Rainbow Electronics MAX1541 - Manual (Page 19)

MAX1540/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
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PIN
MAX1540 MAX1541
NAME FUNCTION
24 31 LX1
Inductor Connection for Controller 1. Connect to the switched side of the inductor.
LX1 serves as the lower supply rail for the DH1 high-side gate driver.
25 32 DH1 High-Side Gate-Driver Output for Controller 1. DH1 swings from LX1 to BST1.
26 33 PGOOD1
Open-Drain Power-Good Output. PGOOD1 is low when the output voltage is more
than 10% (typ) above or below the normal regulation point, during soft-start, and in
shutdown. After the soft-start circuit has terminated, PGOOD1 becomes high
impedance if the output is in regulation. For the MAX1541, PGOOD1 is
blanked—forced high-impedance state—when FBLANK is enabled and the controller
detects a transition on GATE.
27 34 OUT1
Output Voltage-Sense Connection for Controller 1. Connect directly to the positive
terminal of the output capacitors as shown in the standard application circuits
(Figures 1 and 12). OUT1 senses the output voltage to determine the on-time for the
high-side switching MOSFET. For the MAX1540, OUT1 also serves as the feedback
input when using the preset internal output voltages as shown in Figure 10. When
discharge mode is enabled by OVP/UVP, the output capacitor is discharged through
an internal 10
Ω resistor connected between OUT1 and ground.
28 35 FB1
Feedback Input for Controller 1:
M AX 1540: C onnect to V
C C for a + 1.2V fi xed outp ut or to anal og g r ound ( G N D ) for a
+ 1.8V fi xed outp ut. For an ad j ustab l e outp ut ( 0.7V to 5.5V ) , connect FB1 to a r esi sti ve
d i vi d er fr om OU T1. The FB1 r eg ul ati on l evel i s + 0.7V .
M AX 1541: The FB1 r eg ul ati on l evel i s set b y the vol tag e at RE FIN 1.
29 36 CSN1
Negative Current-Sense Input for Controller 1. Connect to the negative terminal of the
current-sense element. Figure 14 and Table 9 describe several current-sensing
options. The PWM controller does not begin a cycle unless the current sensed is less
than the valley current-limit threshold programmed at ILIM1.
30 37 CSP1
Positive Current-Sense Input for Controller 1. Connect to the positive terminal of the
current-sense element. Figure 14 and Table 9 describe several current-sensing
options. The PWM controller does not begin a cycle unless the current sensed is less
than the valley current-limit threshold programmed at ILIM1.
— 38 FBLANK
Fault-Blanking Control Input. This four-level logic input enables or disables fault
blanking, and sets the forced-PWM operation time (t
FBLANK
). When fault blanking is
enabled, PGOOD1 and the OVP/UVP protection for controller 1 are blanked for the
selected time period after the MAX1541 detects a transition on GATE. Additionally,
controller 1 enters forced-PWM mode for the duration of t
FBLANK anytime GATE
changes states. Connect FBLANK as follows:
V
CC = 220µs t FBLANK , fault blanking enabled.
Open = 140µs t FBLANK , fault blanking enabled.
REF = 65µs t FBLANK , fault blanking enabled.
GND = 140µs t FBLANK , fault blanking disabled.
See the Electrical Characteristics table for the t FBLANK limits.
Pin Description (continued)