MAX1889ETE Maxim Integrated Products, MAX1889ETE Datasheet - Page 14

• Manufacturer Part Number: MAX1889ETE
• Description: DC/DC Switching Converters
• Manufacturer: Maxim Integrated Products

Specifications of MAX1889ETE

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Triple-Output TFT LCD Power Supply
with Fault Protection
Depending on the input-to-output voltage ratio, the reg-
ulator controls the output voltage and the power deliv-
ered to the output by modulating the duty cycle (D) of
the power MOSFET in each switching cycle. The duty
cycle of the MOSFET is approximated by:
On the rising edge of the internal clock, the controller
sets a flip-flop, which turns on the N-channel MOSFET
(Figure 3). The input voltage is applied across the
Figure 3. Main Step-Up Regulator Functional Diagram
14
______________________________________________________________________________________
OSC
D
FAULT M
≈
SSDONE
V
MAIN
V
MAX1889
MAIN
-
V
+
-
IN
+
-
Σ
COMPARATOR
RESET DOMINANT
ILIM
S
R
+
+
+
-
-
-
+
-
+
-
Q
ILIM
inductor. The inductor current ramps up linearly, storing
energy in a magnetic field. Once the sum of the feed-
back voltage error-amplifier output, slope-compensa-
tion, and current-feedback signals trip the multi-input
PWM comparator, the MOSFET turns off, and the flip-
flop resets. Since the inductor current is continuous, a
transverse potential develops across the inductor that
turns on the diode (D1). The voltage across the inductor
becomes the difference between the output voltage and
the input voltage. This discharge condition forces the
current through the inductor to ramp back down, trans-
ferring the energy to the output capacitor and the load.
The MOSFET remains off for the rest of the clock cycle.
REFOUT
SSOK
SOFT-START
CURRENT
SENSE
REFIN
CLK
EN
LX
PGND
SLOPE_COMP
FB
REF
ONMN