Rainbow Electronics MAX1541 - Manual (Page 17)

MAX1540/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
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PIN
MAX1540 MAX1541
NAME FUNCTION
6 8 ILIM1
Valley Current-Limit Threshold Adjustment for Controller 1. The valley current-limit
threshold defaults to 50mV if ILIM1 is tied to V
CC . In adjustable mode, the valley
current-limit threshold across CSP1 and CSN1 is precisely 1/10 the voltage seen at
ILIM1 over a 250mV to 2.5V range. The logic threshold for switchover to the 50mV
default value is approximately V
CC - 1V. When the inductor-saturation protection
threshold is exceeded, ILIM1 sinks 6µA. See the Current-Limit Protection section.
7 9 ILIM2
Valley Current-Limit Threshold Adjustment for Controller 2. The valley current-limit
threshold defaults to 50mV if ILIM2 is tied to V
CC . In adjustable mode, the valley
current-limit threshold across CSP2 and CSN2 is precisely 1/10th the voltage seen at
ILIM2 over a 250mV to 2.5V range. The logic threshold for switchover to the 50mV
default value is approximately V
CC - 1V. When the inductor-saturation protection
threshold is exceeded, ILIM2 sinks 6µA. See the Current-Limit Protection section.
8 10 REF
2.0V Reference Voltage Output. Bypass REF to analog ground with a 0.1µF or greater
ceramic capacitor. The reference can source up to 50µA for external loads. Loading
REF degrades output voltage accuracy according to the REF load-regulation error.
The reference is disabled when the MAX1540/MAX1541 are shut down.
— 11 REFIN1
External Reference Input for Controller 1. REFIN1 sets the main feedback regulation
voltage (V
FB1 = V REFIN1 ) of the MAX1541.
— 12 OD Open-Drain Output. Controlled by GATE.
9 13 CSP2
Positive Current-Sense Input for Controller 2. 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 ILIM2.
10 14 CSN2
Negative Current-Sense Input for Controller 2. 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 ILIM2.
11 15 FB2
Feedback Input for Controller 2:
M AX 1540: C onnect to V
C C for a + 1.5V fi xed outp ut or to anal og g r ound ( G N D ) for a
+ 2.5V fi xed outp ut. For an ad j ustab l e outp ut ( 0.7V to 5.5V ) , connect FB2 to a r esi sti ve
d i vi d er fr om OU T2. The FB2 r eg ul ati on l evel i s + 0.7V .
M AX 1541: C onnect to V C C for a + 1.8V fi xed outp ut or to anal og g r ound ( G N D ) for a
+ 2.5V fi xed outp ut. For an ad j ustab l e outp ut ( 0.7V to 5.5V ) , connect FB2 to a r esi sti ve
d i vi d er fr om OU T2. The FB2 r eg ul ati on l evel i s + 0.7V .
12 16 OUT2
Output Voltage-Sense Connection for Controller 2. Connect directly to the positive
terminal of the output capacitors as shown in the standard application circuits
(Figures 1 and 12). OUT2 senses the output voltage to determine the on-time for the
high-side switching MOSFET. OUT2 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 OUT2 and ground.
Pin Description (continued)