Typical operating characteristics (continued), Pin description – Rainbow Electronics MAX1845 User Manual
Page 8
MAX1845
Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
8
_______________________________________________________________________________________
MAX1845 toc09
400µs/div
V
OUT2
1V/div
I
OUT2
2A/div
STARTUP WAVEFORM
(4A COMPONENTS, SKIP = GND, V
OUT2
= 2.5V)
MAX1845 toc09
100
µs/div
V
OUT2
1V/div
I
OUT2
5A/div
SHUTDOWN WAVEFORM
(4A COMPONENTS, SKIP = GND, V
OUT2
= 2.5V)
Typical Operating Characteristics (continued)
(Circuit of Figure 1, components from Table 1, V
IN
= 15V, SKIP = GND, TON = unconnected, T
A
= +25°C, unless otherwise noted.)
PIN
NAME
FUNCTION
1
OUT1
Output Voltage Connection for the OUT1 PWM. Connect directly to the junction of the external
inductor and output filter capacitors. OUT1 senses the output voltage to determine the on-time and
also serves as the feedback input in fixed-output modes.
2
FB1
Feedback Input for OUT1. Connect to GND for 1.8V fixed output or to V
CC
for 1.5V fixed output, or
connect to a resistor-divider network from OUT1 for an adjustable output between 1V and 5.5V.
3
ILIM1
Current-Limit Threshold Adjustment for OUT1. The current-limit threshold at CS1 is 0.1 times the
voltage at ILIM1. Connect a resistor-divider network from REF to set the current-limit threshold
between 25mV and 250mV (with 0.25V to 2.5V at ILIM). Connect to V
CC
to assert 50mV default
current-limit threshold.
4
V+
Battery Voltage-Sense Connection. Connect to input power source. V+ is only used to adjust the
DH_ on-time for pseudo-fixed-frequency operation.
On-Time Selection Control Input. This four-level input pin sets the DH_ on-time to determine the
operating frequency.
TON
FREQUENCY (OUT1) (kHz)
FREQUENCY (OUT2) (kHz)
GND
620
460
REF
485
355
Open
345
255
5
TON
V
CC
235
170
Pin Description
MAX1845 toc07b
I
OUT1
5A/div
20
µs/div
V
OUT1
100mV/div
LOAD-TRANSIENT RESPONSE
(8A COMPONENTS, PWM MODE, V
OUT1
= 1.8V)