MAX1540A Datasheet, PDF (17/49 Pages) Maxim Integrated Products – Dual Step-Down Controllers with Saturation Protection, Dynamic Output, and Linear Regulator

Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
PIN
MAX1540A MAX1541
6
8
7
9
8
10
—
11
—
12
9
13
10
14
11
15
12
16
Pin Description (continued)
NAME
ILIM1
ILIM2
REF
REFIN1
OD
CSP2
CSN2
FB2
OUT2
FUNCTION
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.
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.
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 MAX1540A/MAX1541 are shut down.
External Reference Input for Controller 1. REFIN1 sets the main feedback regulation
voltage (V_FB1 = V_REFIN1) of the MAX1541.
Open-Drain Output. Controlled by GATE.
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.
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.
Feedback Input for Controller 2:
MAX1540A: Connect to V_CC for a +1.5V fixed output or to analog ground (GND) for a
+2.5V fixed output. For an adjustable output (0.7V to 5.5V), connect FB2 to a resistive
divider from OUT2. The FB2 regulation level is +0.7V.
MAX1541: Connect to V_CC for a +1.8V fixed output or to analog ground (GND) for a
+2.5V fixed output. For an adjustable output (0.7V to 5.5V), connect FB2 to a resistive
divider from OUT2. The FB2 regulation level is +0.7V.
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 10Ω
resistor connected between OUT2 and ground.
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