HA16114P Datasheet, PDF (17/38 Pages) Hitachi Semiconductor – Switching Regulator for Chopper Type DC/DC Converter

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7.2 Intermittent Mode Timing Diagram (V_ON/OFF only)
3V_BE*1
V _ON/OFF
2V_BE
c
c
On
On
V_BE
IC is on
IC is off
Off
a
b
0V
T_ON
t
2T_ON
T_OFF
a. Continuous overcurrent is detected
b. Intermittent operation starts (IC is off)
c. Voltage if overcurrent ends (thick dotted line)
Note: 1. V_BE is the base-emitter voltage of internal transistors, and is approximately 0.7 V.
(See the figure 6.1.)
For details, see the overall waveform timing diagram.
Figure 7.2 Intermittent Mode Timing Diagram (V_ON/OFF only)
7.3 Calculation of Intermittent Mode Timing
Intermittent mode timing is calculated as follows.
(1) T_ON (time until the IC shuts off when continuous overcurrent occurs)
T_ON = C_ON/OFF × R_B × ln
2V_BE
V_BE
×
1
1 − On duty*
= C_ON/OFF × R_B × ln2 ×
1
1 − On duty*
≈ 0.69 × C_ON/OFF × R_B ×
1
1 − On duty*
(2) T_OFF (time from when the IC shuts off until it next turns on)
T_OFF = C_ON/OFF × (R_A + R_B) × ln
V_IN − V_BE
V_IN − 2V_BE
Where V_BE ≈ 0.7 V
The greater the overload, the sooner the pulse-by-pulse current limiter operates, the smaller t_ON becomes,
and from the first equation (1) above, the smaller T_ON becomes. From the second equation (2), T_OFF
depends on V_IN. Note that with the connections shown in the diagram, when V_IN is switched on the IC does
not turn on until T_OFF has elapsed.
Sawtooth wave
Dead-band voltage
PWM output
(In case of HA16114)
Point at which the current
limiter operates
t_ON
On duty = ^{t ON} × 100 (%)
T
T
Where T = t/f _OSC
Note: On duty is the percent of time the IC output is on during one PWM cycle
when the pulse-by-pulse current limiter is operating.
Figure 7.3
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