MAX5071 Maxim Integrated Products, MAX5071 Datasheet - Page 13

• Manufacturer Part Number: MAX5071
• Description: (MAX5070 / MAX5071) Current-Mode PWM Controllers
• Manufacturer: Maxim Integrated Products

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Figure 3. MAX5071C Functional Diagram
In normal operation, V
ing of the transformer. However, at startup there is no
energy delivered through the transformer, thus a resistor
must be connected from V
(see R
charges up through R
comparator, error amplifier, oscillator, and drive circuit
remain off during UVLO to reduce startup current below
65µA. When V
threshold of 16V, the output driver begins to switch and
the tertiary winding will supply power to V
internal 26.5V current-limited clamp at its input to protect
the device from overvoltage during startup.
High-Performance, Single-Ended, Current-Mode
ST
ADV_CLK
MAX5071C
COMP
and C
GND
CS
3
5
1
2
ST
CC
______________________________________________________________________________________
in Figures 5 to 8). During startup, C
reaches the undervoltage-lockout
CC
ST
. The 5V reference generator,
is derived from a tertiary wind-
CC
to the input power source
V
2R
CC
1V
EN-DRV-BAR
CC
and Startup
ILIM
. V
R
CPWM
CC
1V
has an
DELAY
REFERENCE
2.5V
2.5V
ST
2.5V
REG_OK
Size the startup resistor, R
mum startup bias (I
and the charging current for C
C
t
capacitor depends on:
1) IC operating supply current at a programmed oscilla-
2) The time required for the bias voltage, derived from
3) The MOSFET total gate charge.
4) The operating frequency of the converter (f
ST
OSC Q
ST
PREREGULATOR
tor frequency (f
a bias winding, to go from 0 to 11V.
(for example, 500ms). The size of the startup
must charge to 16V within the desired time period
VP
5V
CLK
SHUTDOWN
THERMAL
S
R
PWM Controllers
Q
OSC
EN-REF
BG
SNS
VP
UVLO
START
5V REGULATOR
).
VOLTAGE-
DIVIDER
16V/10V
V
DD
ST
) of the device (65µA max)
, to supply both the maxi-
ST
50% MAX DUTY CYCLE
. The startup capacitor
VOLTAGE-
DIVIDER
26.5V
7
8
6 OUT
4 R
V
VREF
CC
T
SW
/C
T
).
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