Rainbow Electronics MAX17031 - Manual (Page 10)

MAX17031
Dual Quick-PWM Step-Down Controller with Low-
Power LDO and RTC Regulator for MAIN Supplies
10 ______________________________________________________________________________________
Pin Description
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V IN = 12V, V DD = V CC = 5V, T A = +25°C, unless otherwise noted.)
PIN NAME FUNCTION
1 REF
2V Reference Voltage Output. Bypass REF to analog ground with a 0.22µF 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 (see Typical Operating Characteristics).
The reference shuts down when ON1, ON2, and ONLDO are all pulled low.
2 ONLDO
Enable Input for LDO5. Drive ONLDO high (pull up to RTC) to enable the linear regulator (LDO5)
output. Drive ONLDO low to shut down the linear regulator output. When ONLDO is high, LDO5
must supply V
CC and V DD .
3 V CC
Analog Supply Voltage Input. Connect V CC to the system supply voltage with a series 50

resistor, and bypass to analog ground using a 1µF or greater ceramic capacitor.
4 RTC
3.3V Always-On Linear Regulator Output for RTC Power. Bypass RTC with a 1µF or greater ceramic
capacitor to analog ground. RTC can source up to 5mA for external loads.
5 IN
Power Input Supply. Bypass IN with a 0.1µF or greater ceramic capacitor to GND. IN powers the
linear regulators (RTC and LDO5) and senses the input voltage for the Quick-PWM on-time one-
shot timer. The DH on-time is inversely proportional to input voltage.
6 LDO5
5V Linear Regulator Output. Bypass LDO5 with a 4.7µF or greater ceramic capacitor to GND. LDO5
can source 100mA for external load support. LDO5 is powered from IN.
7 OUT1
Output-Voltage Sense Input for SMPS1 and Linear Regulator Bypass Input. OUT1 is an input to the
Quick-PWM on-time one-shot timer. OUT1 also serves as the feedback input for the SMPS1.
When OUT1 exceeds 93.5% of the LDO5 voltage, the controller bypasses the LDO5 output to
OUT1. The bypass switch is disabled if the OUT1 voltage drops by 8.5% from LDO5 nominal
regulation threshold.
8 ILIM1
Valley Current-Limit Adjustment for SMPS1. The GND - LX1 current-limit threshold is 1/10 the
voltage present on ILIM1 over a 0.2V to 2V range. An internal 5µA current source allows this
voltage to be set with a single resistor between ILIM1 and analog ground.
C. INDUCTOR CURRENT,
2A/div
5V SMPS LOAD TRANSIENT
(1A TO 4A)
MAX17031 toc19
A. LOAD CURRENT, 2A/div
B. 5V SMPS OUTPUT,
100mV/div
40 µs/div
4A
0A
0A
5V
A
B
C
C. INDUCTOR CURRENT,
2A/div
3.3V SMPS LOAD TRANSIENT
(1A TO 4A)
MAX17031 toc20
A. LOAD CURRENT, 2A/div
B. 3.3V SMPS OUTPUT,
100mV/div
40 µs/div
4A
0A
0A
3.3V
A
B
C
C. 5V SMPS, 2V/div
D. PGOOD, 5V/div
POWER REMOVAL
(SMPS UVLO RESPONSE)
MAX17031 toc21
A. INPUT VOLTAGE, 5V/div
B. 5V LDO OUTPUT, 2V/div
10ms/div
12V
5V
5V
5V
A
0V
B
0V
C
0V
D
0V