MAX17024 Datasheet, PDF (14/25 Pages) Maxim Integrated Products – Single Quick-PWM Step-Down Controller with Dynamic REFIN

Single Quick-PWM Step-Down
Controller with Dynamic REFIN
5V BIAS
SUPPLY
AGND
ON OFF
AGND
C1
4.7µF
1 _VDD
PWR
TON ⁷
BST ⁶
C2
1µF
MAX17024
13 _VCC
DH ⁵
R_TON
332kΩ
C_BST
0.1µF
R4
100kΩ
14 _PGOOD
4
LX
2
DL
12 _EN
C3
1nF
11 _REF
10 _REFIN
9
CS
8
PWR
FB
GND (EP)
AGND PWR
INPUT
7V TO 24V
C_IN
PWR
L1
R6
13.0kΩ
C_OUT
PWR
OUTPUT
3.3V
R_CS
R7
20.0kΩ
AGND
Figure 3. High Output-Voltage Application Using a Feedback Divider
Output Voltages Greater than 2V
Although REFIN is limited to a 0 to 2V range, the out-
put-voltage range is unlimited since the MAX17024 uti-
lizes a high-impedance feedback input (FB). By adding
a resistive voltage-divider from the output to FB to ana-
log ground (Figure 3), the MAX17024 supports output
voltages above 2V. However, the controller also uses
FB to determine the on-time, so the voltage-divider
influences the actual switching frequency, as detailed
in the On-Time One-Shot section.
Internal Integration
An integrator amplifier forces the DC average of the FB
voltage to equal the target voltage. This internal amplifi-
er integrates the feedback voltage and provides a fine
adjustment to the regulation voltage (Figure 2), allowing
accurate DC output-voltage regulation regardless of the
compensated feedback ripple voltage and internal
slope-compensation variation. The integrator amplifier
has the ability to shift the output voltage by ±55mV (typ).
The MAX17024 disables the integrator by connecting the
amplifier inputs together at the beginning of all downward
REFIN transitions done in pulse-skipping mode. The inte-
grator remains disabled until 20µs after the transition is
completed (the internal target settles) and the output is in
regulation (edge detected on the error comparator).
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