MIC7400_15 Datasheet, PDF (26/68 Pages) Micrel Semiconductor – Configurable PMIC, Five-Channel Buck Regulator Plus One-Boost with HyperLight Load® and I2C Control

Micrel, Inc.
The soft-start time t_SS can be calculated by Equation 1:
MIC7400
t _SS
=


V_OUT − 0.15V
50mV
 ×

t_RAMP
Eq. 1
Where:
t_SS = Output rise time
V_OUT = Output voltage
t_RAMP = Output dwell time
For example:
t _SS
=


1.8V − 0.15V
50mV


×
8ms
t_SS = 264ms
Where:
V_OUT = 1.8V
t_RAMP = 8.0µs
Figure 2. Buck Soft-Start
Buck Digital Voltage Control (DVC)
The output voltage has a 6-bit control DAC that can be
programmed from 0.8V to 3.3V in 50mV increments. If
the output is programmed to a higher voltage, then the
output ramps up, as shown in Figure 3.
Table 1. Buck Outputs Default Soft-Start Time (DEFAULT)
VOUT
(V)
tRAMP
(µs)
tSS
(µs)
VOUT1
1.8
8
264
VOUT2
1.1
8
152
VOUT3
1.8
8
264
VOUT4
1.05
8
144
VOUT5
1.25
8
176
Figure 2 shows the output of Buck 1 ramping up cleanly,
starting from 0.15V to its final 1.1V value.
Figure 3. Buck DVC Control Ramp
March 3, 2015
26
Revision 2.0