supply Voltage: 12 V to 21 V
• Supply Current: 1.8 mA
• Maximum Operating Temperature: + 85 C
• Fall Time: 14 ns
• Minimum Operating Temperature: - 40 C
• Rise Time: 27 ns
• Package / Case: TQFN-16
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 1. Programmable UVLO for the Power Source
Figure 2. External Control of the Enable Input
Active-Clamped, Spread-Spectrum,
Current-Mode PWM Controllers
16
CONTROL
DIGITAL
CONTROL
DIGITAL
N
C
V
R
IN
S
IN
V
S
R
R
EN1
EN2
N
R
IN
IN
EN
C
IN
MAX5974
IN
EN
MAX5974
The devices have an internal bootstrap UVLO that is very
useful when designing high-voltage power supplies (see
the Block Diagrams). This allows the device to bootstrap
itself during initial power-up. The MAX5974A/MAX5974C
soft-start when V
old of V
Because the MAX5974B/MAX5974D are designed for
use with low-voltage power sources such as wall adapt-
ers outputting 12V to 24V, they have a lower UVLO
wake-up threshold of 10V.
The device starts up when the voltage at IN exceeds
20V (MAX5974A/MAX5974C) or 10V (MAX5974B/
MAX5974D) and the enable input voltage is greater than
1.26V.
During normal operation, the voltage at IN is nor-
mally derived from a tertiary winding of the transformer
(MAX5974C/MAX5974D). However, at startup there is
no energy being delivered through the transformer;
hence, a special bootstrap sequence is required. In the
Typical Application Circuits, C
startup resistor, R
100FA of the current supplied through R
the ICs, the remaining input current charges C
V
V
n-channel MOSFET and transfers energy to the second-
ary and tertiary outputs. If the voltage on the tertiary
output builds to higher than 7V (the bootstrap UVLO
shutdown level), then startup has been accomplished
and sustained operation commences. If V
7V before startup is complete, the device goes back to
low-current UVLO. In this case, increase the value of C
in order to store enough energy to allow for the voltage
at the tertiary winding to build up.
While the MAX5974A/MAX5974B derive their input volt-
age from the coupled inductor output during normal
operation, the startup behavior is similar to that of the
MAX5974C/MAX5974D.
A capacitor from SS to GND, C
start time. V
IN
IN
reaches the bootstrap UVLO wake-up level. Once
exceeds this level, NDRV begins switching the
INUVR
SS
Bootstrap Undervoltage Lockout
(20V typ).
controls the oscillator duty cycle during
IN
IN
exceeds the bootstrap UVLO thresh-
, to an intermediate voltage. Only
IN
SS
Startup Operation
charges through the
, programs the soft-
IN
IN
Soft-Start
drops below
is used by
IN
until
IN